Showing papers by "Michael Grätzel published in 2017"
TL;DR: Because photocurrents are near the theoretical maximum, the focus is on efforts to increase open-circuit voltage by means of improving charge-selective contacts and charge carrier lifetimes in perovskites via processes such as ion tailoring.
Abstract: The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1% in a few years' time. At this stage of their development, the key issues concern how to achieve further improvements in efficiency and long-term stability. We review recent developments in the quest to improve the current state of the art. Because photocurrents are near the theoretical maximum, our focus is on efforts to increase open-circuit voltage by means of improving charge-selective contacts and charge carrier lifetimes in perovskites via processes such as ion tailoring. The challenges associated with long-term perovskite solar cell device stability include the role of testing protocols, ionic movement affecting performance metrics over extended periods of time, and determination of the best ways to counteract degradation mechanisms.
1,371 citations
TL;DR: Th Thin CuSCN films can replace organic hole-transporting layers that limit thermal stability of devices and demonstrate PSCs that achieve stabilized efficiencies exceeding 20% with copper(I) thiocyanate (CuSCN) as the hole extraction layer.
Abstract: Perovskite solar cells (PSCs) with efficiencies greater than 20% have been realized only with expensive organic hole-transporting materials. We demonstrate PSCs that achieve stabilized efficiencies exceeding 20% with copper(I) thiocyanate (CuSCN) as the hole extraction layer. A fast solvent removal method enabled the creation of compact, highly conformal CuSCN layers that facilitate rapid carrier extraction and collection. The PSCs showed high thermal stability under long-term heating, although their operational stability was poor. This instability originated from potential-induced degradation of the CuSCN/Au contact. The addition of a conductive reduced graphene oxide spacer layer between CuSCN and gold allowed PSCs to retain >95% of their initial efficiency after aging at a maximum power point for 1000 hours under full solar intensity at 60°C. Under both continuous full-sun illumination and thermal stress, CuSCN-based devices surpassed the stability of spiro-OMeTAD–based PSCs.
1,210 citations
TL;DR: The perovskite solar cells (PSCs) have attracted much attention because of their rapid rise to 22% efficiencies as discussed by the authors, which could revolutionize the photovoltaic industry.
Abstract: Perovskite solar cells (PSCs) have attracted much attention because of their rapid rise to 22% efficiencies. Here, we review the rapid evolution of PSCs as they enter a new phase that could revolutionize the photovoltaic industry. In particular, we describe the properties that make perovskites so remarkable, and the current understanding of the PSC device physics, including the operation of state-of-the-art solar cells with efficiencies above 20%. The extraordinary progress of long-term stability is discussed and we provide an outlook on what the future of PSCs might soon bring the photovoltaic community. Some challenges remain in terms of reducing non-radiative recombination and increasing conductivity of the different device layers, and these will be discussed in depth in this review.
924 citations
TL;DR: In this article, a dye-sensitized solar cell (DSC) that achieves very high power-conversion efficiencies (PCEs) under ambient light conditions is presented.
Abstract: Solar cells that operate efficiently under indoor lighting are of great practical interest as they can serve as electric power sources for portable electronics and devices for wireless sensor networks or the Internet of Things. Here, we demonstrate a dye-sensitized solar cell (DSC) that achieves very high power-conversion efficiencies (PCEs) under ambient light conditions. Our photosystem combines two judiciously designed sensitizers, coded D35 and XY1, with the copper complex Cu(II/I)(tmby) as a redox shuttle (tmby, 4,4′,6,6′-tetramethyl-2,2′-bipyridine), and features a high open-circuit photovoltage of 1.1 V. The DSC achieves an external quantum efficiency for photocurrent generation that exceeds 90% across the whole visible domain from 400 to 650 nm, and achieves power outputs of 15.6 and 88.5 μW cm–2 at 200 and 1,000 lux, respectively, under illumination from a model Osram 930 warm-white fluorescent light tube. This translates into a PCE of 28.9%. A dye-sensitized solar cell that has been designed for efficient operation under indoor lighting could offer a convenient means for powering the Internet of Things.
801 citations
TL;DR: A new deposition route for methyl ammonium lead halide perovskite films that does not rely on use of a common solvent or vacuum, and relies on the rapid conversion of amine complex precursors to perovkite films, followed by a pressure application step to overcome the substantial reduction in power conversion efficiency when a small device is scaled up.
Abstract: A new deposition method for solar-panel polycrystalline perovskite thin films enables the production of large-area uniform films and avoids the need for common solvents or vacuum. Hybrid inorganic–organic perovskites are the most likely materials to replace silicon as absorber layers for solar cells, but issues with stability and scaling-up thin films mean that large-scale production is not yet possible. Liyuan Han and colleagues have developed a new deposition method for polycrystalline thin films that does not rely on spin- or drip-coating precursors in solvent or on vacuum deposition, and is therefore more amenable to larger-area films than are previous techniques. The procedure uses gaseous precursors and application of pressure, and has enabled a device with an area of 36 square centimetres to be certified at 12.1 per cent power conversion efficiency. Recent advances in the use of organic–inorganic hybrid perovskites for optoelectronics have been rapid, with reported power conversion efficiencies of up to 22 per cent for perovskite solar cells1,2,3,4,5,6,7,8,9. Improvements in stability have also enabled testing over a timescale of thousands of hours10,11,12,13,14. However, large-scale deployment of such cells will also require the ability to produce large-area, uniformly high-quality perovskite films. A key challenge is to overcome the substantial reduction in power conversion efficiency when a small device is scaled up: a reduction from over 20 per cent to about 10 per cent is found15,16,17,18,19,20,21 when a common aperture area of about 0.1 square centimetres is increased to more than 25 square centimetres. Here we report a new deposition route for methyl ammonium lead halide perovskite films that does not rely on use of a common solvent1,2,4,5,6,7,8,9,10,11,12,13,14,15 or vacuum3: rather, it relies on the rapid conversion of amine complex precursors to perovskite films, followed by a pressure application step. The deposited perovskite films were free of pin-holes and highly uniform. Importantly, the new deposition approach can be performed in air at low temperatures, facilitating fabrication of large-area perovskite devices. We reached a certified power conversion efficiency of 12.1 per cent with an aperture area of 36.1 square centimetres for a mesoporous TiO2-based perovskite solar module architecture.
583 citations
TL;DR: It is discovered that a small amount of two-dimensional EDAPbI4 perovskite containing the ethylenediamine (EDA) cation stabilizes the α-CsPbI3 to avoid the undesirable formation of the nonperovskites δ phase.
Abstract: Among various all-inorganic halide perovskites exhibiting better stability than organic-inorganic halide perovskites, α-CsPbI3 with the most suitable band gap for tandem solar cell application faces an issue of phase instability under ambient conditions We discovered that a small amount of two-dimensional (2D) EDAPbI4 perovskite containing the ethylenediamine (EDA) cation stabilizes the α-CsPbI3 to avoid the undesirable formation of the nonperovskite δ phase Moreover, not only the 2D perovskite of EDAPbI4 facilitate the formation of α-CsPbI3 perovskite films exhibiting high phase stability at room temperature for months and at 100°C for >150 hours but also the α-CsPbI3 perovskite solar cells (PSCs) display highly reproducible efficiency of 118%, a record for all-inorganic lead halide PSCs Therefore, using the bication EDA presents a novel and promising strategy to design all-inorganic lead halide PSCs with high performance and reliability
528 citations
TL;DR: In this article, the authors demonstrate that ionic defects, migrating on timescales significantly longer (above 103 s) than what has so far been explored (from 10−1 to 102 s), abate the initial efficiency by 10−15% after several hours of operation at the maximum power point.
Abstract: Perovskites have been demonstrated in solar cells with a power conversion efficiency of well above 20%, which makes them one of the strongest contenders for next generation photovoltaics. While there are no concerns about their efficiency, very little is known about their stability under illumination and load. Ionic defects and their migration in the perovskite crystal lattice are some of the most alarming sources of degradation, which can potentially prevent the commercialization of perovskite solar cells (PSCs). In this work, we provide direct evidence of electric field-induced ionic defect migration and we isolate their effect on the long-term performance of state-of-the-art devices. Supported by modelling, we demonstrate that ionic defects, migrating on timescales significantly longer (above 103 s) than what has so far been explored (from 10−1 to 102 s), abate the initial efficiency by 10–15% after several hours of operation at the maximum power point. Though these losses are not negligible, we prove that the initial efficiency is fully recovered when leaving the device in the dark for a comparable amount of time. We verified this behaviour over several cycles resembling day/night phases, thus probing the stability of PSCs under native working conditions. This unusual behaviour reveals that research and industrial standards currently in use to assess the performance and the stability of solar cells need to be adjusted for PSCs. Our work paves the way for much needed new testing protocols and figures of merit specifically designed for PSCs.
487 citations
TL;DR: Schreier et al. as discussed by the authors introduced atomic layer deposition of SnO2 on CuO nanowires as a means for changing the wide product distribution of CuO-derived CO2 reduction electrocatalysts to yield predominantly CO.
Abstract: The solar-driven electrochemical reduction of CO2 to fuels and chemicals provides a promising way for closing the anthropogenic carbon cycle. However, the lack of selective and Earth-abundant catalysts able to achieve the desired transformation reactions in an aqueous matrix presents a substantial impediment as of today. Here we introduce atomic layer deposition of SnO2 on CuO nanowires as a means for changing the wide product distribution of CuO-derived CO2 reduction electrocatalysts to yield predominantly CO. The activity of this catalyst towards oxygen evolution enables us to use it both as the cathode and anode for complete CO2 electrolysis. In the resulting device, the electrodes are separated by a bipolar membrane, allowing each half-reaction to run in its optimal electrolyte environment. Using a GaInP/GaInAs/Ge photovoltaic we achieve the solar-driven splitting of CO2 into CO and oxygen with a bifunctional, sustainable and all Earth-abundant system at an efficiency of 13.4%. Electrochemical reduction of CO2 to CO is a route to synthesize fuels, but cheaper and more selective catalysts are required. Using a cell equipped with a bipolar membrane and the same Earth-abundant electrocatalyst at each electrode, Schreier et al. selectively produce CO, powered by a triple-junction photovoltaic.
384 citations
TL;DR: In this paper, a high quality perovskite absorber with a horizontal grain size up to 3 μm and a lateral size equal to the film thickness was prepared by the synergistic effect of a H2O additive and DMF vapor treatment via a two-step spin coating method.
Abstract: A high quality thick (500 nm) CH3NH3PbI3 perovskite absorber with a horizontal grain size up to 3 μm and a lateral size equal to the film thickness was prepared by the synergistic effect of a H2O additive and DMF vapor treatment via a two-step spin coating method. The inverted (p–i–n) cell based on this high-quality thick perovskite film achieves a high power conversion efficiency of 20.1%. The cell shows no current hysteresis and is stable in inert and ambient atmospheres with appropriate encapsulation. H2O helps MAI to penetrate into the thick PbI2 to form a thick film with a pure MAPbI3 phase and produces bigger gains by slowing down the perovskite crystallization rate. It can also cooperate with DMF to control the dissolution of perovskite grains during DMF vapor post treatment. As a result, large multi-crystalline perovskite grains without observable holes and creases are formed when DMF and H2O were removed during the following heating process. The synergistic effect of H2O and DMF was evidenced by SEM images and GIWXRD patterns taken simultaneously. This synergistic strategy for preparing a high-quality, thick perovskite film was extended to fabricate a large-area MAPbI3 film (1.3 cm2 and 11.25 cm2 for the cell and mini-module, respectively) to realize an efficiency of 16.7 and 15.4%.
354 citations
TL;DR: A nanostructured carbon layer is designed to suppress the diffusion of ions/molecules within perovskite solar cells, an important degradation process in the device, and this nanocarbon layer benefited the diffusionof electron charge carriers to enable a high-energy conversion efficiency.
Abstract: Long-term stability is crucial for the future application of perovskite solar cells, a promising low-cost photovoltaic technology that has rapidly advanced in the recent years. Here, we designed a nanostructured carbon layer to suppress the diffusion of ions/molecules within perovskite solar cells, an important degradation process in the device. Furthermore, this nanocarbon layer benefited the diffusion of electron charge carriers to enable a high-energy conversion efficiency. Finally, the efficiency on a perovskite solar cell with an aperture area of 1.02 cm2, after a thermal aging test at 85 °C for over 500 h, or light soaking for 1,000 h, was stable of over 15% during the entire test. The present diffusion engineering of ions/molecules and photo generated charges paves a way to realizing long-term stable and highly efficient perovskite solar cells. Ion migration in perovskite solar cells are known to cause hysteresis and instability. Biet al., report a charge extraction layer based on graphene, fullerenes and carbon quantum dots which suppresses ion diffusion and enhances charge carrier diffusion leading to efficient devices with improved stability.
335 citations
TL;DR: A fullerene derivative is purified from an as-produced bis-phenyl-C61 -butyric acid methyl ester mixture and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method, achieving better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM.
Abstract: A fullerene derivative (α-bis-PCBM) is purified from an as-produced bis-phenyl-C61 -butyric acid methyl ester (bis-[60]PCBM) isomer mixture by preparative peak-recycling, high-performance liquid chromatography, and is employed as a templating agent for solution processing of metal halide perovskite films via an antisolvent method. The resulting α-bis-PCBM-containing perovskite solar cells achieve better stability, efficiency, and reproducibility when compared with analogous cells containing PCBM. α-bis-PCBM fills the vacancies and grain boundaries of the perovskite film, enhancing the crystallization of perovskites and addressing the issue of slow electron extraction. In addition, α-bis-PCBM resists the ingression of moisture and passivates voids or pinholes generated in the hole-transporting layer. As a result, a power conversion efficiency (PCE) of 20.8% is obtained, compared with 19.9% by PCBM, and is accompanied by excellent stability under heat and simulated sunlight. The PCE of unsealed devices dropped by less than 10% in ambient air (40% RH) after 44 d at 65 °C, and by 4% after 600 h under continuous full-sun illumination and maximum power point tracking, respectively.
TL;DR: The atomic-level nature of Cs and Rb incorporation into the perovskite lattice of FA-based materials is elucidated and fundamental understanding of previously reported excellent photovoltaic parameters in these systems and their superior stability is provided.
Abstract: Hybrid (organic-inorganic) multi-cation lead halide perovskites hold promise for a new generation of easily processable solar cells. Best performing compositions to date are multiple-cation solid alloys of formamidinium (FA), methylammonium (MA), cesium and rubidium lead halides which provide power conversion efficiencies up to around 22%. Here, we elucidate the atomic level nature of Cs and Rb incorporation into the perovskite lattice of FA-based materials. We use 133Cs, 87Rb, 39K, 13C and 14N solid-state MAS NMR to probe microscopic composition of Cs-, Rb-, K-, MA- and FA-containing phases in double-, triple- and quadruple-cation lead halides in bulk and in a thin film. Contrary to previous reports, we have found no proof of Rb or K incorporation into the 3D perovskite lattice in these systems. We also show that the structure of bulk mechanochemical perovskites bears close resemblance to that of thin films, making them a good benchmark for structural studies. These findings provide fundamental understan...
TL;DR: In this article, the authors investigated the recombination at different interfaces in a perovskite solar cells, including the charge selective contacts and the effect of grain boundaries, and showed that a further suppression of non-radiative recombination is possible for an all-low-temperature PSC, to yield a very low loss-in-potential similar to GaAs, and thus paving the way towards higher than 22% efficiencies.
Abstract: With close to 100% internal quantum efficiency over the absorption spectrum, photocurrents in perovskite solar cells (PSCs) are at their practical limits. It is therefore imperative to improve open-circuit voltages (VOC) in order to go beyond the current 100 mV loss-in-potential. Identifying and suppressing recombination bottlenecks in the device stack will ultimately drive the voltages up. In this work, we investigate in depth the recombination at the different interfaces in a PSC, including the charge selective contacts and the effect of grain boundaries. We find that the density of grain boundaries and the use of tunneling layers in a highly efficient PSC do not modify the recombination dynamics at 1 sun illumination. Instead, the recombination is strongly dominated by the dopants in the hole transporting material (HTM), spiro-OMeTAD and PTAA. The reduction of doping concentrations for spiro-OMeTAD yielded VOC's as high as 1.23 V in contrast to PTAA, which systematically showed slightly lower voltages. This work shows that a further suppression of non-radiative recombination is possible for an all-low-temperature PSC, to yield a very low loss-in-potential similar to GaAs, and thus paving the way towards higher than 22% efficiencies.
TL;DR: Apart from leading the current PV efficiency race, these new perovskite materials exhibit intense electroluminescence and an extraordinarily high stability under heat and light stress.
Abstract: Recently, metal halide perovskite solar cells (PSCs) of the general formular ABX3 where A is a monovalent cation, that is, methylammonium (MA) CH3NH3+•, formamidinium CH2(NH2)2+, Cs+, or Rb+, B stands for Pb(II) or Sn(II), and X for iodide or bromide have achieved solar to electric power conversion efficiencies (PCEs) above 22%, exceeding the efficiency of the present market leader polycrystalline silicon while using 1000 times less light harvesting material and simple solution processing for their fabrication. The top performing devices all employ formulations containing a mixture of up to four A cations and iodide as well as a small fraction of bromide as anion, whose emergence will be described in this Commentary. Apart from leading the current PV efficiency race, these new perovskite materials exhibit intense electroluminescence and an extraordinarily high stability under heat and light stress.
TL;DR: This work demonstrates efficient room temperature hot-electrons extraction by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films and enables fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells.
Abstract: Hot-carrier solar cells can overcome the Shockley-Queisser limit by harvesting excess energy from hot carriers. Inorganic semiconductor nanocrystals are considered prime candidates. However, hot-carrier harvesting is compromised by competitive relaxation pathways (for example, intraband Auger process and defects) that overwhelm their phonon bottlenecks. Here we show colloidal halide perovskite nanocrystals transcend these limitations and exhibit around two orders slower hot-carrier cooling times and around four times larger hot-carrier temperatures than their bulk-film counterparts. Under low pump excitation, hot-carrier cooling mediated by a phonon bottleneck is surprisingly slower in smaller nanocrystals (contrasting with conventional nanocrystals). At high pump fluence, Auger heating dominates hot-carrier cooling, which is slower in larger nanocrystals (hitherto unobserved in conventional nanocrystals). Importantly, we demonstrate efficient room temperature hot-electrons extraction (up to ∼83%) by an energy-selective electron acceptor layer within 1 ps from surface-treated perovskite NCs thin films. These insights enable fresh approaches for extremely thin absorber and concentrator-type hot-carrier solar cells. Harvesting excess energy from above-band gap photons could lead to solar cells which exceed conventional efficiency limits. Liet al., study hot carrier cooling in hybrid perovskite materials with reduced dimensionality using transient absorption spectroscopy and demonstrate efficient hot-electron extraction in such systems.
TL;DR: Iodine ions are unambiguously shown to be the mobile species in CH3NH3PbI3, with iodine vacancies shown to represent the mechanistic centers under equilibrium conditions, and local variations of the iodine stoichiometry may be fast and enable light effects on ion transport.
Abstract: By applying a multitude of experimental techniques including 1 H, 14 N, 207 Pb NMR and 127 I NMR/NQR, tracer diffusion, reaction cell and doping experiments, as well as stoichiometric variation, conductivity, and polarization experiments, iodine ions are unambiguously shown to be the mobile species in CH3 NH3 PbI3 , with iodine vacancies shown to represent the mechanistic centers under equilibrium conditions Pb2+ and CH3 NH3+ ions do not significantly contribute to the long range transport (upper limits for their contributions are given), whereby the latter exhibit substantial local motion The decisive electronic contribution to the mixed conductivity in the experimental window stems from electron holes As holes can be associated with iodine orbitals, local variations of the iodine stoichiometry may be fast and enable light effects on ion transport
TL;DR: It is shown that light has a strong influence on the rate of perovskite formation and on film morphology in both of the main deposition methods currently used: sequential deposition and the anti-solvent method.
Abstract: Optimizing the morphology of metal halide perovskite films is an important way to improve the performance of solar cells when these materials are used as light harvesters, because film homogeneity is correlated with photovoltaic performance. Many device architectures and processing techniques have been explored with the aim of achieving high-performance devices, including single-step deposition, sequential deposition and anti-solvent methods. Earlier studies have looked at the influence of reaction conditions on film quality, such as the concentration of the reactants and the reaction temperature. However, the precise mechanism of the reaction and the main factors that govern it are poorly understood. The consequent lack of control is the main reason for the large variability observed in perovskite morphology and the related solar-cell performance. Here we show that light has a strong influence on the rate of perovskite formation and on film morphology in both of the main deposition methods currently used: sequential deposition and the anti-solvent method. We study the reaction of a metal halide (lead iodide) with an organic compound (methylammonium iodide) using confocal laser scanning fluorescence microscopy and scanning electron microscopy. The lead iodide crystallizes before the intercalation of methylammonium iodide commences, producing the methylammonium lead iodide perovskite. We find that the formation of perovskite via such a sequential deposition is much accelerated by light. The influence of light on morphology is reflected in a doubling of solar-cell efficiency. Conversely, using the anti-solvent method to form methyl ammonium lead iodide perovskite in a single step from the same starting materials, we find that the best photovoltaic performance is obtained when films are produced in the dark. The discovery of light-activated crystallization not only identifies a previously unknown source of variability in opto-electronic properties, but also opens up new ways of tuning morphology and structuring perovskites for various applications.
TL;DR: A record 11% stable solid-state dye-sensitized solar cell under standard air mass 1.5 global is reported using a hole-transport material composed of a blend of amorphous Cu(II/I) conductors that conduct holes by rapid hopping infiltrated in a 6.5 μm-thick mesoscopic TiO2 scaffold.
Abstract: Solid-state dye-sensitized solar cells currently suffer from issues such as inadequate nanopore filling, low conductivity and crystallization of hole-transport materials infiltrated in the mesoscop ...
TL;DR: In this article, two novel molecular hole-transporting materials (HTMs) using the thiophene core were designed and synthesized (Z25 and Z26), and the perovskite solar cells based on Z26 exhibited a remarkable overall power conversion efficiency (PCE) of 20.1%, which is comparable to 20.6% obtained with spiroOMeTAD.
TL;DR: During the 140 h experiment, the solar cells with the Au electrode experience a dramatic, irreversible efficiency loss, rendering them effectively nonoperational, whereas the SWCNT-contacted devices show only a small linear efficiency loss with an extrapolated lifetime of 580 h.
Abstract: Mixed ion perovskite solar cells (PSC) are manufactured with a metal-free hole contact based on press-transferred single-walled carbon nanotube (SWCNT) film infiltrated with 2,2,7,-7-tetrakis(N,N-di-p-methoxyphenylamine)-9,90-spirobifluorene (Spiro-OMeTAD). By means of maximum power point tracking, their stabilities are compared with those of standard PSCs employing spin-coated Spiro-OMeTAD and a thermally evaporated Au back contact, under full 1 sun illumination, at 60 °C, and in a N2 atmosphere. During the 140 h experiment, the solar cells with the Au electrode experience a dramatic, irreversible efficiency loss, rendering them effectively nonoperational, whereas the SWCNT-contacted devices show only a small linear efficiency loss with an extrapolated lifetime of 580 h.
TL;DR: The first quantitative, cation-specific data on cation reorientation dynamics in hybrid mixed-cation formamidinium (FA)/methylammonium (MA) lead halide perovskites is reported.
Abstract: Mixed-cation organic lead halide perovskites attract unfaltering attention owing to their excellent photovoltaic properties. Currently, the best performing perovskite materials contain multiple cations and provide power conversion efficiencies up to around 22%. Here, we report the first quantitative, cation-specific data on cation reorientation dynamics in hybrid mixed-cation formamidinium (FA)/methylammonium (MA) lead halide perovskites. We use 14N, 2H, 13C, and 1H solid-state MAS NMR to elucidate cation reorientation dynamics, microscopic phase composition, and the MA/FA ratio, in (MA)x(FA)1–xPbI3 between 100 and 330 K. The reorientation rates correlate in a striking manner with the carrier lifetimes previously reported for these materials and provide evidence of the polaronic nature of charge carriers in PV perovskites.
TL;DR: A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs) that show high efficiency and no hysteresis on rigid and flexible substrates, respectively.
Abstract: A new, all room-temperature solution process is developed to fabricate efficient, low-cost, and stable perovskite solar cells (PVSCs). The PVSCs show high efficiency of 17.10% and 14.19%, with no hysteresis on rigid and flexible substrates, respectively, which are the best efficiencies reported to date for PVSCs fabricated by room-temperature solution-processed techniques. The flexible PVSCs show a remarkable power-per-weight of 23.26 W g-1 .
TL;DR: The whole process of the perovskites formation and transformation from the molecular to the microstructure over relevant temperature and time scales is successfully demonstrated.
Abstract: Hybrid lead halide perovskites have emerged as high-performance photovoltaic materials with their extraordinary optoelectronic properties. In particular, the remarkable device efficiency is strongly influenced by the perovskite crystallinity and the film morphology. Here, we investigate the perovskites crystallisation kinetics and growth mechanism in real time from liquid precursor continually to the final uniform film. We utilize some advanced in situ characterisation techniques including synchrotron-based grazing incident X-ray diffraction to observe crystal structure and chemical transition of perovskites. The nano-assemble model from perovskite intermediated [PbI6]4- cage nanoparticles to bulk polycrystals is proposed to understand perovskites formation at a molecular- or nano-level. A crystallisation-depletion mechanism is developed to elucidate the periodic crystallisation and the kinetically trapped morphology at a mesoscopic level. Based on these in situ dynamics studies, the whole process of the perovskites formation and transformation from the molecular to the microstructure over relevant temperature and time scales is successfully demonstrated.
TL;DR: In this article, a synchrotron-based photoelectron spectroscopy was used to analyze the chemical composition of perovskite materials with two, three, or four monovalent cations.
Abstract: Lead-based mixed perovskite materials have emerged in the last couple of years as promising photovoltaic materials. Recently, it was shown that improved material stability can be achieved by incorporating small amounts of inorganic cations (Cs+ and Rb+), partially replacing the more common organic cations (e.g., methylammonium, MA, and formamidinium, FA). Especially, a mixed cation composition containing Rb+, Cs+, MA+, and FA+ was recently shown to have beneficial optoelectronic properties and was stable at elevated temperature. This work focuses on the composition of this material using synchrotron-based photoelectron spectroscopy. Different probing depths were considered by changing the photon energy of the X-ray source providing insights on the chemical composition and the chemical distribution near the surface of the samples. Perovskite materials containing two, three, or four monovalent cations were analyzed and compared. The presence of Cs and Rb was observed both at the sample surface and toward th...
TL;DR: This work reveals that the family of halide perovskite colloidal nanocrystals transcend these constraints with highly efficient five-photon-excited upconversion fluorescence—unprecedented for semiconductor nanocry crystals.
Abstract: Multiphoton absorption processes enable many technologically important applications, such as in vivo imaging, photodynamic therapy and optical limiting, and so on. Specifically, higher-order nonlinear absorption such as five-photon absorption offers significant advantages of greater spatial confinement, increased penetration depth, reduced autofluorescence, enhanced sensitivity and improved resolution over lower orders in bioimaging. Organic chromophores and conventional semiconductor nanocrystals are leaders in two-/three-photon absorption applications, but face considerable challenges from their small five-photon action cross-sections. Herein, we reveal that the family of halide perovskite colloidal nanocrystals transcend these constraints with highly efficient five-photon-excited upconversion fluorescence-unprecedented for semiconductor nanocrystals. Amazingly, their multidimensional type I (both conduction and valence band edges of core lie within bandgap of shell) core-shell (three-dimensional methylammonium lead bromide/two-dimensional octylammonium lead bromide) perovskite nanocrystals exhibit five-photon action cross-sections that are at least 9 orders larger than state-of-the-art specially designed organic molecules. Importantly, this family of halide perovskite nanocrystals may enable fresh approaches for next-generation multiphoton imaging applications.
TL;DR: In this paper, carbon-based perovskite solar cells are fabricated for the first time in a room temperature environment by employing inkjet infiltration of perovsite precursor ink.
Abstract: Carbon based perovskite solar cells are fabricated for the first time in a room temperature environment by employing inkjet infiltration of perovskite precursor ink. The fabricated perovskite solar cells exhibit impressive performance reproducibility with this automated method and exhibit high stability when exposed to 35 degrees C for a period of 1046 hours.
TL;DR: A room-temperature perovskite material yielding a power conversion efficiency of 18.1% (stabilized at 17.7%) is demonstrated by judicious selection of cations, showing great potential for low-cost, large-scale manufacturing such as roll-to-roll processing.
Abstract: A room-temperature perovskite material yielding a power conversion efficiency of 18.1% (stabilized at 17.7%) is demonstrated by judicious selection of cations. Both cesium and methylammonium are necessary for room-temperature formamidinium-based perovskite to obtain the photoactive crystalline perovskite phase and high-quality crystals. This room-temperature-made perovskite material shows great potential for low-cost, large-scale manufacturing such as roll-to-roll processing.
TL;DR: In this article, a comprehensive study of a set of essential intermediate phases determining the perovskite morphology is presented, showing a clear correlation between the composition of the intermediate phases, peculiarities of their crystal structure, and the morphology of the final perovsite films.
Abstract: We found for the first time a new origin of selection of perovskite crystallization pathways from DMF solutions containing MAI and PbI2 to present here a comprehensive study of a full set of essential intermediate phases determining the perovskite’s morphology. For all three discovered structurally different intermediate phases forming at a given precursor ratio, we refined their crystal structures by synchrotron X-ray radiation and investigated dynamics and phase assemblage in the course of decomposition. As a result, we revealed a clear correlation between the composition of the intermediate phases, peculiarities of their crystal structure, and the morphology of the final perovskite films. Using the DFT method we calculated formation enthalpies of these intermediate phases and explained the preferential precipitation of DMSO-adduct rather than DMF-adduct in an antisolvent approach. This finding opens up a possibility of design-on-demand of perovskite materials using simple soft chemistry approaches.
TL;DR: This study provides a thorough understanding of the impact of inorganic cations on the properties and performance of highly efficient devices, and also highlights new strategies to fabricate efficient multiple-cation-based PSCs.
Abstract: Perovskite solar cells (PSCs) based on cesium (Cs)- and rubidium (Rb)-containing perovskite films show highly reproducible performance; however, a fundamental understanding of these systems is still emerging. Herein, this study has systematically investigated the role of Cs and Rb cations in complete devices by examining the transport and recombination processes using current–voltage characteristics and impedance spectroscopy in the dark. As the credibility of these measurements depends on the performance of devices, this study has chosen two different PSCs, (MAFACs)Pb(IBr)3 (MA = CH3NH3+, FA = CH(NH2)2+) and (MAFACsRb)Pb(IBr)3, yielding impressive performances of 19.5% and 21.1%, respectively. From detailed studies, this study surmises that the confluence of the low trap-assisted charge-carrier recombination, low resistance offered to holes at the perovskite/2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9-spirobifluorene interface with a low series resistance (Rs), and low capacitance leads to the realization of higher performance when an extra Rb cation is incorporated into the absorber films. This study provides a thorough understanding of the impact of inorganic cations on the properties and performance of highly efficient devices, and also highlights new strategies to fabricate efficient multiple-cation-based PSCs.
TL;DR: Cs+ and Rb+ are shown to be more efficient in the stabilization of the perovskite α phase than MA+.
Abstract: In this work we perform a computational study comparing the influence of monovalent cation substitution by methylammonium (MA+), cesium (Cs+), and rubidium (Rb+) on the properties of formamidinium lead triiodide (FAPbI3)-based perovskites. The relative stability of the desired, photoactive perovskite α phase (“black phase”) and the nonphotoactive, nonperovskite δ phase (“yellow phase”) is studied as a function of dopant nature, concentration and temperature. Cs+ and Rb+ are shown to be more efficient in the stabilization of the perovskite α phase than MA+. Furthermore, varying the dopant concentration allows changing the relative stability at different temperatures, in particular stabilizing the α phase already at 200 K. Upon Cs+ or Rb+ doping, the corresponding onset of the optical spectrum is blue-shifted by 0.1–0.2 eV with respect to pure FAPbI3.