Showing papers on "Perovskite (structure) published in 2018"
TL;DR: In this article, the authors describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20.3 per cent, which is achieved by a new strategy for managing the compositional distribution in the device.
Abstract: Metal halide perovskite materials are an emerging class of solution-processable semiconductors with considerable potential for use in optoelectronic devices1–3. For example, light-emitting diodes (LEDs) based on these materials could see application in flat-panel displays and solid-state lighting, owing to their potential to be made at low cost via facile solution processing, and could provide tunable colours and narrow emission line widths at high photoluminescence quantum yields4–8. However, the highest reported external quantum efficiencies of green- and red-light-emitting perovskite LEDs are around 14 per cent7,9 and 12 per cent8, respectively—still well behind the performance of organic LEDs10–12 and inorganic quantum dot LEDs13. Here we describe visible-light-emitting perovskite LEDs that surpass the quantum efficiency milestone of 20 per cent. This achievement stems from a new strategy for managing the compositional distribution in the device—an approach that simultaneously provides high luminescence and balanced charge injection. Specifically, we mixed a presynthesized CsPbBr3 perovskite with a MABr additive (where MA is CH3NH3), the differing solubilities of which yield sequential crystallization into a CsPbBr3/MABr quasi-core/shell structure. The MABr shell passivates the nonradiative defects that would otherwise be present in CsPbBr3 crystals, boosting the photoluminescence quantum efficiency, while the MABr capping layer enables balanced charge injection. The resulting 20.3 per cent external quantum efficiency represents a substantial step towards the practical application of perovskite LEDs in lighting and display. A strategy for managing the compositional distribution in metal halide perovskite light-emitting diodes enables them to surpass 20% external quantum efficiency—a step towards their practical application in lighting and displays.
2,346 citations
TL;DR: Jeon et al. as discussed by the authors synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable perovskite solar cells.
Abstract: Perovskite solar cells (PSCs) require both high efficiency and good long-term stability if they are to be commercialized. It is crucial to finely optimize the energy level matching between the perovskites and hole-transporting materials to achieve better performance. Here, we synthesize a fluorene-terminated hole-transporting material with a fine-tuned energy level and a high glass transition temperature to ensure highly efficient and thermally stable PSCs. We use this material to fabricate photovoltaic devices with 23.2% efficiency (under reverse scanning) with a steady-state efficiency of 22.85% for small-area (~0.094 cm2) cells and 21.7% efficiency (under reverse scanning) for large-area (~1 cm2) cells. We also achieve certified efficiencies of 22.6% (small-area cells, ~0.094 cm2) and 20.9% (large-area, ~1 cm2). The resultant device shows better thermal stability than the device with spiro-OMeTAD, maintaining almost 95% of its initial performance for more than 500 h after thermal annealing at 60 °C. Interfacial losses between device layers play a key role in determining characteristics of solar cells. Jeon et al. address this in perovskite solar cells by synthesizing a hole-transporting layer that is better matched to the surrounding layers, and show high-efficiency and high-stability devices.
1,771 citations
TL;DR: The formation of submicrometre-scale structure in perovskite light-emitting diodes can raise their external quantum efficiency beyond 20%, suggesting the possibility of both high efficiency and high brightness.
Abstract: Light-emitting diodes (LEDs), which convert electricity to light, are widely used in modern society—for example, in lighting, flat-panel displays, medical devices and many other situations. Generally, the efficiency of LEDs is limited by nonradiative recombination (whereby charge carriers recombine without releasing photons) and light trapping1–3. In planar LEDs, such as organic LEDs, around 70 to 80 per cent of the light generated from the emitters is trapped in the device4,5, leaving considerable opportunity for improvements in efficiency. Many methods, including the use of diffraction gratings, low-index grids and buckling patterns, have been used to extract the light trapped in LEDs6–9. However, these methods usually involve complicated fabrication processes and can distort the light-output spectrum and directionality6,7. Here we demonstrate efficient and high-brightness electroluminescence from solution-processed perovskites that spontaneously form submicrometre-scale structures, which can efficiently extract light from the device and retain wavelength- and viewing-angle-independent electroluminescence. These perovskites are formed simply by introducing amino-acid additives into the perovskite precursor solutions. Moreover, the additives can effectively passivate perovskite surface defects and reduce nonradiative recombination. Perovskite LEDs with a peak external quantum efficiency of 20.7 per cent (at a current density of 18 milliamperes per square centimetre) and an energy-conversion efficiency of 12 per cent (at a high current density of 100 milliamperes per square centimetre) can be achieved—values that approach those of the best-performing organic LEDs. The formation of submicrometre-scale structure in perovskite light-emitting diodes can raise their external quantum efficiency beyond 20%, suggesting the possibility of both high efficiency and high brightness.
1,404 citations
TL;DR: This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts, which led to a stabilized power output approaching 21% at the maximum power point.
Abstract: The highest power conversion efficiencies (PCEs) reported for perovskite solar cells (PSCs) with inverted planar structures are still inferior to those of PSCs with regular structures, mainly because of lower open-circuit voltages (Voc). Here we report a strategy to reduce nonradiative recombination for the inverted devices, based on a simple solution-processed secondary growth technique. This approach produces a wider bandgap top layer and a more n-type perovskite film, which mitigates nonradiative recombination, leading to an increase in Voc by up to 100 millivolts. We achieved a high Voc of 1.21 volts without sacrificing photocurrent, corresponding to a voltage deficit of 0.41 volts at a bandgap of 1.62 electron volts. This improvement led to a stabilized power output approaching 21% at the maximum power point.
1,117 citations
National University of Singapore1, China University of Geosciences (Beijing)2, Fuzhou University3, Hong Kong Polytechnic University4, King Abdullah University of Science and Technology5, Nanjing Tech University6, Shenzhen University7, Johns Hopkins University8, University of New South Wales9, University of Verona10, Northwestern Polytechnical University11, Nanjing University of Posts and Telecommunications12
TL;DR: All-inorganic perovskite nanocrystals containing caesium and lead provide low-cost, flexible and solution-processable scintillators that are highly sensitive to X-ray irradiation and emit radioluminescence that is colour-tunable across the visible spectrum.
Abstract: The rising demand for radiation detection materials in many applications has led to extensive research on scintillators1–3. The ability of a scintillator to absorb high-energy (kiloelectronvolt-scale) X-ray photons and convert the absorbed energy into low-energy visible photons is critical for applications in radiation exposure monitoring, security inspection, X-ray astronomy and medical radiography4,5. However, conventional scintillators are generally synthesized by crystallization at a high temperature and their radioluminescence is difficult to tune across the visible spectrum. Here we describe experimental investigations of a series of all-inorganic perovskite nanocrystals comprising caesium and lead atoms and their response to X-ray irradiation. These nanocrystal scintillators exhibit strong X-ray absorption and intense radioluminescence at visible wavelengths. Unlike bulk inorganic scintillators, these perovskite nanomaterials are solution-processable at a relatively low temperature and can generate X-ray-induced emissions that are easily tunable across the visible spectrum by tailoring the anionic component of colloidal precursors during their synthesis. These features allow the fabrication of flexible and highly sensitive X-ray detectors with a detection limit of 13 nanograys per second, which is about 400 times lower than typical medical imaging doses. We show that these colour-tunable perovskite nanocrystal scintillators can provide a convenient visualization tool for X-ray radiography, as the associated image can be directly recorded by standard digital cameras. We also demonstrate their direct integration with commercial flat-panel imagers and their utility in examining electronic circuit boards under low-dose X-ray illumination. All-inorganic perovskite nanocrystals containing caesium and lead provide low-cost, flexible and solution-processable scintillators that are highly sensitive to X-ray irradiation and emit radioluminescence that is colour-tunable across the visible spectrum.
1,064 citations
TL;DR: In this paper, a red perovskite quantum dot-based light-emitting devices were fabricated by anion exchange from pristine CsPbBr3 using halide-anion-containing alkyl ammonium and aryl ionium salts.
Abstract: Perovskite quantum dots have significant potential for light-emitting devices because of their high colour purity and colour tunability in the visible spectrum. Here, we report highly efficient red perovskite quantum dot-based light-emitting devices. The quantum dots were fabricated by anion exchange from pristine CsPbBr3 using halide-anion-containing alkyl ammonium and aryl ammonium salts. Anion-exchange quantum dots based on ammonium iodine salts exhibited a strong redshift from green emission to a deep-red emission at 649 nm as well as higher photoluminescence quantum yields. Furthermore, the quantum dot-based light-emitting device with the alkyl ammonium iodine salt exhibited an external quantum efficiency of 21.3% and high colour purity, with Commission Internationale de l’Eclairage coordinates of (0.72, 0.28), while the light-emitting device with the aryl ammonium iodine salt showed an external quantum efficiency of 14.1%. Finally, the operational stability of the latter was 36 times higher because the surface ligand density of the corresponding quantum dots was lower. Perovskite quantum dots (QDs) are synthesized via an anion-exchange process where CsPbBr3 is used to realize a highly efficient red light-emitting diode (LED). The perovskite QD-based LED exhibits the highest external quantum efficiency of more than 20% compared with perovskite LEDs.
999 citations
TL;DR: An optimized two-step deposition process allows the formation of uniform layers of metal halide perovskites on textured silicon layers, enabling tandem silicon/perovskite solar cells with improved optical design and efficiency.
Abstract: Tandem devices combining perovskite and silicon solar cells are promising candidates to achieve power conversion efficiencies above 30% at reasonable costs. State-of-the-art monolithic two-terminal perovskite/silicon tandem devices have so far featured silicon bottom cells that are polished on their front side to be compatible with the perovskite fabrication process. This concession leads to higher potential production costs, higher reflection losses and non-ideal light trapping. To tackle this issue, we developed a top cell deposition process that achieves the conformal growth of multiple compounds with controlled optoelectronic properties directly on the micrometre-sized pyramids of textured monocrystalline silicon. Tandem devices featuring a silicon heterojunction cell and a nanocrystalline silicon recombination junction demonstrate a certified steady-state efficiency of 25.2%. Our optical design yields a current density of 19.5 mA cm−2 thanks to the silicon pyramidal texture and suggests a path for the realization of 30% monolithic perovskite/silicon tandem devices.
990 citations
TL;DR: Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability and success in suppressing hysteresis and record efficiency for planars-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer.
Abstract: Even though the mesoporous-type perovskite solar cell (PSC) is known for high efficiency, its planar-type counterpart exhibits lower efficiency and hysteretic response. Herein, we report success in suppressing hysteresis and record efficiency for planar-type devices using EDTA-complexed tin oxide (SnO2) electron-transport layer. The Fermi level of EDTA-complexed SnO2 is better matched with the conduction band of perovskite, leading to high open-circuit voltage. Its electron mobility is about three times larger than that of the SnO2. The record power conversion efficiency of planar-type PSCs with EDTA-complexed SnO2 increases to 21.60% (certified at 21.52% by Newport) with negligible hysteresis. Meanwhile, the low-temperature processed EDTA-complexed SnO2 enables 18.28% efficiency for a flexible device. Moreover, the unsealed PSCs with EDTA-complexed SnO2 degrade only by 8% exposed in an ambient atmosphere after 2880 h, and only by 14% after 120 h under irradiation at 100 mW cm−2. The development of high efficiency planar-type perovskite solar cell has been lagging behind the mesoporous-type counterpart. Here Yang et al. modify the oxide based electron transporting layer with organic acid and obtain planar-type cells with high certified efficiency of 21.5% and decent stability.
972 citations
TL;DR: Solution-processable halide perovskites have high luminous efficiency and excellent chemical tunability, making them ideal candidates for light-emitting diodes, and Yang et al. achieve high external quantum efficiency of 14% in the devices by fine-tuning the phase and passivating the surface defects.
Abstract: Perovskite light-emitting diodes (LEDs) are attracting great attention due to their efficient and narrow emission. Quasi-two-dimensional perovskites with Ruddlesden–Popper-type layered structures can enlarge exciton binding energy and confine charge carriers and are considered good candidate materials for efficient LEDs. However, these materials usually contain a mixture of phases and the phase impurity could cause low emission efficiency. In addition, converting three-dimensional into quasi-two-dimensional perovskite introduces more defects on the surface or at the grain boundaries due to the reduction of crystal sizes. Both factors limit the emission efficiency of LEDs. Here, firstly, through composition and phase engineering, optimal quasi-two-dimensional perovskites are selected. Secondly, surface passivation is carried out by coating organic small molecule trioctylphosphine oxide on the perovskite thin film surface. Accordingly, green LEDs based on quasi-two-dimensional perovskite reach a current efficiency of 62.4 cd A−1 and external quantum efficiency of 14.36%.
719 citations
TL;DR: The perovskite absorber material itself has been heavily scrutinized for being prone to degradation by water, oxygen and ultraviolet light as discussed by the authors, and it has been shown that even under the combined stresses of light (including ultraviolet light), oxygen and moisture, perovsite solar cells can retain 94% of peak efficiency despite 1,000 hours of continuous unencapsulated operation in ambient air conditions (relative humidity of 10-20%).
Abstract: Long-term device stability is the most pressing issue that impedes perovskite solar cell commercialization, given the achieved 22.7% efficiency. The perovskite absorber material itself has been heavily scrutinized for being prone to degradation by water, oxygen and ultraviolet light. To date, most reports characterize device stability in the absence of these extrinsic factors. Here we show that, even under the combined stresses of light (including ultraviolet light), oxygen and moisture, perovskite solar cells can retain 94% of peak efficiency despite 1,000 hours of continuous unencapsulated operation in ambient air conditions (relative humidity of 10–20%). Each interface and contact layer throughout the device stack plays an important role in the overall stability which, when appropriately modified, yields devices in which both the initial rapid decay (often termed burn-in) and the gradual slower decay are suppressed. This extensively modified device architecture and the understanding developed will lead towards durable long-term device performance.
684 citations
TL;DR: In this article, a planar pin-type perovskite solar cells with undoped organic charge transport layers with photoluminescence imaging was used to visualize all non-radiative recombination pathways.
Abstract: The performance of perovskite solar cells is predominantly limited by non-radiative recombination, either through trap-assisted recombination in the absorber layer or via minority carrier recombination at the perovskite/transport layer interfaces. Here, we use transient and absolute photoluminescence imaging to visualize all non-radiative recombination pathways in planar pin-type perovskite solar cells with undoped organic charge transport layers. We find significant quasi-Fermi-level splitting losses (135 meV) in the perovskite bulk, whereas interfacial recombination results in an additional free energy loss of 80 meV at each individual interface, which limits the open-circuit voltage (VOC) of the complete cell to ~1.12 V. Inserting ultrathin interlayers between the perovskite and transport layers leads to a substantial reduction of these interfacial losses at both the p and n contacts. Using this knowledge and approach, we demonstrate reproducible dopant-free 1 cm2 perovskite solar cells surpassing 20% efficiency (19.83% certified) with stabilized power output, a high VOC (1.17 V) and record fill factor (>81%). Non-radiative recombination is a critical limiting factor for perovskite solar cell performance. Stolterfoht et al. visualize the various recombination pathways in planar pin cells with photoluminescence imaging and use it to design improved solar cells with 1 cm2 areas and ~20% efficiency.
TL;DR: Inorganic cation tuning, using rubidium and cesium, enables highly crystalline formamidinium-based perovskites without Br or MA, and this work demonstrates an efficiency of 20.35% (stabilized), one of the highest for MA-free perovSKites, with a drastically improved stability reached without the stabilizing influence of mesoporous interlayers.
Abstract: Currently, perovskite solar cells (PSCs) with high performances greater than 20% contain bromine (Br), causing a suboptimal bandgap, and the thermally unstable methylammonium (MA) molecule. Avoiding Br and especially MA can therefore result in more optimal bandgaps and stable perovskites. We show that inorganic cation tuning, using rubidium and cesium, enables highly crystalline formamidinium-based perovskites without Br or MA. On a conventional, planar device architecture, using polymeric interlayers at the electron- and hole-transporting interface, we demonstrate an efficiency of 20.35% (stabilized), one of the highest for MA-free perovskites, with a drastically improved stability reached without the stabilizing influence of mesoporous interlayers. The perovskite is not heated beyond 100°C. Going MA-free is a new direction for perovskites that are inherently stable and compatible with tandems or flexible substrates, which are the main routes commercializing PSCs.
TL;DR: A universal approach for hysteresis-free perovskite solar cells via defect engineering via KI doping and a series of experiments with alkali metal iodides of LiI, NaI, KI, RbI and CsI reveals that potassium ion is the right element for Hysteres is-freeperovskites.
Abstract: Organic–inorganic halide perovskite is believed to be a potential candidate for high efficiency solar cells because power conversion efficiency (PCE) was certified to be more than 22%. Nevertheless, mismatch of PCE due to current density (J)–voltage (V) hysteresis in perovskite solar cells is an obstacle to overcome. There has been much lively debate on the origin of J–V hysteresis; however, effective methodology to solve the hysteric problem has not been developed. Here we report a universal approach for hysteresis-free perovskite solar cells via defect engineering. A severe hysteresis observed from the normal mesoscopic structure employing TiO2 and spiro-MeOTAD is almost removed or does not exist upon doping the pure perovskites, CH3NH3PbI3 and HC(NH2)2PbI3, and the mixed cation/anion perovskites, FA0.85MA0.15PbI2.55Br0.45 and FA0.85MA0.1Cs0.05PbI2.7Br0.3, with potassium iodide. Substantial reductions in low-frequency capacitance and bulk trap density are measured from the KI-doped perovskite, which is ...
TL;DR: McGehee et al. as discussed by the authors discussed the recent developments in perovskite-based tandem fabrication, and detail directions for future research to take this technology beyond the proof-of-concept stage.
Abstract: Metal halide perovskite semiconductors possess excellent optoelectronic properties, allowing them to reach high solar cell performances. They have tunable bandgaps and can be rapidly and cheaply deposited from low-cost precursors, making them ideal candidate materials for tandem solar cells, either by using perovskites as the wide-bandgap top cell paired with low-bandgap silicon or copper indium diselenide bottom cells or by using both wide- and small-bandgap perovskite semiconductors to make all-perovskite tandem solar cells. This Review highlights the unique potential of perovskite tandem solar cells to reach solar-to-electricity conversion efficiencies far above those of single-junction solar cells at low costs. We discuss the recent developments in perovskite-based tandem fabrication, and detail directions for future research to take this technology beyond the proof-of-concept stage. Perovskites, with their wide bandgap range, are good partners for both commercial and novel photovoltaic technologies in multijunction solar cells. Here, McGehee and co-workers review recent material and device developments and highlight future challenges and opportunities for perovskite-based tandems.
TL;DR: A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb-I antisite defects and vacancies created by under-coordinated Pb atoms, and how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport.
Abstract: The trap states at grain boundaries (GBs) within polycrystalline perovskite films deteriorate their optoelectronic properties, making GB engineering particularly important for stable high-performance optoelectronic devices. It is demonstrated that trap states within bulk films can be effectively passivated by semiconducting molecules with Lewis acid or base functional groups. The perovskite crystallization kinetics are studied using in situ synchrotron-based grazing-incidence X-ray scattering to explore the film formation mechanism. A model of the passivation mechanism is proposed to understand how the molecules simultaneously passivate the Pb-I antisite defects and vacancies created by under-coordinated Pb atoms. In addition, it also explains how the energy offset between the semiconducting molecules and the perovskite influences trap states and intergrain carrier transport. The superior optoelectronic properties are attained by optimizing the molecular passivation treatments. These benefits are translated into significant enhancements of the power conversion efficiencies to 19.3%, as well as improved environmental and thermal stability of solar cells. The passivated devices without encapsulation degrade only by ≈13% after 40 d of exposure in 50% relative humidity at room temperature, and only ≈10% after 24 h at 80 °C in controlled environment.
TL;DR: Two new series of hybrid two-dimensional (2D) perovskites that adopt the Dion-Jacobson (DJ) structure type are presented, which are the first complete homologous series reported in halide perovkite chemistry.
Abstract: The three-dimensional hybrid organic–inorganic perovskites have shown huge potential for use in solar cells and other optoelectronic devices. Although these materials are under intense investigation, derivative materials with lower dimensionality are emerging, offering higher tunability of physical properties and new capabilities. Here, we present two new series of hybrid two-dimensional (2D) perovskites that adopt the Dion–Jacobson (DJ) structure type, which are the first complete homologous series reported in halide perovskite chemistry. Lead iodide DJ perovskites adopt a general formula A′An–1PbnI3n+1 (A′ = 3-(aminomethyl)piperidinium (3AMP) or 4-(aminomethyl)piperidinium (4AMP), A = methylammonium (MA)). These materials have layered structures where the stacking of inorganic layers is unique as they lay exactly on top of another. With a slightly different position of the functional group in the templating cation 3AMP and 4AMP, the as-formed DJ perovskites show different optical properties, with the 3A...
TL;DR: In this Review, recent progresses in efficient and stable perovskite solar cells using SnO2 as ETL are summarized.
Abstract: The highest power conversion efficiency of perovskite solar cells is beyond 22%. Charge transport layers are found to be critical for device performance and stability. A traditional electron transport layer (ETL), such as TiO2 , is not very efficient for charge extraction at the interface, especially in planar structure. In addition, the devices using TiO2 suffer from serious degradation under ultraviolet illumination. SnO2 owns a better band alignment with the perovskite absorption layer and high electron mobility, which is helpful for electron extraction. In this Review, recent progresses in efficient and stable perovskite solar cells using SnO2 as ETL are summarized.
TL;DR: In this paper, the authors analyzed perovskite solar cells with different architectures (planar, mesoporous, HTL-free), employing temperature dependent measurements (currentvoltage, light intensity, electroluminescence) of the ideality factor to identify dominating recombination processes that limit the open-circuit voltage (Voc).
Abstract: Metal halide perovskite absorber materials are about to emerge as a high-efficiency photovoltaic technology. At the same time, they are suitable for high-throughput manufacturing characterized by a low energy input and abundant low-cost materials. However, a further optimization of their efficiency, stability and reliability demands a more detailed optoelectronic characterization and understanding of losses including their evolution with time. In this work, we analyze perovskite solar cells with different architectures (planar, mesoporous, HTL-free), employing temperature dependent measurements (current–voltage, light intensity, electroluminescence) of the ideality factor to identify dominating recombination processes that limit the open-circuit voltage (Voc). We find that in thoroughly-optimized, high-Voc (≈1.2 V) devices recombination prevails through defects in the perovskite. On the other hand, irreversible degradation at elevated temperature is caused by the introduction of broad tail states originating from an external source (e.g. metal electrode). Light-soaking is another effect decreasing performance, though reversibly. Based on FTPS measurements, this degradation is attributed to the generation of surface defects becoming a new source of non-radiative recombination. We conclude that improving long-term stability needs to focus on adjacent layers, whereas a further optimization of efficiency of top-performing devices requires understanding of the defect physics of the nanocrystalline perovskite absorber. Finally, our work provides guidelines for the design of further dedicated studies to correctly interpret the diode ideality factor and decrease recombination losses.
TL;DR: Solar cells based on metal halide perovskites continue to approach their theoretical performance limits thanks to worldwide research efforts, and mastering the materials properties and addressing stability may allow this technology to bring profound transformations to the electric power generation industry.
Abstract: Solar cells based on metal halide perovskites continue to approach their theoretical performance limits thanks to worldwide research efforts. Mastering the materials properties and addressing stability may allow this technology to bring profound transformations to the electric power generation industry.
TL;DR: Deng et al. as discussed by the authors used amphoteric choline surfactants to blade-coat perovskite thin films, reaching module efficiencies of 15.3% and 14.6% measured at aperture areas of 33.0 cm2 and 57.2 cm2, respectively.
Abstract: Novel photovoltaic technologies such as perovskites hold the promise of a reduced levelized cost of electricity, but the low-cost potential depends on the ability to scale-up solution-based deposition. So far, complex fluid dynamics have limited the solution deposition of uniform pinhole-free organic–inorganic perovskite thin films over large areas. Here, we show that very small amounts (tens of parts per million) of surfactants (for example, l-α-Phosphatidylcholine) dramatically alter the fluid drying dynamics and increase the adhesion of the perovskite ink to the underlying non-wetting charge transport layer. The additives enable blading of smooth perovskite films at a coating rate of 180 m h–1 with root-mean-square roughness of 14.5 nm over 1 cm. The surfactants also passivate charge traps, resulting in efficiencies over 20% for small-area solar cells. Fast blading in air of perovskite films results in stabilized module efficiencies of 15.3% and 14.6% measured at aperture areas of 33.0 cm2 and 57.2 cm2, respectively. Scaling up perovskite film deposition necessitates controlling the film formation dynamics. Here, Deng et al. use amphoteric choline surfactants to blade-coat well-passivated films, reaching module efficiencies of ~15% for aperture areas up to 57 cm2.
TL;DR: A universal potassium passivation strategy is developed to improve the quality of slot-die printed tin oxide electron transport layers and demonstrate highly efficient and hysteresis-free flexible devices.
Abstract: Perovskite solar cells (PSCs) have reached an impressive efficiency over 23%. One of its promising characteristics is the low-cost solution printability, especially for flexible solar cells. However, printing large area uniform electron transport layers on rough and soft plastic substrates without hysteresis is still a great challenge. Herein, we demonstrate slot-die printed high quality tin oxide films for high efficiency flexible PSCs. The inherent hysteresis induced by the tin oxide layer is suppressed using a universal potassium interfacial passivation strategy regardless of fabricating methods. Results show that the potassium cations, not the anions, facilitate the growth of perovskite grains, passivate the interface, and contribute to the enhanced efficiency and stability. The small size flexible PSCs achieve a high efficiency of 17.18% and large size (5 × 6 cm2) flexible modules obtain an efficiency over 15%. This passivation strategy has shown great promise for pursuing high performance large area flexible PSCs.
TL;DR: In this paper, a 2D-3D perovskite stacking-layered architecture was designed by in situ growing 2D PEA(2)PbI(4) capping layers on top of 3D PbI film, which drastically improved the stability of PSCs without compromising their high performance.
Abstract: 2D halide perovskites have recently been recognized as a promising avenue in perovskite solar cells (PSCs) in terms of encouraging stability and defect passivation effect. However, the efficiency (less than 15%) of ultrastable 2D Ruddlesden-Popper PSCs still lag far behind their traditional 3D perovskite counterparts. Here, a rationally designed 2D-3D perovskite stacking-layered architecture by in situ growing 2D PEA(2)PbI(4) capping layers on top of 3D perovskite film, which drastically improves the stability of PSCs without compromising their high performance, is reported. Such a 2D perovskite capping layer induces larger Fermi-level splitting in the 2D-3D perovskite film under light illumination, resulting in an enhanced open-circuit voltage (V-oc) and thus a higher efficiency of 18.51% in the 2D-3D PSCs. Time-resolved photoluminescence decay measurements indicate the facilitated hole extraction in the 2D-3D stacking-layered perovskite films, which is ascribed to the optimized energy band alignment and reduced nonradiative recombination at the subgap states. Benefiting from the high moisture resistivity as well as suppressed ion migration of the 2D perovskite, the 2D-3D PSCs show significantly improved long-term stability, retaining nearly 90% of the initial power conversion efficiency after 1000 h exposure in the ambient conditions with a high relative humidity level of 60 +/- 10%.
TL;DR: This one-step bifunctional stabilization of perovskite through gradient halide doping and surface organic cation passivation presents a novel and promising strategy to design stable and high performance all-inorganic lead halide.
Abstract: The all-inorganic α-CsPbI3 perovskite with the most suitable band gap faces serious challenges of low phase stability and high moisture sensitivity. We discover that a simple phenyltrimethylammonium bromide (PTABr) post-treatment could achieve a bifunctional stabilization including both gradient Br doping (or alloying) and surface passivation. The PTABr treatment on CsPbI3 only induces less than 5 nm blue shift in UV–vis absorbance but significantly stabilize the perovskite phase with much better stability. Finally, the highly stable PTABr treated CsPbI3 based perovskite solar cells exhibit a reproducible photovoltaic performance with a champion efficiency up to 17.06% and stable output of 16.3%. Therefore, this one-step bifunctional stabilization of perovskite through gradient halide doping and surface organic cation passivation presents a novel and promising strategy to design stable and high performance all-inorganic lead halide.
TL;DR: Correlated, in situ structural and device characterizations reveal that light-induced lattice expansion benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5 to 20.5%.
Abstract: Light-induced structural dynamics plays a vital role in the physical properties, device performance, and stability of hybrid perovskite–based optoelectronic devices. We report that continuous light illumination leads to a uniform lattice expansion in hybrid perovskite thin films, which is critical for obtaining high-efficiency photovoltaic devices. Correlated, in situ structural and device characterizations reveal that light-induced lattice expansion benefits the performances of a mixed-cation pure-halide planar device, boosting the power conversion efficiency from 18.5 to 20.5%. The lattice expansion leads to the relaxation of local lattice strain, which lowers the energetic barriers at the perovskite-contact interfaces, thus improving the open circuit voltage and fill factor. The light-induced lattice expansion did not compromise the stability of these high-efficiency photovoltaic devices under continuous operation at full-spectrum 1-sun (100 milliwatts per square centimeter) illumination for more than 1500 hours.
TL;DR: The fabrication of phase-pure formamidinium-lead tri-iodide perovskite films with excellent optoelectronic quality and stability is reported with an order of magnitude enhanced photoluminescence lifetime.
Abstract: Compositional engineering has been used to overcome difficulties in fabricating high-quality phase-pure formamidinium perovskite films together with its ambient instability. However, this comes alongside an undesirable increase in bandgap that sacrifices the device photocurrent. Here we report the fabrication of phase-pure formamidinium-lead tri-iodide perovskite films with excellent optoelectronic quality and stability. Incorporation of 1.67 mol% of 2D phenylethylammonium lead iodide into the precursor solution enables the formation of phase-pure formamidinium perovskite with an order of magnitude enhanced photoluminescence lifetime. The 2D perovskite spontaneously forms at grain boundaries to protect the formamidinium perovskite from moisture and suppress ion migration. A stabilized power conversion efficiency (PCE) of 20.64% (certified stabilized PCE of 19.77%) is achieved with a short-circuit current density exceeding 24 mA cm-2 and an open-circuit voltage of 1.130 V, corresponding to a loss-in-potential of 0.35 V, and significantly enhanced operational stability.
TL;DR: Wang et al. show a controlled drying process to make phase stable and highly efficient solar cells with power conversion efficiency of 15.7%, which is the highest efficiency reported for inorganic perovskite solar cells up to now.
Abstract: Inorganic halide perovskites such as cesium lead halide are promising due to their excellent thermal stability. Cesium lead iodide (CsPbI3) has a bandgap of 1.73 eV and is very suitable for making efficient tandem solar cells, either with low-bandgap perovskite or silicon. However, the phase instability of CsPbI3 is hindering the further optimization of device performance. Here, we show that high quality and stable α-phase CsPbI3 film is obtained via solvent-controlled growth of the precursor film in a dry environment. A 15.7% power conversion efficiency of CsPbI3 solar cells is achieved, which is the highest efficiency reported for inorganic perovskite solar cells up to now. And more importantly, the devices can tolerate continuous light soaking for more than 500 h without efficiency drop.
TL;DR: In this article, a polyvinylpyrrolidone (PVP)-induced surface passivation engineering is reported to synthesize extra-long-term stable cubic cesium lead iodides (CsPbI3) for commercial perovskite solar cells.
Abstract: Owing to inevitable thermal/moisture instability for organic–inorganic hybrid perovskites, pure inorganic perovskite cesium lead halides with both inherent stability and prominent photovoltaic performance have become research hotspots as a promising candidate for commercial perovskite solar cells. However, it is still a serious challenge to synthesize desired cubic cesium lead iodides (CsPbI3) with superior photovoltaic performance for its thermodynamically metastable characteristics. Herein, polymer poly-vinylpyrrolidone (PVP)-induced surface passivation engineering is reported to synthesize extra-long-term stable cubic CsPbI3. It is revealed that acylamino groups of PVP induce electron cloud density enhancement on the surface of CsPbI3, thus lowering surface energy, conducive to stabilize cubic CsPbI3 even in micrometer scale. The cubic-CsPbI3 PSCs exhibit extra-long carrier diffusion length (over 1.5 μm), highest power conversion efficiency of 10.74% and excellent thermal/moisture stability. This result provides important progress towards understanding of phase stability in realization of large-scale preparations of efficient and stable inorganic PSCs.
TL;DR: A general scaling law is proposed to determine the binding energy of excitons in perovskite quantum wells of any layer thickness to solve the fundamental questions concerning the nature of optical resonances and their scaling with quantum well thickness.
Abstract: Ruddlesden–Popper halide perovskites are 2D solution-processed quantum wells with a general formula A2A’n-1M
n
X3n+1, where optoelectronic properties can be tuned by varying the perovskite layer thickness (n-value), and have recently emerged as efficient semiconductors with technologically relevant stability. However, fundamental questions concerning the nature of optical resonances (excitons or free carriers) and the exciton reduced mass, and their scaling with quantum well thickness, which are critical for designing efficient optoelectronic devices, remain unresolved. Here, using optical spectroscopy and 60-Tesla magneto-absorption supported by modeling, we unambiguously demonstrate that the optical resonances arise from tightly bound excitons with both exciton reduced masses and binding energies decreasing, respectively, from 0.221 m0 to 0.186 m0 and from 470 meV to 125 meV with increasing thickness from n equals 1 to 5. Based on this study we propose a general scaling law to determine the binding energy of excitons in perovskite quantum wells of any layer thickness. Hybrid 2D layered perovskites are solution-processed quantum wells whose optoelectronic properties are tunable by varying the thickness of the inorganic slab. Here Blancon et al. work out a general behavior for dependence of the excitonic properties in layered 2D perovskites.
TL;DR: In this paper, a new class of high-entropy perovskite oxides (i.e., multiple-cation solid solutions with high configurational entropies) has been synthesized.
TL;DR: In this article, the effect of local lattice strain on vacancy formation was investigated in single-cation/halide perovskites and the authors showed that judiciously selected dopants can maximize the formation energy of defects responsible for degradation.
Abstract: The degradation of perovskite solar cells in the presence of trace water and oxygen poses a challenge for their commercial impact given the appreciable permeability of cost-effective encapsulants. Point defects were recently shown to be a major source of decomposition due to their high affinity for water and oxygen molecules. Here, we report that, in single-cation/halide perovskites, local lattice strain facilitates the formation of vacancies and that cation/halide mixing suppresses their formation via strain relaxation. We then show that judiciously selected dopants can maximize the formation energy of defects responsible for degradation. Cd-containing cells show an order of magnitude enhanced unencapsulated stability compared to state-of-art mixed perovskite solar cells, for both shelf storage and maximum power point operation in ambient air at a relative humidity of 50%. We conclude by testing the generalizability of the defect engineering concept, demonstrating both vacancy-formation suppressors (such as Zn) and promoters (such as Hg). Despite their high efficiencies, perovskite solar cells still suffer from degradation issues that impede their practical deployment. Saidaminov et al. explore the effect of local lattice strain on vacancy formation and show that careful choice of dopants plays a key role, enhancing the device stability.