JIALINGBO

A systematic summary of the use of fluorinated compounds in each layer of perovskite solar cells is reviewed. Fluorinated compounds induce better electron and hole transporting material quality. The high electronegativity of the fluorine element allows an efficient charge‐extraction and transport at the perovskite surface and interfaces. More importantly, these fluorinated compounds greatly enhance both device efficiency and long‐term stability.

Abstract

Several valuable scientific investigations have been conducted these last few years in materials design and device engineering for perovskite solar cells (PSCs) to make them competitive compared to traditional silicon‐based photovoltaic technologies. Consequently, high power conversion efficiency beyond 25% is nowadays reported. However, their long‐term stability remains a significant challenge to overcome. Herein, the influence of fluorinated compounds on each layer of PSCs devices and their impact on the resulted device performances and stability is spotlighted. The fluorinated compounds exhibit attractive properties due to their very high electronegativity attributed to the fluorine atom, and their strong hydrophobicity. Thus, the introduction of these compounds is found to be a successful strategy to positively suppress the surface trap states, enhancing charge collection and reducing interfacial charge recombination. Besides, a better film quality and better energy level alignment is obtained, resulting in the improvement of device photovoltaic parameters such as the open‐circuit voltage (V _oc), short‐circuit current (J _sc), and fill factor (FF), and then, the device's overall power conversion efficiency (PCE). Their long‐term stability is also found to further be improved.

High efficiency and humidity‐resistant flexible perovskite solar cells (FPSCs) are fabricated, using a SnO₂/Al(acac)₃ bilayer as the electron transfer layer. FPSCs present long‐time stability in ambient conditions (>50% relative humidity) without encapsulation, while yielding a power conversion efficiency (PCE) of up to 20.87%. That may open a new way to improve the stability of FPSCs.

Flexible perovskite solar cells (FPSCs) with high efficiency and excellent mechanical flexible properties have attracted enormous interest as a promising photovoltaic technology in recent years. However, the performance or stability of FPSCs is still far inferior to that of conventional glass‐based perovskite solar cells (PSCs). Herein, a cross‐linking agent called aluminum acetylacetonate (Al(acac)₃) is introduced as an interface layer between electron transport layer and perovskite absorber. Due to the well‐matched energy levels and improved grain size and crystallinity of the perovskite, a champion device with the highest power conversion efficiency (PCE) of 20.87% is achieved on the FPSCs. The device retains about 80% of its initial performance after 1000 h under >50% relative humidity without encapsulation. In addition, attributed to the Al(acac)₃ super bending resistance, more than 91% of the original PCE is retained after 1500 bending cycles. This work proposes the substrate side optimization for improving device efficiency and stability which may provide a novel concept for promoting the development of FPSCs.

The solvent engineering of precursor solutions toward efficient perovskite solar cells (PSCs) is reviewed comprehensively. The key role of solvent engineering for solution‐processed perovskite film is highlighted, especially for the large‐area production of PSCs. Light is shed on the significance of solvent engineering in PSCs, and critical guidance for future commercialization development of highly efficient PSCs is provided.

Abstract

Solar cells based on emerging organic–inorganic hybrid perovskite materials have reached certified power conversion efficiency as high as 25.5%, showing great potential in the next generation of photovoltaics toward large‐scale industrialization. The most competitive feature of perovskite solar cells (PSCs) is that the perovskite light absorber can be fabricated by a low‐cost solution method. For the solution method, the characteristics of the solvent play a key role in determining the crystallization kinetics, growth orientation, and optoelectronic properties of the perovskite film. Although significant progress has been made in the field of solvent engineering in PSCs, it is still challenging for the solution method to sustainably produce industrial‐scale PSCs for future commercialization applications. Herein, the advanced progress of solvent engineering of precursor solution in terms of coordination regulation and toxicity reduction is highlighted. The physical and chemical characteristics of different solvents in reducing the toxicity of the solvent system, regulating the coordination property of the precursor solution, controlling the film‐forming process of the perovskite film, and adjusting the photovoltaic performance of the PSC are systematically discussed. Lastly, important perspectives on solvent engineering of the perovskite precursor solution toward future industrial production of high‐performance PSCs are provided.

Ravishankar et al. claimed that drive-level capacitance profiling (DLCP) cannot resolve trap density in perovskites of given thickness. We point out that the trap densities derived by DLCP are from the differential capacitance at different frequencies; thus, the background charges caused by diffusion and geometry capacitance have been subtracted. Even for the nondifferential doping analysis, the contribution from diffusion capacitance is negligible and that from geometry capacitance is excluded.

To enable highly efficient and stable CsFA perovskite solar cells, a joint experimental–computational study is conducted. It is shown that by treating the perovskite with an n‐type molecular dopant, the band bending is increased, shaping the electric field across the active layer to overcome limited diffusive transport. Using this strategy, CsFA solar cell devices are fabricated with stabilized power conversion efficiencies of 20.3%.

Abstract

Perovskites with the multi‐cation composition of cesium (Cs), methylammonium (MA), and formamidinium (FA) (CsMAFA) are pursued for their high power conversion efficiencies, but they are limited by their thermal stability. To withstand damp‐heat accelerated aging MA‐free compositions such as CsFA are of interest, but these exhibit lower carrier diffusion lengths and thus lesser performance in photovoltaic devices. A band engineering strategy that overcomes limited carrier diffusion within inverted perovskite solar cells based on CsFA is reported. A joint experimental‐computational study shows that treating the perovskite with an n‐type molecular dopant increases band bending, shaping the electric field across the active layer to overcome limited diffusive transport. Using this strategy, CsFA solar cell devices with stabilized power conversion efficiencies of 20.3%, a high value for devices using CsFA active layers, are fabricated.

N,1‐fluoroformamidinium iodide (F‐FAI), whose cation replaces one amino group of guanidinium (GA⁺) with electron‐withdrawing fluorine group, is synthesized and used as an additive for printable triple mesoscopic perovskite solar cells. The electron‐withdrawing effect of fluorine promotes the molecular polarity of F‐FA, which enhances the interaction of F‐FA⁺ with MAPbI₃ than that of GA⁺. Compared with guanidinium iodide, improved performance is achieved with the addition of F‐FAI.

Abstract

Additives are widely adopted for efficient perovskite solar cells (PSCs), and proper additive design contributes a lot to PSCs’ various breakthroughs. Herein, a novel additive of N,1‐fluoroformamidinium iodide (F‐FAI), whose cation replaces one amino group in guanidinium (GA⁺) with electron‐withdrawing fluorine group, is synthesized and applied as the additive for PSCs. The electron‐withdrawing effect of fluorine promotes the molecular polarity of N,1‐fluoroformamidine (F‐FA), enhancing the interaction of N,1‐fluoroformamidinium (F‐FA⁺) with MAPbI₃. Compared with the nonpolar GA⁺, F‐FA⁺ improves the crystallinity, passivates the defect, and downshifts the Fermi level of MAPbI₃ more significantly. The charge transfer and built‐in field in printable triple mesoscopic PSCs are therefore enhanced. Moreover, charge transport in MAPbI₃ is also promoted by F‐FAI. With these benefits, a power conversion efficiency of 17.01% for printable triple mesoscopic PSCs with improved open‐circuit voltage and fill factor is obtained with the addition of F‐FAI, superior to the efficiency of 15.24% for those devices with guanidinium iodide additives.

A charge‐transfer complex strategy to reduce the energy disorder of organic semiconductor (OS) charge transport layers (CTLs) by doping a well‐designed OS (BDT‐Si) with electron‐acceptor features in a commercial hole‐transport material (PTAA) is proposed. As a result, the p–i–n planar perovskite solar cells with the optimized hole‐transport layer exhibit the best power conversion efficiency of 21.87%, and good operating stability at maximum power point under continuous illumination.

Abstract

Solution‐processed organic semiconductor charge‐transport layers (OS‐CTLs) with high mobility, low trap density, and energy level alignment have dominated the important progress in p–i–n planar perovskite solar cells (pero‐SCs). Unfortunately, their inevitable long chains result in weak molecular stacking, which is likely to generate high energy disorder and deteriorate the charge‐transport ability of OS‐CTLs. Here, a charge‐transfer complex (CTC) strategy to reduce the energy disorder in the OS‐CTLs by doping an organic semiconductor, 4,4′‐(4,8‐bis(5‐(trimethylsilyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl)bis(N,N‐bis(4‐methoxyphenyl)aniline) (BDT‐Si), in a commercial hole‐transport layer (HTL), poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl)amine (PTAA), is proposed. The formation of the CTC makes the PTAA conjugated backbone electron‐deficient, resulting in a quinoidal and stiffer character, which is likely to planarize the PTAA backbone and enhance the ordering of the film in nanoscale. The resultant HTL exhibits a reduced energy disorder, which simultaneously promotes hole transport in the HTL, hole extraction at the interface, energy level alignment, and quasi‐Fermi level splitting in the device. As a result, the p–i–n planar pero‐SCs with optimized HTL exhibit the best power conversion efficiency of 21.87% with good operating stability. This finding demonstrates that the CTC strategy is an effective way to reduce the energy disorder in HTLs and to improve the performance of planar pero‐SCs.

The strong interaction between F and Sn changes the electron cloud density around Sn atoms by introducing RbF into SnO₂ colloidal dispersion, contributing to the improved electron mobility of SnO₂. While spin‐coating RbF onto the SnO₂ surface, the Rb⁺ cations escape into the bulk perovskite, which inhibits ion migration and decreases the trap density.

Abstract

Regulating the electron transport layer (ETL) has been an effective way to promote the power conversion efficiency (PCE) of perovskite solar cells (PSCs) as well as suppress their hysteresis. Herein, the SnO₂ ETL using a cost‐effective modification material rubidium fluoride (RbF) is modified in two methods: 1) adding RbF into SnO₂ colloidal dispersion, F and Sn have a strong interaction, confirmed via X‐ray photoelectron spectra and density functional theory results, contributing to the improved electron mobility of SnO₂; 2) depositing RbF at the SnO₂/perovskite interface, Rb⁺ cations actively escape into the interstitial sites of the perovskite lattice to inhibit ions migration and reduce non‐radiative recombination, which dedicates to the improved open‐circuit voltage (V _oc) for the PSCs with suppressed hysteresis. In addition, double‐sided passivated PSCs, RbF on the SnO₂ surface, and p‐methoxyphenethylammonium iodide on the perovskite surface, produces an outstanding PCE of 23.38% with a V _oc of 1.213 V, corresponding to an extremely small V _oc deficit of 0.347 V.

A thermally stable perovskite solar cell is developed by capturing mobile lithium ions using a new molecular hole transporter, 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl)amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38), where a strong interaction of the lithium ions in lithium bis(trifluoromethanesulfonyl)imide with the 5‐octylthieno[3,4‐c]pyrrole‐4,6‐dione (octyl‐TPD) moiety in HL38 is responsible for maintaining ≈86% of the initial power conversion efficiency for over 1000 h at 85 °C.

Abstract

A thermally stable perovskite solar cell (PSC) based on a new molecular hole transporter (MHT) of 1,3‐bis(5‐(4‐(bis(4‐methoxyphenyl) amino)phenyl)thieno[3,2‐b]thiophen‐2‐yl)‐5‐octyl‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (coded HL38) is reported. Hole mobility of 1.36 × 10⁻³ cm² V⁻¹ s⁻¹ and glass transition temperature of 92.2 °C are determined for the HL38 doped with lithium bis(trifluoromethanesulfonyl)imide and 4‐tert‐butylpyridine as additives. Interface engineering with 2‐(2‐aminoethyl)thiophene hydroiodide (2‐TEAI) between the perovskite and the HL38 improves the power conversion efficiency (PCE) from 19.60% (untreated) to 21.98%, and this champion PCE is even higher than that of the additive‐containing 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (spiro‐MeOTAD)‐based device (21.15%). Thermal stability testing at 85 °C for over 1000 h shows that the HL38‐based PSC retains 85.9% of the initial PCE, while the spiro‐MeOTAD‐based PSC degrades unrecoverably from 21.1% to 5.8%. Time‐of‐flight secondary‐ion mass spectrometry studies combined with Fourier transform infrared spectroscopy reveal that HL38 shows lower lithium ion diffusivity than spiro‐MeOTAD due to a strong complexation of the Li⁺ with HL38, which is responsible for the higher degree of thermal stability. This work delivers an important message that capturing mobile Li⁺ in a hole‐transporting layer is critical in designing novel MHTs for improving the thermal stability of PSCs. In addition, it also highlights the impact of interface design on non‐conventional MHTs.

Highly efficient CsPbI_1.5Br_1.5 perovskite solar cells (PSCs) are achieved via introducing fluorescein isothiocyanate (FITC) organic dye as passivator. FITC not only reduces the metal ion related trap states but also improves film crystallinity, resulting in an enhancement of device efficiency from 12.3% to 14.05%. In addition, it is demonstrated that CsPbI_1.5Br_1.5 perovskite shows the optimal halide composition for inorganic PSCs.

Abstract

All‐inorganic perovskite solar cells (PSCs) have recently received growing attention as a promising template to solve the thermal instability of organic–inorganic PSCs. However, the thermodynamic phase instability and relatively low device efficiency pose challenges. Herein, highly efficient and stable CsPbI_1.5Br_1.5 compositional perovskite‐based inorganic PSCs are fabricated using an organic dye, fluorescein isothiocyanate (FITC), as a passivator. The carboxyl and thiocyanate groups of FITC not only minimize the trap states by forming interactions with the under‐coordinated Pb²⁺ ions but also significantly increase the grain size and improve the crystallinity of the perovskite films during annealing. Consequently, perovskite films with superior optoelectronic properties, prolonged carrier lifetime, reduced trap density, and improved stability are obtained. The resulting device yields a champion efficiency of 14.05% with negligible hysteresis, which presents the highest reported efficiency for inorganic CsPbI_1.5Br_1.5 solar cells reported thus far. In addition, FITC can be generally adopted as attractive passivator to improve the performance of CsPbI₂Br‐ and CsPbIBr₂‐based PSCs. Furthermore, with a comprehensive comparison of mixed‐halide inorganic perovskites, it is demonstrated that CsPbI_1.5Br_1.5 compositional perovskite is a promising candidate with the optimal halide composition for high‐performance inorganic PSCs.

The carbon‐based hole‐transporting material (HTM)‐free CsPbBr₃ perovskite solar cell (PSC) achieves a maximized power conversion efficiency (PCE) of 9.82% with an excellent thermal and moisture stability through perovskite film management and multiple‐ionic defect passivation by the introduction of a tetra‐bisphenol A (TBBPA) additive.

High‐quality perovskite films with low imperfections, high hole mobility, and matching energy levels play a crucial role in enhancing performance of perovskite solar cells (PSCs) without hole‐transporting materials (HTMs). Herein, it is demonstrated that the incorporation of a stable tetra‐bisphenol A (TBBPA) with diphenyl ring, polybromides, and hydroxyl groups additive into a perovskite film can simultaneously manipulate the crystal growth and passivate the defects through coordination interaction between the functional group (OH, Br) and the unsaturated halogen and metal ions (Br⁻, Cs⁺, and Pb²⁺), resulting in a reduced grain boundary as well as imperfection and increased hole mobility of the CsPbBr₃ perovskite film. In addition, the valence band of a perovskite film with TBBPA additive is shifted upward to approach the work function of the carbon electrode, thereby improving the energy level alignment. Consequently, a significantly boosted charge extraction and reduced charge recombination of the carbon‐based HTM‐free CsPbBr₃ PSCs is obtained after incorporating the TBBPA additive, yielding a maximum power conversion efficiency of up to 9.82% of the optimized device. Furthermore, the champion PSC without encapsulation displays a remarkable thermal and moisture stability after being kept in ambient air for 720 h at 85 °C and 85% relative humidity, respectively.

This Review describes approaches to improve the performance of PEDOT:PSS/Si hybrid solar cells. The main strategies include modifying PEDOT:PSS, optimizing the light‐trapping effect, passivating the silicon surface, inserting an interface layer, and improving the back contact and the transparent conductive electrode.

Abstract

The emerging energy crisis has focused significant worldwide attention on solar cells. Although crystalline silicon solar cells are currently widely used, their high cost limits the development of solar power generation. Consequently, hybrid solar cells are becoming increasingly important, especially organic‐Si hybrid solar cells (HSCs). Organic‐Si HSCs combine a mature technology and high efficiency with the low‐temperature manufacturing process and tunable optoelectronic properties of organic solar cells. The organic material can be P3HT, carbon nanotubes, graphene, and PEDOT:PSS. Here we review the performance of PEDOT:PSS/Si HSCs and methods for improving their efficiency, such as PEDOT:PSS modification, optimization of the trapping effect, passivation of the silicon surface, addition of an interface layer, improvement of a back contact, and optimization of the metal top electrode. This Review should help fill the gap in this area and provide perspectives for the future development of the PEDOT:PSS/Si HSCs.

Publication date: 15 June 2021

Source: Chemical Engineering Journal, Volume 414

Author(s): Cong Geng, Peng Wei, Huamei Chen, Haichao Liu, Shenshen Zheng, Haobin Wang, Yahong Xie

A multidentate ligand synthetic strategy based on a linear amphiphilic PMMA‐b‐PAA diblock copolymer prepared from RAFT polymerization enables the synthesis of PMMA‐tethered CsPbBr₃/TiO₂ core/shell nanosheets (NSs). These NSs have markedly enhanced stabilities (i.e., thermal, photostability, moisture, polar solvent, aliphatic amine, etc.), and thus potential applications in optoelectronic materials and devices.

Abstract

Approaches to achieve stable perovskite nanocrystals (PNCs) of interest, in particular those with large structural anisotropy, through protective coating of the inorganic shell at a single‐nanocrystal (NC) level are comparatively few and limited in scope. Reported here is a robust amphiphilic‐diblock‐copolymer‐enabled strategy for crafting highly‐stable anisotropic CsPbBr₃ nanosheets (NSs) by in situ formation of a uniform inorganic shell (1st shielding) that is intimately ligated with hydrophobic polymers (2nd shielding). The dual‐protected NSs display an array of remarkable stabilities (i.e., thermal, photostability, moisture, polar solvent, aliphatic amine, etc.) and find application in white‐light‐emitting diodes. In principle, by anchoring other multidentate amphiphilic polymer ligands on the surface of PNCs, followed by templated‐growth of shell materials of interest, a rich variety of dual‐shelled, multifunctional PNCs with markedly improved stabilities can be created for use in optics, optoelectronics, and sensory devices.

The effect of phenethylammonium iodide (PEAI) deposition is investigated for indoor perovskite solar cells (PSCs). With an optimized amount of PEAI, homogenous extraction of photo‐generated carriers is observed. In addition, work function shifts toward the valence band of the surface. This results in enhanced hole collection between the hole transport layer and perovskite interfaces leading to improved performance of indoor PSCs.

Abstract

Halide perovskite‐based photovoltaic (PV) devices have recently emerged for low energy consumption electronic devices such as Internet of Things (IoT). In this work, an effective strategy to form a hole‐selective layer using phenethylammonium iodide (PEAI) salt is presented that demonstrates unprecedently high open‐circuit voltage of 0.9 V with 18 µW cm⁻² under 200 lux (cool white light‐emitting diodes). An appropriate post‐deposited amount of PEAI (2 mg) strongly interacts with the perovskite surface forming a conformal coating of PEAI on the perovskite film surface, which improves the crystallinity and absorption of the film. Here, Kelvin probe force microscopy results indicate the diminished potential difference across the grain boundaries and grain interiors after the PEAI deposition, constructing an electrically and chemically homogeneous surface. Also, the surface becomes more p‐type with a downshift of a valence band maximum, confirmed by ultraviolet photoelectron spectroscopy measurement, facilitating the transport of holes to the hole transport layer (HTL). The hole‐selective layer‐deposited devices exhibit reduced hysteresis in light current density–voltage curves and maintain steadily high fill factor across the different light intensities (200–1000 lux). This work highlights the importance of the HTL/perovskite interface that prepares the indoor halide perovskite PV devices for powering IoT device.

A 2D zinc‐based metal–organic frameworks (MOFs) with plenty of active sites are prepared through a molecular self‐assembly strategy and used to solve the incompatibility between MOFs and perovskite films. The tunable crystallographic orientation and functionalized framework of this material are considered for regulating the photovoltaic performance and stability of perovskite solar cells.

Abstract

Perovskite degradation induced by surface defects and imperfect grain boundaries of films seriously damages the performance of perovskite solar cells (PSCs). Meanwhile, conventional organic molecules cannot maintain the long‐time passivation effects under the stimulation of external environmental factors. Here, efficient and stable grain passivation in perovskite films is realized by preparing formic acid‐functionalized 2D metal–organic frameworks (MOFs) as the terminated agent. Through robust interactions between exposed active sites and PbI₂, the 2D MOFs tightly caps the surface of PbI₂‐terminated perovskite grains to stabilize the perovskite phases and aids the adhesion of adjacent grains. The MOFs mainly distributed at the grain boundaries of the perovskite film is directly observed at the microscopic scale. The modified perovskite films have regular morphology, lower defect density, and superior optoelectronic properties. Benefiting from the suppressed charge recombination and faster charge extraction, a power conversion efficiency of 21.28% is achieved for the best‐performing PSC device. The unencapsulated PSCs with the MOFs modification maintain 88% and 81% of their initial efficiency after 750 h heating at 85 °C under N₂ atmosphere and more than 1000 h storage in ambient environment (25 °C, RH ≈ 40%), respectively.

Aided by theoretical calculations, a multifunctional 2,2‐difluoropropanediamide (DFPDA) molecule that bears carbonyl, amino, and fluorine groups is first introduced into the perovskite precursor, serving as a crystal growth mitigator, grain boundaries passivator, and surface protection material. With the help of the combined effects of multifunctional groups in DFPDA, the perovskite cells deliver an efficiency of 22.21% and improved stability.

Abstract

With a certified efficiency as high as 25.2%, perovskite has taken the crown as the highest efficiency thin film solar cell material. Unfortunately, serious instability issues must be resolved before perovskite solar cells (PSCs) are commercialized. Aided by theoretical calculation, an appropriate multifunctional molecule, 2,2‐difluoropropanediamide (DFPDA), is selected to ameliorate all the instability issues. Specifically, the carbonyl groups in DFPDA form chemical bonds with Pb²⁺ and passivate under‐coordinated Pb²⁺ defects. Consequently, the perovskite crystallization rate is reduced and high‐quality films are produced with fewer defects. The amino groups not only bind with iodide to suppress ion migration but also increase the electron density on the carbonyl groups to further enhance their passivation effect. Furthermore, the fluorine groups in DFPDA form both an effective barrier on the perovskite to improve its moisture stability and a bridge between the perovskite and HTL for effective charge transport. In addition, they show an effective doping effect in the HTL to improve its carrier mobility. With the help of the combined effects of these groups in DFPDA, the PSCs with DFPDA additive achieve a champion efficiency of 22.21% and a substantially improved stability against moisture, heat, and light.

The time‐resolved grazing‐incidence wide‐angle X‐ray scattering technique provides real‐time insights on the phase‐transition during the organic cation coating and perovskite quantum wells (PQWs)/3D architecture formation mechanism. With fluorinated poly(triarylamine) (PTAA) as a dopant‐free hole‐transport layer, this PQWs/3D architecture leads to stable perovskite photovoltaics with power conversion efficiency of >22%.

Abstract

The combination of a bulk 3D perovskite layer and a reduced dimensional perovskite layer (perovskite quantum wells (PQWs)) is demonstrated to enhance the performance of perovskite solar cells (PSCs) significantly in terms of stability and efficiency. This perovskite hierarchy has attracted intensive research interest; however, the in‐depth formation mechanism of perovskite quantum wells on top of a 3D perovskite layer is not clearly understood and is therefore the focus of this study. Along with ex situ morphology and photophysical characterization, the time‐resolved grazing‐incidence wide‐angle X‐ray scattering (TS‐GIWAXS) technique performed in this study provides real‐time insights on the phase‐transition during the organic cation (HTAB ligand molecule) coating and PQWs/3D architecture formation process. A strikingly strong ionic reaction between the 3D perovskite and the long‐chain organic cation leads to the quick formation of an ordered intermediate phase within only a few seconds. The optimal PQWs/3D architecture is achieved by controlling the HTAB casting, which is assisted by time‐of‐flight SIMS characterization. By controlling the second ionic reaction during the long‐chain cation coating process, along with the fluorinated poly(triarylamine) (PTAA) as a hole‐transport layer, the perovskite solar cells demonstrate efficiencies exceeding 22% along with drastically improved device stability.

This work presents effective grain boundary defect passivation in a 1.78 eV quadruple cation wide‐bandgap perovskite using a combination of two approaches for passivation: four cations (RbCsFAMA) and secondary growth (by guanidinium iodide) to achieve high efficiency.

Development of high‐performance wide‐bandgap perovskites is a key component to enable tandem solar cells with either a silicon or low‐bandgap perovskites. However, the presence of defects in the Br‐rich wide‐bandgap perovskites, especially in the grain boundaries (GBs) has been particularly challenging and limits its performance. Herein, to accomplish the passivation of these defects, a combination of cation management with rubidium (Rb) introduction into the triple cation combination of cesium/formamidinium/methylammonium (CsFAMA) is exercised. Passivation is further enhanced by secondary growth (SG) using guanidinium iodide. In‐depth assessments of GB defect passivation are performed using Kelvin probe force microscopy (KPFM) and nanoscale charge‐carrier dynamics mappings provide insightful details on the presence of GBs defects and their suppression by the cation management and SG techniques. Reduction of unreacted PbX₂ to realize a highly crystalline perovskite surface is achieved after incorporating Rb and SG treatment. As a result, a champion cell for 1.78 eV (FA_0.79MA_0.16Cs_0.05)_0.95Rb_0.05Pb(I_0.6Br_0.4)₃ wide‐bandgap perovskite with an efficiency of 17.71% along with enhancement in all photovoltaic parameters is achieved. This study introduces a new way to analyze GB defects and reveals the consequence of defect passivation on charge‐carrier dynamics for realizing efficient perovskites.

A new pyridine‐based polymer semiconductor (PPY2) was introduced as the dopant‐free hole‐transporting material in inverted perovskite solar cells. It exhibits suitable energy levels, high hole mobility, effective passivation effects, and the capability of promoting the formation of a high‐quality polycrystalline perovskite film. The devices based on PPY2 delivered an encouraging power‐conversion efficiency up to 22.41 % with a high V _OC of 1.16 V.

Abstract

Currently, the performance improvement for inverted perovskite solar cells (PVSCs) is mainly limited by the high open circuit voltage (V _OC) loss caused by detrimental non‐radiative recombination (NRR) processes. Herein, we report a simple and efficient way to simultaneously reduce the NRR processes inside perovskites and at the interface by rationally designing a new pyridine‐based polymer hole‐transporting material (HTM), PPY2, which exhibits suitable energy levels with perovskites, high hole mobility, effective passivation of the uncoordinated Pb²⁺ and iodide defects, as well as the capability of promoting the formation of high‐quality polycrystalline perovskite films. In absence of any dopants, the inverted PVSCs using PPY2 as the HTM deliver an encouraging PCE up to 22.41 % with a small V _OC loss (0.40 V), among the best device performances for inverted PVSCs reported so far. Furthermore, PPY2‐based unencapsulated devices show an excellent long‐term photostability, and over 97 % of its initial PCE can be maintained after one sun constant illumination for 500 h.