Showing papers on "Perovskite solar cell published in 2017"
TL;DR: The introduction of additional iodide ions into the organic cation solution, which is used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects, enabling the fabrication of PSCs with a certified power conversion efficiency.
Abstract: The formation of a dense and uniform thin layer on the substrates is crucial for the fabrication of high-performance perovskite solar cells (PSCs) containing formamidinium with multiple cations and mixed halide anions. The concentration of defect states, which reduce a cell’s performance by decreasing the open-circuit voltage and short-circuit current density, needs to be as low as possible. We show that the introduction of additional iodide ions into the organic cation solution, which are used to form the perovskite layers through an intramolecular exchanging process, decreases the concentration of deep-level defects. The defect-engineered thin perovskite layers enable the fabrication of PSCs with a certified power conversion efficiency of 22.1% in small cells and 19.7% in 1-square-centimeter cells.
4,603 citations
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: Zhao et al. as mentioned in this paper presented a certified 17% efficient tin and lead perovskite solar cell, which is integrated as the lowbandgap component of a tandem device with 21% efficiency.
Abstract: Tandem solar cells using only metal-halide perovskite sub-cells are an attractive choice for next-generation solar cells. However, the progress in developing efficient all-perovskite tandem solar cells has been hindered by the lack of high-performance low-bandgap perovskite solar cells. Here, we report efficient mixed tin–lead iodide low-bandgap (∼1.25 eV) perovskite solar cells with open-circuit voltages up to 0.85 V and over 70% external quantum efficiencies in the infrared wavelength range of 700–900 nm, delivering a short-circuit current density of over 29 mA cm−2 and demonstrating suitability for bottom-cell applications in all-perovskite tandem solar cells. Our low-bandgap perovskite solar cells achieve a maximum power conversion efficiency of 17.6% and a certified efficiency of 17.01% with a negligible current–voltage hysteresis. When mechanically stacked with a ∼1.58 eV bandgap perovskite top cell, our best all-perovskite 4-terminal tandem solar cell shows a steady-state efficiency of 21.0%. All-perovskite tandem solar cells hold the promise of high efficiencies whilst safeguarding the ease of fabrication intrinsic to perovskites. Here, Zhao et al. present a certified 17% efficient tin and lead perovskite solar cell, which is integrated as the low-bandgap component of a tandem device with 21% efficiency.
590 citations
TL;DR: The UCLA team has successfully passivated perovskite film by controlling the film growth with functional polymers as additive, which opens up a new class of chemical additives for improving perovSkite performance and should pave the way toward improving perOVskite solar cells for high efficiency and stability.
Abstract: The solution processing of polycrystalline perovskite films introduces trap states that can adversely affect their optoelectronic properties. Motivated by the use of small-molecule surfactants to improve the optoelectronic performance of perovskites, we demonstrate the use of polymers with coordinating groups to improve the performance of solution-processed semiconductor films. The use of these polymer modifiers results in a marked change in the electronic properties of the films, as measured by both carrier dynamics and overall device performance. The devices grown with the polymer poly(4-vinylpyridine) (PVP) show significantly enhanced power conversion efficiency from 16.9 ± 0.7% to 18.8 ± 0.8% (champion efficiency, 20.2%) from a reverse scan and stabilized champion efficiency from 17.5 to 19.1% [under a bias of 0.94 V and AM (air mass) 1.5-G, 1-sun illumination over 30 min] compared to controls without any passivation. Treating the perovskite film with PVP enables a VOC of up to 1.16 V, which is among the best reported for a CH3NH3PbI3 perovskite solar cell and one of the lowest voltage deficits reported for any perovskite to date. In addition, perovskite solar cells treated with PVP show a long shelf lifetime of up to 90 days (retaining 85% of the initial efficiency) and increased by a factor of more than 20 compared to those without any polymer (degrading to 85% after ~4 days). Our work opens up a new class of chemical additives for improving perovskite performance and should pave the way toward improving perovskite solar cells for high efficiency and stability.
539 citations
TL;DR: In this paper, a two-step sequential deposition method is developed to grow high-quality Bγ-CsSnI3 thin films and their unique phase change in atmosphere is explored in detail.
352 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: In this article, the impact of Cs dopant on the optoelectronic properties of NiOx and the photovoltaic performance has been investigated in inverted planar perovskite solar cells.
Abstract: Organic–inorganic hybrid perovskite solar cells have resulted in tremendous interest in developing next generation photovoltaics due to high record efficiency exceeding 22%. For inverted structure perovskite solar cells, the hole extraction layers play a significant role in achieving efficient and stable perovskite solar cell by modifying charge extraction, interfacial recombination losses, and band alignment. Here, cesium doped NiOx is selected as a hole extraction layer to study the impact of Cs dopant on the optoelectronic properties of NiOx and the photovoltaic performance. Cs doped NiOx films are prepared by a simple solution-based method. Both doped and undoped NiOx films are smooth and highly transparent, while the Cs doped NiOx exhibits better electron conductivity and higher work function. Therefore, Cs doping results in a significant improvement in the performance of NiOx-based inverted planar perovskite solar cells. The best efficiency of Cs doped NiOx devices is 19.35%, and those devices show high stability as well. The improved efficiency in devices with Cs:NiOx is attributed to a significant improvement in the hole extraction and better band alignment compared to undoped NiOx. This work reveals that Cs doped NiOx is very promising hole extraction material for high and stable inverted perovskite solar cells.
318 citations
TL;DR: In this paper, a mesoscopic perovskite solar cell using CsPb0.98Sr0.02I2Br achieves a stabilized efficiency at 10.8%.
Abstract: Cesium (Cs) metal halide perovskites for photovoltaics have gained research interest due to their better thermal stability compared to their organic–inorganic counterparts. However, demonstration of highly efficient Cs-based perovskite solar cells requires high annealing temperature, which limits their use in multijunction devices. In this work, low-temperature-processed cesium lead (Pb) halide perovskite solar cells are demonstrated. We have also successfully incorporated the less toxic strontium (Sr) at a low concentration that partially substitutes Pb in CsPb1–xSrxI2Br. The crystallinity, morphology, absorption, photoluminescence, and elemental composition of this low-temperature-processed CsPb1–xSrxI2Br are studied. It is found that the surface of the perovskite film is enriched with Sr, providing a passivating effect. At the optimal concentration (x = 0.02), a mesoscopic perovskite solar cell using CsPb0.98Sr0.02I2Br achieves a stabilized efficiency at 10.8%. This work shows the potential of inorgani...
301 citations
TL;DR: It is demonstrated that interfacial chemical interactions are a critical factor in determining the optoelectronic properties of perovskite solar cells, and proper interfacial interactions can significantly reduce trap state density and facilitate the interfacial charge transfer.
Abstract: The ionic nature of perovskite photovoltaic materials makes it easy to form various chemical interactions with different functional groups. Here, we demonstrate that interfacial chemical interactions are a critical factor in determining the optoelectronic properties of perovskite solar cells. By depositing different self-assembled monolayers (SAMs), we introduce different functional groups onto the SnO2 surface to form various chemical interactions with the perovskite layer. It is observed that the perovskite solar cell device performance shows an opposite trend to that of the energy level alignment theory, which shows that chemical interactions are the predominant factor governing the interfacial optoelectronic properties. Further analysis verifies that proper interfacial interactions can significantly reduce trap state density and facilitate the interfacial charge transfer. Through use of the 4-pyridinecarboxylic acid SAM, the resulting perovskite solar cell exhibits striking improvements to the reach t...
275 citations
TL;DR: In this paper, the authors highlight the important theoretical results reported in literature for the understanding of the unique structural, electronic, optical, and defect properties of lead halide perovskite materials.
Abstract: Lead halide perovskites have recently emerged as promising absorbers for fabricating low-cost and high-efficiency thin-film solar cells. The record power conversion efficiency of lead halide perovskite-based solar cells has rapidly increased from 3.8% in 2009 to 22.1% in early 2016. Such rapid improvement is attributed to the superior and unique photovoltaic properties of lead halide perovskites, such as the extremely high optical absorption coefficients and super-long photogenerated carrier lifetimes and diffusion lengths that are not seen in any other polycrystalline thin-film solar cell materials. In the past a few years, theoretical approaches have been extensively applied to understand the fundamental mechanisms responsible for the superior photovoltaic properties of lead halide perovskites and have gained significant insights. This review article highlights the important theoretical results reported in literature for the understanding of the unique structural, electronic, optical, and defect properties of lead halide perovskite materials. For comparison, we also review the theoretical results reported in literature for some lead-free perovskites, double perovskites, and nonperovskites.
260 citations
TL;DR: An ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovSKite-based photovoltaics.
Abstract: Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X·NH4PbX3(H2O)2 (X=I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovskite-based photovoltaics.
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: It is demonstrated that the effect of light-enhanced ion migration in CH3NH3PbI3 can be eliminated by inorganic Cs substitution, leading to an ultrastable perovskite solar cell.
Abstract: Due to light-induced effects in CH3NH3-based perovskites, such as ion migration, defects formation, and halide segregation, the degradation of CH3NH3-based perovskite solar cells under maximum power point is generally implicated. Here we demonstrated that the effect of light-enhanced ion migration in CH3NH3PbI3 can be eliminated by inorganic Cs substitution, leading to an ultrastable perovskite solar cell. Quantitatively, the ion migration barrier for CH3NH3PbI3 is 0.62 eV under dark conditions, larger than that of CsPbI2Br (0.45 eV); however, it reduces to 0.07 eV for CH3NH3PbI3 under illumination, smaller than that for CsPbI2Br (0.43 eV). Meanwhile, photoinduced halide segregation is also suppressed in Cs-based perovskites. Cs-based perovskite solar cells retained >99% of the initial efficiency (10.3%) after 1500 h of maximum power point tracking under AM1.5G illumination, while CH3NH3PbI3 solar cells degraded severely after 50 h of operation. Our work reveals an uncovered mechanism for stability improv...
TL;DR: In this paper, the progress of perovskite solar cells with a particular emphasis on fabrication processes and instrumentation that have scale-up potential is reviewed, focusing on lifetime measurement and quantification protocols for commercialization.
TL;DR: In this paper, a comprehensive first-principles investigation into surface defects of tetragonal CH3NH3PbI3 was conducted, and it was proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice.
Abstract: The trapping of charge carriers at defects on surfaces or grain boundaries is detrimental for the performance of perovskite solar cells (PSCs). For example, it is the main limiting factor for carrier lifetime. Moreover, it causes hysteresis in the current–voltage curves, which is considered to be a serious issue for PSCs’ operation. In this work, types of surface defects responsible for carrier trapping are clarified by a comprehensive first-principles investigation into surface defects of tetragonal CH3NH3PbI3 (MAPbI3). Considering defect formation energetics, it is proposed that a Pb-rich condition is preferred to an I-rich one; however, a moderate condition might possibly be the best choice. Our result paves the way for improving the performance of PSCs through a rational strategy of suppressing carrier trapping at surface defects.
TL;DR: This work provides a simple and effective method to enhance the efficiency of the 2D perovskite solar cell and performs unique stability with almost unchanged PCE during the period of storage in purified N2 glove box.
Abstract: Vertically oriented highly crystalline 2D layered (BA)2 (MA)n-1 Pbn I3n+1 (BA = CH3 (CH2 )3 NH3 , MA = CH3 NH3 , n = 3, 4) perovskite thin-films are fabricated with the aid of ammonium thiocyanate (NH4 SCN) additive through one-step spin-coating process. The humidity-stability of the film is certified by the almost unchanged X-ray diffraction patterns after exposed to humid atmosphere (Hr = 55 ± 5%) for 40 d. The photovoltaic devices with the structure of indium tin oxide(ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate)/(BA)2 (MA)n-1 Pbn I3n+1 (n = 3,4)/[6,6]-phenyl-C61 -butyric acid methyl ester/Bathocuproine/Ag are fabricated. The devices based on (BA)2 (MA)2 Pb3 I10 perovskite (n = 3) with the precursor composition of BAI:methylammonium iodide:PbI2 :NH4 SCN = 2:2:3:1 (by molar ratio) show an averaged power conversion efficiency (PCE) of 6.82%. In the case of (BA)2 (MA)3 Pb4 I13 (n = 4), a higher PCE of 8.79% is achieved. Both of the unsealed devices perform unique stability with almost unchanged PCE during the period of storage in purified N2 glove box. This work provides a simple and effective method to enhance the efficiency of the 2D perovskite solar cell.
TL;DR: In this paper, an ultra-thin ALD Al2O3 film was used to conformally deposit the material on top of the perovskite absorber to provide a tunnel contact.
Abstract: Perovskite materials are drawing tremendous interest for photovoltaic solar cell applications, but are hampered by intrinsic material and device instability issues. Such issues can arise from environmental influences as well as from the chemical incompatibility of the perovskite layer with charge transport layers and electrodes used in the device stack. Several attempts have been made to address the instability issue, mostly concentrating on the substitution of the organic cations in the perovskite lattice, and on alternatives for the organic charge extraction layers, without laying much emphasis on stabilising the existing, conventional high efficiency methylammonium lead iodide/spiro-OMeTAD based devices. To address the latter issue, we utilized atomic layer deposition (ALD) as a straightforward and soft deposition process to conformally deposit Al2O3 on top of the perovskite absorber. An ultra-thin ALD Al2O3 film effectively protects the perovskite layer while it is sufficiently thin enough to provide a tunnel contact. The fabricated perovskite solar cells (PSCs) exhibit superior device performance with a stabilised power conversion efficiency (PCE) of 18%, a significant reduction in hysteresis loss, and enhanced long-term stability (beyond 60 days) as a function of the unencapsulated storage time in ambient air, under humidity conditions ranging from 40 to 70% at room temperature. PCE measurements after 70 days of humidity exposure show that the devices incorporating 10 cycles of ALD Al2O3 could significantly retard the humidity-induced degradation thereby retaining about 60–70% of its initial PCE, while that of the reference devices drops to a remaining 12% of their initial PCE. This work successfully addresses and tackles the problem of the hybrid organic–inorganic IV-halide perovskite solar cell’s instability in a humid environment, and the key findings pave the way to the upscaling of these devices.
TL;DR: The power-conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased rapidly from about 4% to 22% during the past few years as mentioned in this paper.
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: In this paper, CsPbCl3:Mn-based quantum dots (QDs) are synthesized and applied onto the front side of the perovskite solar cells as the energy-downshift (EDS) layer.
Abstract: Parasitic absorption by window layer, electrode layer, and interface layer in the near ultraviolet (UV) region is no longer negligible for high-efficiency perovskite solar cells On the other hand, UV-induced degradation is also a big component of cell instability Herein, CsPbCl3:Mn-based quantum dots (QDs) are synthesized and applied onto the front side of the perovskite solar cells as the energy-down-shift (EDS) layer It is found that with very high quantum yield (∼60%) and larger Stokes shift (>200 nm), the CsPbCl3:Mn QDs effectively convert the normally wasted energy in the UV region (300–400 nm) into usable visible light at ∼590 nm for enhanced power conversion efficiency (PCE) Meanwhile, conversion of the UV rays eliminated a significant loss mechanism that deteriorates perovskite stability As a result, external quantum efficiency in the UV region is significantly increased, leading to an increased short-circuit current (377%) and PCE (334%) Furthermore, the stability of perovskite solar cell
TL;DR: In this article, a two-electrode solar water splitting device combining a Na0.08Ni0.9Fe0.1O2 OER catalyst with a NiP hydrogen evolution reaction catalyst delivers a solar-to-hydrogen conversion efficiency of 11.22%.
Abstract: Transition metal Ni- and Co-based oxides are potential candidates to replace expensive and scarce noble metal-based oxygen evolution reaction (OER) catalysts such as IrO2 and RuO2, which are required for efficient hydrogen production from solar water splitting and rechargeable energy storage technologies. So far, layered NiFe double hydroxide represents the best OER activity among all Ni- and Co-based oxides. Here, we report new layered Na1−xNiyFe1−yO2 double oxide OER catalysts exhibiting activity and stability surpassing those of noble metal OER catalysts including IrO2 and RuO2, and a layered NiFe double hydroxide OER catalyst. The superior catalytic properties can be ascribed to the layered structure as well as the enhanced covalency of Ni and Fe. Powered by a lead halide perovskite solar cell with a power conversion efficiency of 14.69%, a two-electrode solar water-splitting device combining a Na0.08Ni0.9Fe0.1O2 OER catalyst with a NiP hydrogen evolution reaction catalyst delivers a solar-to-hydrogen conversion efficiency of 11.22%. Our design and fabrication strategies offer insights for developing highly active electrocatalysts for water splitting and metal–air batteries.
TL;DR: In this review, the advances in the preparation of semitransparent Oscs, DSCs, and PSCs are summarized, focusing on the top transparent electrode materials and device designs, which are all crucial to the performance of these devices.
Abstract: Semitransparent solar cells can provide not only efficient power-generation but also appealing images and show promising applications in building integrated photovoltaics, wearable electronics, photovoltaic vehicles and so forth in the future. Such devices have been successfully realized by incorporating transparent electrodes in new generation low-cost solar cells, including organic solar cells (OSCs), dye-sensitized solar cells (DSCs) and organometal halide perovskite solar cells (PSCs). In this review, the advances in the preparation of semitransparent OSCs, DSCs, and PSCs are summarized, focusing on the top transparent electrode materials and device designs, which are all crucial to the performance of these devices. Techniques for optimizing the efficiency, color and transparency of the devices are addressed in detail. Finally, a summary of the research field and an outlook into the future development in this area are provided.
TL;DR: In this article, the mesoporous TiO2 (mTiO2) layer with graphene flakes was used to tune the interface properties of perovskite solar cell (PSC) layer components.
Abstract: Interfaces between perovskite solar cell (PSC) layer components play a pivotal role in obtaining high-performance premium cells and large-area modules. Graphene and related two-dimensional materials (GRMs) can be used to “on-demand” tune the interface properties of PSCs. We successfully used GRMs to realize large-area (active area 50.6 cm2) perovskite-based solar modules (PSMs), achieving a record high power conversion efficiency of 12.6%. We on-demand modulated the photoelectrode charge dynamic by doping the mesoporous TiO2 (mTiO2) layer with graphene flakes. Moreover, we exploited lithium-neutralized graphene oxide flakes as interlayer at the mTiO2/perovskite interface to improve charge injection. Notably, prolonged aging tests have shown the long-term stability for both small- and large-area devices using graphene-doped mTiO2. Furthermore, the possibility of producing and processing GRMs in the form of inks opens a promising route for further scale-up and stabilization of the PSM, the gateway for the c...
TL;DR: This work has found that (μ + t)η, where μ and η are the octahedral factor and the atomic packing fraction, respectively, demonstrates a remarkably linear correlation with thermodynamic stability and may help the efficient high-throughput search for emerging stable perovskites and precise control of chemical compositions for stabilizing current perovkites.
Abstract: Stability is of central importance in current perovskite solar cell research and applications. Goldschmidt tolerance factor (t) recently provided qualitative guidance for experimentalists to engineer stable ABX3 perovskite by tuning effective ionic size with mixing cations or anions and for theorists to search emerging perovskites. Through first-principles calculations, we have calculated decomposition energies of 138 perovskite compounds of potential solar cell applications. Instead of t, we have found that (μ + t)η, where μ and η are the octahedral factor and the atomic packing fraction, respectively, demonstrates a remarkably linear correlation with thermodynamic stability. As a stability descriptor, (μ + t)η is able to predict the relative stability among any two perovskites with an accuracy of ∼90%. This trend is then used to predict decomposition energies of another 69 perovskites, and the results are in excellent agreement with first-principles calculations, indicating the generalization of the tre...
TL;DR: Nb-doped TiO2 films are prepared by a facile one-port chemical bath process at low temperature and applied as a high quality ETL for planar PSCs and are more efficient for photogenerated electron injection and extraction.
Abstract: The conduction band energy, conductivity, mobility, and electronic trap states of electron transport layer (ETL) are very important to the efficiency and stability of a planar perovskite solar cell (PSC). However, as the most widely used ETL, TiO2 often needs to be prepared under high temperature and has unfavorable electrical properties such as low conductivity and high electronic trap states. Modifications such as elemental doping are effective methods for improving the electrical properties of TiO2 and the performance of PSCs. In this study, Nb-doped TiO2 films are prepared by a facile one-port chemical bath process at low temperature (70 °C) and applied as a high quality ETL for planar PSCs. Compared with pure TiO2, the Nb-doped TiO2 is more efficient for photogenerated electron injection and extraction, showing higher conductivity, higher mobility, and lower trap-state density. A PSC with 1% Nb-doped TiO2 yielded a power conversion efficiency of more than 19%, with about 90% of its initial efficiency...
TL;DR: In this article, the authors show that the cooperation of lead thiocyanate additive and a solvent annealing process can effectively increase the grain size of mixed-cation lead mixed-halide perovskite thin films while avoiding excess lead iodide formation.
Abstract: We show that the cooperation of lead thiocyanate additive and a solvent annealing process can effectively increase the grain size of mixed-cation lead mixed-halide perovskite thin films while avoiding excess lead iodide formation. As a result, the average grain size of the wide-bandgap mixed-cation lead perovskite thin films increases from 66 ± 24 to 1036 ± 111 nm, and the mean carrier lifetime shows a more than 3-fold increase, from 330 ns to over 1000 ns. Consequently, the average open-circuit voltage of wide-bandgap perovskite solar cells increases by 80 (70) mV, and the average power conversion efficiency (PCE) increases from 13.44 ± 0.48 (11.75 ± 0.34) to 17.68 ± 0.36 (15.58 ± 0.55)% when measured under reverse (forward) voltage scans. The best-performing wide-bandgap perovskite solar cell, with a bandgap of 1.75 eV, achieves a stabilized PCE of 17.18%.
TL;DR: The type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures and Grain-boundary engineering is included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time.
Abstract: Perovskite solar cells (PCSs) are composed of organic-inorganic lead halide perovskite as the light harvester. Since the first report on a long-term-durable, 9.7 % efficient, solid-state perovskite solar cell, organic-inorganic halide perovskites have received considerable attention because of their excellent optoelectronic properties. As a result, a power conversion efficiency (PCE) exceeding 22 % was certified. Controlling the grain size, grain boundary, morphology, and defects of the perovskite layer is important for achieving high efficiency. In addition, interfacial engineering is equally or more important to further improve the PCE through better charge collection and a reduction in charge recombination. In this Review, the type of interfacial layers and their impact on photovoltaic performance are investigated for both the normal and the inverted cell architectures. Four different interfaces of fluorine-doped tin oxide (FTO)/electron-transport layer (ETL), ETL/perovskite, perovskite/hole-transport layer (HTL), and HTL/metal are classified, and their roles are investigated. The effects of interfacial engineering with organic or inorganic materials on photovoltaic performance are described in detail. Grain-boundary engineering is also included because it is related to interfacial engineering and the grain boundary in the perovskite layer plays an important role in charge conduction, recombination, and chargecarrier life time.
TL;DR: An ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO 2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties and exhibits a remarkable improvement of all J–V parameters.
Abstract: Reducing the energy loss and retarding the carrier recombination at the interface are crucial to improve the performance of the perovskite solar cell (PSCs). However, little is known about the recombination mechanism at the interface of anode and SnO2 electron transfer layer (ETL). In this work, an ultrathin wide bandgap dielectric MgO nanolayer is incorporated between SnO2:F (FTO) electrode and SnO2 ETL of planar PSCs, realizing enhanced electron transporting and hole blocking properties. With the use of this electrode modifier, a power conversion efficiency of 18.23% is demonstrated, an 11% increment compared with that without MgO modifier. These improvements are attributed to the better properties of MgO-modified FTO/SnO2 as compared to FTO/SnO2, such as smoother surface, less FTO surface defects due to MgO passivation, and suppressed electron-hole recombinations. Also, MgO nanolayer with lower valance band minimum level played a better role in hole blocking. When FTO is replaced with Sn-doped In2O3 (ITO), a higher power conversion efficiency of 18.82% is demonstrated. As a result, the device with the MgO hole-blocking layer exhibits a remarkable improvement of all J-V parameters. This work presents a new direction to improve the performance of the PSCs based on SnO2 ETL by transparent conductive electrode surface modification.
TL;DR: In this article, a solution-processed polymer layer between the perovskite layer and the hole-transporting layer was added to improve the performance of perov-skite solar cells.
Abstract: Solution-processed organo-lead halide perovskite solar cells with deep pinholes in the perovskite layer lead to shunt-current leakage in devices. Herein, we report a facile method for improving the performance of perovskite solar cells by inserting a solution-processed polymer layer between the perovskite layer and the hole-transporting layer. The photovoltaic conversion efficiency of the perovskite solar cell increased to 18.1% and the stability decreased by only about 5% during 20 days of exposure in moisture ambient conditions through the incorporation of a poly(methyl methacrylate) (PMMA) polymer layer. The improved photovoltaic performance of devices with a PMMA layer is attributed to the reduction of carrier recombination loss from pinholes, boundaries, and surface states of perovskite layer. The significant gain generated by this simple procedure supports the use of this strategy in further applications of thin-film optoelectronic devices.
TL;DR: In this paper, the authors showed that the unsuitably small ionic radius of Rb+ can lead to several nonphotoactive side-products, such as RbPb2I4Br.
Abstract: Rubidium and cesium cations have been recently identified as enhancers for perovskite solar cell performance. However, the impact of these inorganic cations on the stability of the (FA0.83MA0.17)Pb(I0.83Br0.17)3 perovskite crystal lattice has not been fully understood yet. Here, we show via in situ X-ray diffraction and energy-dispersive X-ray spectrometry measurements that the unsuitably small ionic radius of Rb+ can lead to several nonphotoactive side-products. During the perovskite film synthesis, RbPb(I1–xBrx)3 is formed, while exposure to humid air leads to the rapid formation of another hitherto unreported side phase (RbPb2I4Br). The formation of the Rb-rich side phases not only results in a loss of light absorption but also extracts bromide ions from the photoactive perovskite phase, thereby reducing its band gap. In comparison, the moisture-assisted formation of a CsPb2I4Br phase upon Cs-addition occurs on a significantly longer time scale than its Rb analog. While the incorporation of Cs+ remains...