shuhui

Inspired by the competitive growth in forests, a competitive growth mechanism‐driven perovskite grain growth approach via CD disk printing wettability‐patterned substrates is proposed to achieve large grain size and avoid the discontinuous perovskite films caused by the nonwettability of substrates, resulting in efficiencies over 20% for the micro‐contact print perovskite solar cells.

Abstract

Novel photovoltaic perovskite solar cells (PSCs) with high‐efficient photovoltaic property are largely in thrall to the uncertain perovskite grain size and inevitable defects. Here, inspired by the competitive growth between tree and grass in the forest system, a competitive perovskite grain growth approach via micro‐contact print (MicroCP) method (CD disk as templates) for printing wettability‐patterned substrate is proposed, aiming to achieve large‐grained perovskite and avoid discontinuous perovskite films caused by the low wettability of substrates. A MicroCP process is employed to construct a patterned wettability surface for the perovskite competitive growth mechanism on the electrode surface. This approach modifies the substrates quickly, ensures the uniform coverage of perovskite due to the function of ‐NH₂ and Pb²⁺ bonds, and converts the perovskite films composed of small grains and pinholes into high‐quality perovskite films, free from pinholes and made up of large grains, resulting in efficiencies over 20% for the MicroCP PSCs.

Crystalline DRCN5T is used to optimize the performance of thick‐film ternary organic solar cells by forming obvious interpenetrating network morphology with decreased π‐π stacking and enhanced domain purity. More importantly, DRCN5T can precisely modulate vertical distribution of the active layer due to contrasting miscibility with PTB7‐Th and PC₇₀BM, which drives the enrichment of PTB7‐Th on the active layer surface.

Abstract

Blending multidonor or multiacceptor organic materials as ternary devices has been recognized as an efficient and potential method to improve the power conversion efficiency of bulk heterojunction devices or single‐junction components in tandem design. In this work, a highly crystalline molecule, DRCN5T, is involved into a PTB7‐Th:PC₇₀BM system to fabricate large‐area organic solar cells (OSCs) whose blend film thickness is up to 270 nm, achieving an impressive performance of 11.1%. The significant improvement of OSCs after adding DRCN5T is due to the formation of an interconnected fibrous network with decreased π–π stacking and enhanced domain purity, in addition to the optimized vertical distribution of PTB7‐Th and PC₇₀BM, producing more effective charge separation, transport, and collection. The optimized morphology and performance are actually determined by the miscibility in different components, which can be quantitatively described by the Flory–Huggins interaction parameter of −0.80 and 2.94 in DRCN5T:PTB7‐Th and DRCN5T:PC₇₀BM blends, respectively. The findings in this work can potentially guide the selection of an appropriate third additive for high‐performance OSCs for the sake of large‐area printing and roll‐to‐roll fabrication from the view of miscibility.

A water‐based TiO₂ nanocrystal solution is developed to use as an electron transport layer for perovskite solar cells that show substantially reduced organic molecules and a high Cl content on the TiO₂ nanocrystal surface, which effectively passivate the interface between TiO₂ and perovskite layer with significantly reduced defects. Corresponding solar cells demonstrate a 20.5% power conversion efficiency and 500 h of operational stability.

Halide perovskite solar cells (PSCs) provide a new opportunity for next‐generation photovoltaic applications. However, traditional low‐temperature solution‐processed TiO₂ that acts as an electron transport layer for PSCs shows an inferior stability compared with solar cells based on high‐temperature (typically 500 °C) TiO₂; however, the high‐temperature process is energy consuming and is not compatible with flexible device processing. Traditional TiO₂ nanoparticles made from titanium tetrachloride dispersed in an organic solvent usually have many organic molecules attached on their surface that lead to the formation of deep‐level defect states during long‐term operations. Herein, environmentally friendly, water‐based Cl‐passivated TiO₂ nanoparticles (W‐TiO₂) are invented, and surface organic molecules are removed by a vacuum rotary evaporation process. W‐TiO₂‐based PSCs can reach up to a 20.5% power conversion efficiency with reduced hysteresis and can maintain 80% of their initial performance after 500 h of continuous operation under 1 sun illumination at the maximum power point. This improved performance is ascribed to the organic‐molecule‐free and Cl‐passivated surfaces. The water‐based TiO₂ nanoparticle dispersion also offers a convenient and universal way to introduce other passivation agents to further improve the photovoltaic performance of PSCs.

In situ synthesis of polycrystalline SnO₂ electron‐transfer layers (ETLs) at temperatures as low as 130 °C is developed. The best efficiency of devices fabricated using these ETLs is up to 20.52% for those based on glass and 18% for those based on a flexible substrate, among the best for planar n–i–p‐type perovskite (MAPbI₃) solar cells.

Abstract

A high‐quality polycrystalline SnO₂ electron‐transfer layer is synthesized through an in situ, low‐temperature, and unique butanol–water solvent‐assisted process. By choosing a mixture of butanol and water as a solvent, the crystallinity is enhanced and the crystallization temperature is lowered to 130 °C, making the process fully compatible with flexible plastic substrates. The best solar cells fabricated using these layers achieve an efficiency of 20.52% (average 19.02%) which is among the best in the class of planar n–i–p‐type perovskite (MAPbI₃) solar cells. The strongly reduced crystallization temperature of the materials allows their use on a flexible substrate, with a resulting device efficiency of 18%.

Two perylene diimide (PDI)–based small molecular acceptors containing a 3D Alq₃ core flanked by PDI or PDI2 end units are developed for efficient polymer solar cells. The coordination between Alq₃ and the newly used 4,4′‐bipyridine additive allows a high fill factor, power conversion efficiency, and stability to be simultaneously achieved in PDI‐based polymer solar cells.

Abstract

Two novel perylene diimide (PDI)–based derivatives, Alq₃‐PDI and Alq₃‐PDI2, are synthesized by flanking a 3D tri(8‐hydroxyquinoline)aluminum(III) (Alq₃) core with PDI and a helical PDI dimer (PDI2) to construct high‐performance small molecular nonfullerene acceptors (SMAs). The 3D Alq₃ core significantly suppresses the molecular aggregation of the resulting SMAs, leading to a well‐mixed blend with a PTTEA donor polymer and weak phase separation. Compared with Alq₃‐PDI, the extended π‐conjugation of Alq₃‐PDI2 results in higher‐order molecular packing, which improves the absorption and phase separation behavior. Thus, the Alq₃‐PDI2 devices have higher J _sc and FF values and better device performance, which are further enhanced by a small amount of 4,4′‐bipyridine (Bipy) as an additive. The coordination between Bipy and the Alq₃ core promotes molecular packing and phase separation, which lower charge recombination and enhanced charge collection in the resulting devices. Therefore, a largely improved J _sc of 15.74 mA cm⁻² and very high FF of 71.27% are obtained in the Alq₃‐PDI2 devices, resulting in a power conversion efficiency of 9.54%, which is the best value reported for PDI‐based polymer solar cells. The coordination can also serve as a “molecular lock,” which prevents molecular motion and thus improves device stability.

The long‐term photostability under AM1.5G simulated 1 sun illumination including UV is demonstrated with the perovskite solar cell exceeding power conversion efficiency of 20%. This achievement stems from understanding the role of oxygen on the degradation under illumination. Oxygen induces iodine migration from the perovskite to a hole transport layer, which interrupts the charge transport through the interface.

Abstract

Perovskite solar cells (PSCs) with mesoporous TiO₂ (mp‐TiO₂) as the electron transport material attain power conversion efficiencies (PCEs) above 22%; however, their poor long‐term stability is a critical issue that must be resolved for commercialization. Herein, it is demonstrated that the long‐term operational stability of mp‐TiO₂ based PSCs with PCE over 20% is achieved by isolating devices from oxygen and humidity. This achievement attributes to systematic understanding of the critical role of oxygen in the degradation of PSCs. PSCs exhibit fast degradation under controlled oxygen atmosphere and illumination, which is accompanied by iodine migration into the hole transport material (HTM). A diffusion barrier at the HTM/perovskite interface or encapsulation on top of the devices improves the stability against oxygen under light soaking. Notably, a mp‐TiO₂ based PSC with a solid encapsulation retains 20% efficiency after 1000 h of 1 sun (AM1.5G including UV) illumination in ambient air.

Publication date: 18 September 2019

Source: Joule, Volume 3, Issue 9

Author(s): Axel F. Palmstrom, Giles E. Eperon, Tomas Leijtens, Rohit Prasanna, Severin N. Habisreutinger, William Nemeth, E. Ashley Gaulding, Sean P. Dunfield, Matthew Reese, Sanjini Nanayakkara, Taylor Moot, Jérémie Werner, Jun Liu, Bobby To, Steven T. Christensen, Michael D. McGehee, Maikel F.A.M. van Hest, Joseph M. Luther, Joseph J. Berry, David T. Moore

Context & Scale

Summary

Graphical Abstract

10% Pb reduction in CsPb_0.9Zn_0.1I₂Br boosts the efficiency of the solar cell device. Zn²⁺ results in high quality crystalline and energy state modulation, greatly reducing the trap states and promoting the charge transport in the device. This work highlights that Zn is an effective and stable Pb reducer that compares well to the chemical unstable Sn, in efficient CsPbX₃ based PSCs.

Abstract

Fabrication of efficient Pb reduced inorganic CsPbI₂Br perovskite solar cells (PSC) are an important part of environment‐friendly perovskite technology. In this work, 10% Pb reduction in CsPb_0.9Zn_0.1I₂Br promotes the efficiency of PSCs to 13.6% (AM1.5, 1sun), much higher than the 11.8% of the pure CsPbI₂Br solar cell. Zn²⁺ has stronger interaction with the anions to manipulate crystal growth, resulting in size‐enlarged crystallite with enhanced growth orientation. Moreover, the grain boundaries (GBs) are passivated by the Cs‐Zn‐I/Br compound. The high quality CsPb_0.9Zn_0.1I₂Br greatly diminishes the GB trap states and facilitates the charge transport. Furthermore, the Zn4s‐I5p states slightly reduce the energy bandgap, accounting for the wider solar spectrum absorption. Both the crystalline morphology and energy state change benefit the device performance. This work highlights a nontoxic and stable Pb reduction method to achieve efficient inorganic PSCs.

Propane‐1,3‐diammonium cations are first adopted to construct cesium–formamidinium (Cs–FA) perovskite solar cells (PSCs) with an efficiency of 18.1% and much enhanced device stability, and the opposing effects induced by the diammonium cation are resolved.

Incorporating diammonium cations, which electrostatically connect the adjacent inorganic slabs ([PbI₆]⁴⁻), into 3D perovskite is recently proposed to develop high‐performance perovskite solar cells (PSCs). However, due to limited studies, the effects of these organic cations on the perovskite structural and optoelectronic properties are yet to be understood. Herein, a diammonium cation, propane‐1,3‐diammonium (PDA), is first proposed to modulate the cesium–formamidinium (Cs–FA)‐mixed cation perovskite. By increasing the PDA content, the efficiency of the Cs_0.15FA_{0.85 − x} PDA _x PbI₃ PSC first increases and then drastically decreases. The highest power conversion efficiency (PCE) of 18.10% obtained by Cs_0.15FA_0.83PDA_0.02PbI₃ is superior to that of the Cs_0.15FA_0.85PbI₃ (16.82%). Through systematic investigations, it is revealed that the PDA content–dependent efficiency is attributed to a competition between the enhanced defect passivation and emerged excitonic effect with an increased PDA content. Moreover, the encapsulated Cs_0.15FA_0.83PDA_0.02PbI₃ device exhibits almost 1.5 times increased stability than the Cs_0.15FA_0.85PbI₃ counterpart, with 83% of its initial efficiency retained after 500 h exposure, under continuous light soaking at 60 °C in ambient air. This study provides a practical strategy to enhance the device stability without sacrificing the efficiency and deepens our understanding on effects of diammonium cation incorporated in 3D perovskite.

The long‐term photostability under AM1.5G simulated 1 sun illumination including UV is demonstrated with the perovskite solar cell exceeding power conversion efficiency of 20%. This achievement stems from understanding the role of oxygen on the degradation under illumination. Oxygen induces iodine migration from the perovskite to a hole transport layer, which interrupts the charge transport through the interface.

Abstract

Perovskite solar cells (PSCs) with mesoporous TiO₂ (mp‐TiO₂) as the electron transport material attain power conversion efficiencies (PCEs) above 22%; however, their poor long‐term stability is a critical issue that must be resolved for commercialization. Herein, it is demonstrated that the long‐term operational stability of mp‐TiO₂ based PSCs with PCE over 20% is achieved by isolating devices from oxygen and humidity. This achievement attributes to systematic understanding of the critical role of oxygen in the degradation of PSCs. PSCs exhibit fast degradation under controlled oxygen atmosphere and illumination, which is accompanied by iodine migration into the hole transport material (HTM). A diffusion barrier at the HTM/perovskite interface or encapsulation on top of the devices improves the stability against oxygen under light soaking. Notably, a mp‐TiO₂ based PSC with a solid encapsulation retains 20% efficiency after 1000 h of 1 sun (AM1.5G including UV) illumination in ambient air.

Symmetry breaking provides a new material design strategy for nonfullerene small molecule acceptors (SMAs). The past 10 years have witnessed significant advances in asymmetric nonfullerene SMAs in organic solar cells (OSCs). In this review, the progress of asymmetric nonfullerene SMAs is reviewed. The structure–property relationships and the perspectives for future development of asymmetric non‐fullerene SMAs are also discussed.

Abstract

Symmetry breaking provides a new material design strategy for nonfullerene small molecule acceptors (SMAs). The past 10 years have witnessed significant advances in asymmetric nonfullerene SMAs in organic solar cells (OSCs) with power conversion efficiency (PCE) increasing from ≈1% to ≈14%. In this review, the progress of asymmetric nonfullerene SMAs, including early reports of asymmetric nonfullerene SMAs, asymmetric PDI‐based nonfullerene SMAs, and asymmetric acceptor–donor–acceptor (A–D–A)‐type nonfullerene SMAs, is summarized. The structure–property relationships and the perspectives for future development of asymmetric nonfullerene SMAs are also discussed.

Nature Communications, Published online: 14 May 2019; doi:10.1038/s41467-019-10098-z

Herein, the open‐circuit voltage losses and bias‐dependent photo‐ and electroluminescence of high‐performance 2D/3D perovskite solar cells, which exhibit outstanding optoelectronic properties, are investigated. These are state‐of‐the‐art photovoltaic devices. Results suggest that by reducing nonradiative recombination processes in the absorber, the power conversion efficiency of the studied photovoltaic devices can be improved.

Herein, the optoelectronic properties of interface‐engineered perovskite 2D|3D‐heterojunction structure solar cells are reported. The reciprocity theorem is applied to determine the maximum open‐circuit voltage (V _oc) the device can deliver under solar illumination. A V _oc of 1.295 V is found, analyzing the measured external quantum efficiency and assuming only radiative recombination. For comparison, the experimental open‐circuit voltage found for the studied 2D|3D heterojunctions is 1.15 V. The contribution of nonradiative recombination is explored by measuring the electroluminescence quantum yield. A quantum yield of 0.4% is found at current densities equivalent to 1 sun illumination. This translates into a V _oc loss of ≈140 mV, which is in very good agreement with the experimental findings. In addition, the fundamental correlation between luminescence intensity and the chemical potential predicted by the generalized Planck law is confirmed for the photoluminescence measured at different light intensities when the device is operated under open‐circuit conditions and for the electroluminescence when operated under a forward bias. The investigations in this study suggest that further efficiency improvements can be achieved by reducing the nonradiative recombination in the studied solar cell. At the same time, a high‐performance near IR light emitting diode can be realized.

Efficient electron transport layer‐free perovskite solar cells (ETL‐free PSCs) with cost‐effective and simplifed design can greatly promote the large area flexible application of PSCs. Within this review, the recent advancement, key issues, working mechanism, existing problems, and future direction of ETL‐free PSCs are summarized.

Abstract

Perovskite solar cells (PSCs) have shown great potential for photovoltaic applications with their unprecedented power conversion efficiency advancement. Such devices generally have a complex structure design with high temperature processed TiO₂ as the electron transport layer (ETL). Further careful design of device configuration to fully tap the potentials of perovskite materials is expected. Particularly, for the practical application of PSCs, it is crucial to simplify their device structures thus the associated manufacturing process and cost while maintaining their efficiency to be comparable with the conventional devices. But how simple is simple? ETL‐free PSCs promise the simplest structured, thus simple manufacturing processes and low cost large area PSCs in practical applications. They can also help the further exploration of the great potential of perovskite materials and understanding the working principle of PSCs. Within this review, the evolution of the PSC is outlined by discussing the recent advances in the simplification of device configuration and processes for cost effective, highly efficient, and robust PSCs, with a focus on ETL‐free PSCs. Their advancement, key issues, working mechanism, existing problems, and future performance enhancements. This review aims to promote the future development of low cost and robust ETL‐free PSCs toward more efficient power output.

By coating n‐butylammonium bromide on wide‐bandgap double‐cation perovskite absorber layers (E _G ≈ 1.72 eV), a thin 2D Ruddlesden–Popper perovskite layer of intermediate phase is formed. The resulting heterostructure mitigates nonradiative recombination and enables a high open‐circuit voltage of up to 1.31 V and stable power output efficiencies of up to 19.4%.

Abstract

In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (V _OC) of 1.31 V. The V _OC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic−inorganic hybrid perovskite solar cells and the V _OC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, V _OC is enhanced by 80 mV.

Surface‐clean and highly crystalline SnO₂ ETL is fabricated by a simple hydrothermal treatment at temperatures as low as 100 °C. The perovskite solar cells based on this hydrothermally treated SnO₂ ETL exhibit a champion PCE of 20.3% on a rigid ITO/Glass substrate, and a champion PCE of 18.1% and certified PCE of 17.3% on a flexible ITO/PEN substrate.

Abstract

Perovskite solar cells (PSCs) are one of the most promising solar energy conversion technologies owing to their rapidly developing power conversion efficiency (PCE). Low‐temperature solution processing of the perovskite layer enables the fabrication of flexible devices. However, their application has been greatly hindered due to the lack of strategies to fabricate high‐quality electron transport layers (ETLs) at the low temperatures (≈100 °C) that most flexible plastic substrates can withstand, leading to poor performances for flexible PSCs. In this work, through combining the spin‐coating process with a hydrothermal treatment method, ligand‐free and highly crystalline SnO₂ ETLs are successfully fabricated at low temperature. The flexible PSCs based on this SnO₂ ETL exhibit an excellent PCE of 18.1% (certified 17.3%). The flexible PSCs maintained 85% of the initial PCE after 1000 bending cycles and over 90% of the initial PCE after being stored in ambient air for 30 days without encapsulation. The investigation reveals that hydrothermal treatment not only promotes the complete removal of organic surfactants coated onto the surface of the SnO₂ nanoparticles by hot water vapor but also enhances crystallization through the high vapor pressure of water, leading to the formation of high‐quality SnO₂ ETLs.

High‐performance inverted lead‐free perovskite solar cells (PVSCs) with enhanced UV stability are demonstrated via grain boundaries modification by PTN‐Br. The gradient band alignment of FASnI₃ films with a PEDOT:PSS hole‐transport layer ensures excellent hole transportation and higher open‐circuit voltage. This study provides a strategy to develop high‐performance tin‐based PVSCs based on balanced charge transportation and reduced trap states.

Abstract

High electronic quality perovskite films with a balanced charge transportation is critical for satisfying high‐performance for perovskite solar cells (PVSCs). However, the inferior band alignment of tin‐based perovskite films with an adjacent hole‐transport layer (HTL) leads to a poor hole transportation and collection. In this work, the semiconducting molecule poly[tetraphenylethene 3,3′‐(((2,2‐diphenylethene‐1,1‐diyl)bis(4,1‐phenylene))bis(oxy))bis(N,N‐dimethylpropan‐1‐amine)tetraphenylethene] (PTN‐Br) is introduced into a lead‐free perovskite precursor to form a bulk heterojunction film. In addition, the PTN‐Br molecule with the suitable highest occupied molecular orbital energy level (−5.41 eV) can fill into the grain boundaries of the perovskite film, serving as a hole‐transport medium between grains. The gradient band alignment of the perovskite film with poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL ensures excellent hole transportation and higher open‐circuit voltage. In addition, the π‐conjugated polymer PTN‐Br can passivate trap states within the perovskite film due to the formation of Lewis adducts between uncoordinated Sn atoms and the dimethylamino of PTN‐Br. Consequently, a champion efficiency of 7.94% is achieved with significant enhancements in the open‐circuit voltage and fill factor. Furthermore, the PTN‐Br incorporated device shows better ultra violet (UV) stability because of the UV barrier and passivating effect of PTN‐Br, retaining about 66% of its initial efficiency after 5 h of continuous UV light irradiation.

Publication date: August 2019

Source: Nano Energy, Volume 62

Author(s): Jing Yu, Mingdun Liao, Di Yan, Yimao Wan, Hao Lin, Zilei Wang, Pingqi Gao, Yuheng Zeng, Baojie Yan, Jichun Ye

Graphical abstract

Effective passivation over c-Si substrates by electron beam deposited MgO_x followed by a low-temperature post-annealing and an alumina-initiated atomic hydrogen passivation has been achieved. a PERC-like dopant-free rear contact with 1 nm-MgO_x as electron-transporting layer and 10 nm-MgO_x as passivating layer was fabricated to underscore the great potential of MgO_x passivating contact.

Organic n‐type materials as electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs) have attracted many scientists' attention, not only because of their several advantages, including easy synthesis, tunable frontier molecular orbitals, decent electron mobility, and reasonable chemical/thermal stability, but also because of their ability to make large‐scale solution‐processing p–i–n PSCs possible.

Abstract

Organic n‐type materials (e.g., fullerene derivatives, naphthalene diimides (NDIs), perylene diimides (PDIs), azaacene‐based molecules, and n‐type conjugated polymers) are demonstrated as promising electron transport layers (ETLs) in inverted perovskite solar cells (p–i–n PSCs), because these materials have several advantages such as easy synthesis and purification, tunable frontier molecular orbitals, decent electron mobility, low cost, good solubility in different organic solvents, and reasonable chemical/thermal stability. Considering these positive factors, approaches toward achieving effective p–i–n PSCs with these organic materials as ETLs are highlighted in this Review. Moreover, organic structures, electron transport properties, working function of electrodes caused by ETLs, and key relevant parameters (PCE and stability) of p–i–n PSCs are presented. Hopefully, this Review will provide fundamental guidance for future development of new organic n‐type materials as ETLs for more efficient p–i–n PSCs.

The small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide is explored as cathode interfacial material to reduce the extraction barrier between phenyl‐C61‐butyric acid methyl ester and Ag. With the better contact quality thanks to this molecule, both opaque and semitransparent p‐i‐n perovskite solar cell achieve improved performance and stability.

Abstract

Metal halide perovskite solar cells (PSCs) in the inverted planar p‐i‐n configuration often employ phenyl‐C61‐butyric acid methyl ester (PC₆₁BM) as electron transport layer, onto which Ag is deposited as outer electrode. However, the energy offset between PC₆₁BM and Ag imposes an energy barrier for electron extraction. In this work, to improve the contact quality of this stack, a small organic molecule (2‐(1,10‐phenanthrolin‐3‐yl)naphth‐6‐yl)diphenylphosphine oxide (DPO) as a cathode interfacial material (CIM), inserted between PC₆₁BM and Ag, is introduced. In devices with the indium tin oxide (ITO)/NiO _x /methylammonium lead iodide (MAPbI₃)/PC₆₁BM/CIM/Ag configuration, it is found that this results in fill factor (FF) and short‐circuit current density values (J _SC) that are up to ≈34% and ≈1 mA cm⁻² higher, respectively, compared to DPO‐free devices. Inserting additional thin ZnO nanoparticle layers further improves the contact quality, leading to a power conversion efficiency of 18.2%. Semitransparent PSCs, utilizing DPO as an interlayer buffer layer are also realised. Resultant devices exhibit improved performance compared to DPO‐free devices. This proves that DPO withstands the sputtering of ITO, and may thus find application in perovskite‐based tandem devices. It is concluded that DPO acts as an excellent cathode modifier, opening new device‐engineering opportunities for p‐i‐n PSCs, especially in their semitransparent implementation.

Embracing perovskite grains in a soft fullerene network represents a new and scalable approach, to make perovskite mechanically stable and thus compatible with flexible substrates. The method is demonstrated to prepare flexible perovskite solar cells with the highest ever reported power conversion efficiency. The superior mechanical stability from device performance under working conditions is characterized in situ.

Abstract

Halide perovskite films processed from solution at low‐temperature offer promising opportunities to make flexible solar cells. However, the brittleness of perovskite films is an issue for mechanical stability in flexible devices. Herein, photo‐crosslinked [6,6]‐phenylC₆₁‐butyric oxetane dendron ester (C‐PCBOD) is used to improve the mechanical stability of methylammonium lead iodide (MAPbI₃) perovskite films. Also, it is demonstrated that C‐PCBOD passivates the grain boundaries, which reduces the formation of trap states and enhances the environmental stability of MAPbI₃. Thus, MAPbI₃ perovskite solar cells are prepared on solid and flexible substrates with record efficiencies of 20.4% and 18.1%, respectively, which are among the highest ever reported for MAPbI₃ on both flexible and solid substrates. The result of this work provides a step improvement toward stable and efficient flexible perovskite solar cells.