Chen Weijie

Energy‐dispersive X‐ray spectroscopy in a scanning transmission electron microscope (STEM‐EDX) is performed on perovskite solar cells with methodically varied acquisition parameters to examine the relationship between electron dose, data quality, and beam damage. Five metrics are defined to quantify the statistical uncertainty in the STEM‐EDX data and extent of beam damage.

Abstract

Quantitative chemical analysis on the nanoscale provides valuable information on materials and devices which can be used to guide further improvements to their performance. In particular, emerging families of technologically relevant composite materials such as organic–inorganic hybrid halide perovskites and metal‐organic frameworks stand to benefit greatly from such characterization. However, these nanocomposites are also vulnerable to damage induced by analytical probes such as electron, X‐ray, or neutron beams. Here the effect of electrons on a model hybrid halide perovskite is investigated, focusing on the acquisition parameters appropriate for energy‐dispersive X‐ray spectroscopy in a scanning transmission electron microscope (STEM‐EDX). The acquisition parameters are systematically varied to examine the relationship between electron dose, data quality, and beam damage. Five metrics are outlined to assess the quality of STEM‐EDX data and severity of beam damage, further validated by dark field STEM imaging. Loss of iodine through vacancy creation is found to be the primary manifestation of electron beam damage in the perovskite specimen, and iodine content is seen to decrease exponentially with electron dose. This work demonstrates data acquisition and analysis strategies that can be used for studying electron beam damage and for achieving reliable quantification for a broad range of beam‐sensitive materials.

An additive‐involved leaching method is proposed to reduce the preparation temperature of CsPbI₃ to 100 °C. The CsPbI₃ perovskite film with high crystallinity is formed by an ion exchange reaction between DMAPbI₃ and Cs₄PbI₆. More than 16% photoelectric conversion efficiency can be achieved and the inencapsulation device exhibits remaekable stability.

Abstract

Inorganic CsPbI₃ perovskite with an optical bandgap ranging from 1.67 to 1.75 eV is a promising light‐harvesting material as a top cell in tandem solar cells, but its high fabrication temperature can damage the middle layers or the bottom subcells. Here, an additive‐involved leaching method to fabricate CsPbI₃ perovskite films is demonstrated, which can decrease the preparation temperature to 100 °C. The CsPbI₃ perovskite films with high crystallinity are achieved by a solution assisted reaction between DMAPbI₃ and Cs₄PbI₆ with the leaching of DMA⁺, Cs⁺, and I⁻. The as‐prepared CsPbI₃ perovskite films exhibit much superior stability compared to their high‐temperature counterparts. As a result, a power conversion efficiency of over 16% is obtained, and the unencapsulated device maintains over 93% of the initial efficiency after aging for 30 days in air with a relative humidity of 10%.

Comprehensive experimental and theoretical evidence is presented to elucidate the charge carrier recombination in mesoscopic perovskite solar cells (PSC). The spatially decoupled electron and hole migration inside the nanoporous charge extraction scaffold is examined by a 2D electrical model that explains the remarkably high photovoltages achieved in hole extraction layer‐free, carbon–graphite‐based PSCs.

A physical model to explain the 2D charge recombination in mesoscopic graphite‐based perovskite solar cells (PSCs) having a highly selective front electrode and a nonselective back electrode is presented. Steady‐state photovoltage and photoluminescence (PL) as well as transient PL are studied for a wide range of device configurations, providing insights in the interface recombination at the front and back contact, namely, the mesoporous titania (m‐TiO₂) and the graphite layer. Combining experimental evidence with the first 2D simulation of a perovskite solar cell, it is found that the characteristic thick absorber layer of mesoscopic graphite‐based PSC is a necessity to enhance the photovoltage. This is because the interface recombination at the back contact is a diffusion‐limited process. The electrode spacing should, however, not be enhanced by increasing the perovskite/m‐TiO₂ thickness as this increases surface recombination losses at this interface. The study determines design rules for the optimal geometry of the mesoporous layers and helps to identify the limiting recombination pathways for an improvement of future device architectures.

Fe(III) ion grafted metal–organic complexes (Fe(III)⊂MOCs) are introduced as p‐type dopants into hole transport layers (HTLs), contributing to outstanding n–i–p perovskite solar cells (PSCs) with improved power conversion efficiency (PCE, 20.46%), reduced J–V hysteresis, and enhanced air stability, which is significantly superior to the reference devices.

Realizing the rapid/controllable oxidation of 2,2′,7,7′‐tetrakis(N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spirobifluorene (Spiro‐OMeTAD) under an inert atmosphere, reducing the J–V hysteresis and enhancing the air stability of devices is extremely significant to fabricate high‐performance perovskite solar cells (PSCs). Herein, the Fe(III) ion grafted metal–organic complexes (Fe(III) ⊂ MOCs) are assembled and used as the p‐type dopants of hole transport layers (HTLs) to prepare efficient and stable PSCs. Consequently, the optimal Fe(III) ⊂ In‐2‐bpydc‐doped device presents a significantly enhanced power conversion efficiency (PCE) of 20.46%, benefitting from the improved hole extraction and weakened carrier recombination at the interface between HTLs and perovskite films. More importantly, the modified device possesses a reduced J–V hysteresis index (HI) of 0.094, and can maintain nearly 90% of its initial PCE value after being exposed to the air at ≈25 °C and relative humidity (RH) of ≈35% for 4 weeks, which is attributed to the restrained detrimental penetration behavior by the MOC carrier part of dopants. This work is of important guiding significance for the application of MOC materials in photovoltaic fields.

State‐of‐the‐art perovskite and organic solar cells use inorganic hole transport materials (HTMs) due to their superior electronic properties. These HTMs are, however, expensive and prone to degradation. A range of robust inorganic HTMs are emerging, that provide a trade‐off between efficiency, stability, and cost, and are critically reviewed herein.

Interfaces in perovskite and organic solar cells play a central role in advancing efficiency and prolong device durability. They improve charge transport/transfer from the absorber layer to the collecting electrodes, while also blocking the opposite charge carriers, minimize voltage losses by suppressing charge recombination. and may act as buffer/protective layers and nanomorphology regulators for the absorber layer. One such interface is formed by the hole transport layer (HTL) and the organic/perovskite absorber. These HTLs typically consist of organic semiconductors, which, although are solution processable at low temperatures and allow perfect energy‐level alignment with the absorber layer and therefore efficient charge collection, are prone to degradation in ambient conditions and under continuous light exposure. In a quest for robust alternatives, inorganic materials such as metal oxides, graphene oxide, bronzes, copper thiocyanate, and transition metal dichalcogenides are actively investigated. However, their hole extraction capability is inferior compared with organic semiconductors as they possess specific energetics leading to significant charge extraction barriers and moderate charge collection. To achieve further advancements in their hole transporting capabilities, strongly interconnecting knowledge of their synthesis, electronic properties, and device performance metrics is required.

Herein, a small amount of the ionic liquid methylammonium difluoroacetate is introduced to anchor the organic cations via hydrogen bonding and to enhance the Pb–O interaction in perovskite precursors for efficient and stable solar cells.

The instability of organic cations in lead halide perovskite materials is a major obstacle for the commercial breakthrough of perovskite photovoltaics due to desorption of organic cations during the thermal annealing and device operation. Herein, a novel strategy is reported to improve the performance and stability of organic halide perovskite solar cells containing organic cations by adding a small amount of the ionic liquid methylammonium difluoroacetate (MA⁺DFA⁻). Nuclear magnetic resonance and Fourier‐transform infrared spectroscopy measurements show that MA⁺DFA⁻ can anchor the organic cations via hydrogen bonding and enhance the Pb–O interaction in perovskite precursors, leading to the retardation of the perovskite crystallization and improved stability of the perovskite precursor solution. Dynamic light scattering and scanning electron microscopy verify the defect‐passivation effect of MA⁺DFA⁻ on the perovskite precursors and films. The passivated perovskite film shows superior photo carrier dynamics as investigated by time‐resolved photoluminescence and transient absorption spectra. Moreover, the hydrogen bonding of the perovskite with MA⁺DFA⁻ imparts excellent ambient and thermal stability to the film as revealed by X‐ray diffraction measurements. As a result, devices with a high efficiency of 21.46% and excellent stability over 180 days in nitrogen atmosphere at room temperature are achieved with the ionic liquid.

The “double dipole step” model is used to explain the physicochemical property of the indium tin oxide (ITO)/polyvinylpyrrolidone (PVP) interface that the W _F reduction is caused by the directional intrinsic molecular dipole moments and the image dipole moments. Moreover, high‐performance inverted organic solar cells (OSCs) are achieved by introducing a self‐assembled ultrathin PVP layer using a simple immersion method.

Polyvinylpyrrolidone (PVP) has been successfully used as the cathode interfacial layer (CIL) in organic solar cells (OSCs) for work function (W _F) modification. However, detailed insight into the effect of a PVP interlayer on the physicochemical properties of the indium tin oxide (ITO) electrode in inverted OSCs (I‐OSCs) is still largely absent. Herein, the ITO/PVP interface is investigated by photoelectron spectroscopy and the mechanisms for the energy level alignment of PVP on different substrates in general are unraveled. The results indicate that the dipole formation that reduces the W _F is driven by not only the directional intrinsic molecular dipole moments associated with the γ‐lactam of PVP, but also an additional dipole step with the same direction created by the image charges in the contacting (semi‐)conductor layer. In addition, high‐performance inverted OSCs (I‐OSCs) are achieved by introducing a self‐assembled ultrathin PVP layer using a simple immersion method. This work provides enhanced understanding of the PVP‐based CIL and demonstrates its great potential in I‐OSC fabrication, which can pave the way to simplified manufacturing of low‐cost and large‐area devices in organic electronic technologies.

An unassisted overall solar‐to‐hydrogen efficiency of 8.54% is achieved on a monolithic integration of perovskite solar cells with low‐cost earth‐abundant co‐catalysts. The effective encapsulation of the perovskite solar cells and engineering of the co‐catalysts interfaces result in robust monolithic photoelectrodes, demonstrating continuous stable operation over 13 h. The excellent stability and good performance demonstrate the potential for efficient direct solar H₂ production.

Abstract

Metal halide perovskite solar cells have an appropriate bandgap (1.5–1.6 eV), and thus output voltage (>1 V), to directly drive solar water splitting. Despite significant progress, their moisture sensitivity still hampers their application for integrated monolithic devices. Furthermore, the prevalence of the use of noble metals as co‐catalysts for existing perovskite‐based devices undermines their use for low‐cost H₂ production. Here, a monolithic architecture for stable perovskite‐based devices with earth‐abundant co‐catalysts is reported, demonstrating an unassisted overall solar‐to‐hydrogen efficiency of 8.54%. The device layout consists of two monolithically encapsulated perovskite (FA_0.80MA_0.15Cs_0.05PbI_2.55Br_0.45) solar cells with low‐cost earth‐abundant CoP and FeNi(OH) _x co‐catalysts as the photocathode and photoanode, respectively. The CoP‐based photocathode demonstrates more than 17 h of continuous operation, with a photocurrent density of 12.4 mA cm⁻² at 0 V and an onset potential as positive as ≈1 V versus reversible hydrogen electrode (RHE). The FeNi(OH) _x ‐based photoanode achieves a photocurrent of 11 mA cm⁻² at 1.23 V versus RHE for more than 13 h continuous operation. These excellent stability and performance demonstrate the potential for monolithic integration of perovskite solar cells and low‐cost earth‐abundant co‐catalysts for efficient direct solar H₂ production.

SnO₂ has been applied as an efficient electron transport layer for perovskite solar cells over the past few years. In this progress report, recent advances in SnO₂ modification toward high efficiency and stability are summarized from the perspective of the optimization strategies, and the remaining challenges as well as opportunities for future research are also discussed.

Abstract

The electron transport layer plays a key role in affecting the charge dynamics and photovoltaic parameters in perovskite solar cells. Compared to other counterparts, SnO₂ has unique advantages such as low temperature fabrication and high electron extraction ability, and it receives extra attentions from the research community since the first report. Planar‐type perovskite solar cells based on SnO₂ exhibit a simple architecture and state of art device can achieve a power conversion efficiency of over 23%, which can compete with traditional devices using mesoporous TiO₂. The modification engineering of SnO₂ has contributed significantly to the enhanced device performance during the past years. There is still great potential for further improvement in the efficiency and long‐term stability. Herein recent advances toward modifying the optoelectronic properties of SnO₂ from the perspective of the optimization strategies are summarized and the remaining challenges as well as opportunities for future research are discussed. The continuous efforts dedicated to this exciting field may pave the way for developing commercial perovskite solar cells.

This review summarizes the isomerization strategy of nonfullerene small‐molecule acceptors for organic solar cells, and discusses the key structure–property relationships in depth.

Abstract

Nonfullerene acceptors (NFAs) are a current focus of research on bulk‐heterojunction organic solar cells (OSCs), as they can exhibit strong absorption, suitably matched energy levels, and good stability. Isomerization affords a new material design strategy for nonfullerene small‐molecule acceptors (SMAs). In this article, the development of isomeric nonfullerene SMAs, including isomeric perylene diimide (PDI)‐based nonfullerene SMAs and isomeric acceptor–donor–acceptor (A–D–A)‐type nonfullerene SMAs, is reviewed. The general design principles for isomeric SMAs and the key structure–property relationships are comprehensively surveyed and discussed. The remaining challenges and promising future directions of isomeric nonfullerene acceptors are presented.

The novel use of cheap copper‐based corrole as hole transporting material in perovskite solar cells is shown by improving the device thermal stability of n–i–p mesoscopic architecture under prolonged 85 °C stress conditions. Corrole‐based devices show a remarkable power conversion efficiency above 16% by retaining more than 65% of the initial power conversion efficiency after 1000 h of thermal stress.

Abstract

Perovskite solar cells (PSCs) represent nowadays a promising starting point to develop a new efficient and low‐cost photovoltaic technology due to the demonstrated power conversion efficiency (PCE) exceeding 25% on small area devices. However, best reported devices suffer from stability issue under real working conditions thus slowing down the race for the commercialization. In particular, the hole transporting material commonly employed in mesoscopic n–i–p PSCs (nip‐mPSCs), namely spiro‐OMeTAD, is strongly corrupted when subjected to temperatures above 70 °C due to intrinsic thermal instability and because of the dopant employed to improve the hole mobility. In this work, the novel use of a copper‐based corrole as HTM is proposed to improve the device thermal stability of nip‐mPSCs under prolonged 85 °C stress conditions. Corrole‐based devices show remarkable PCE above 16% by retaining more than 65% of the initial PCE after 1000 h of thermal stress, while spiro‐OMeTAD cells abruptly lose more than 60% after the first 40 h. Once scaled‐up to large area modules, the proposed device structure can truly represent a possible way to pass thermal stress tests proposed by IEC‐61646 standards and, not less importantly, the high temperature required by the lamination process for panel production.

A clear solid‐state aggregation transition of the acceptor N3 is discovered, which enables a double‐annealing method that can fine‐tune aggregation and morphology. Compared with the 16.6% efficiency for PM6:N3:PC₇₁BM‐control devices, a higher efficiency of 17.6% is obtained through the improved protocol. The results provide a molecular design and engineering conundrum to achieve simultaneously low annealing temperatures, high efficiency, and stability.

Abstract

Thermal transition of organic solar cells (OSCs) constituent materials are often insufficiently researched, resulting in trial‐and‐error rather than rational approaches to annealing strategies to improve domain purity to enhance the power conversion efficiency. Despite the potential utility, little is known about the thermal transitions of the modern high‐performance acceptors Y6 and N3. Here, by using an optical method, it is discovered that the acceptor N3 has a clear solid‐state aggregation transition at 82 °C. This unusually low transition not only explains prior optimization protocols, but the transition informs and enables a double‐annealing method that can fine‐tune aggregation and the device morphology. Compared with 16.6% efficiency for PM6:N3:PC₇₁BM control devices, higher efficiency of 17.6% is obtained through the improved protocol. Morphology characterization with x‐ray scattering methods reveals the formation of a multilength scale morphology. Moreover, the double‐annealing method is illustrated and easily transferred and validated with Y6‐based devices, using the transition of Y6 at 102 °C. As a result, the PCE improved from 16.0% to 16.8%. Design of high‐performance acceptors with yet lower aggregation transitions might be required for OSCs to successfully transition to low thermal budget industrial processing methods where annealing temperatures on plastic substrates have to be kept low.

Molecular packing and thermodynamic properties of D18‐based fullerene‐free organic solar cells are studied. The D18 polymer exhibits strong chain extension in films, which is beneficial to charge transport. Miscibility and other characterizations explain the disparate performance of three systems and the processing procedures.

Abstract

Organic solar cells (OSCs) based on D18:Y6 have recently exhibited a record power conversion efficiency of over 18%. The initial work is extended and the device performance of D18‐based OSCs is compared with three non‐fullerene acceptors, Y6, IT‐4F, and IEICO‐4Cl, and their molecular packing characteristics and miscibility are studied. The D18 polymer shows unusually strong chain extension and excellent backbone ordering in all films, which likely contributes to the excellent hole‐transporting properties. Thermodynamic characterization indicates a room‐temperature miscibility for D18:Y6 and D18:IT‐4F near the percolation threshold. This corresponds to an ideal quench depth and explains the use of solvent vapor annealing rather than thermal annealing. In contrast, D18:IEICO‐4Cl is a low‐miscibility system with a deep quench depth during casting and poor morphology control and low performance. A failure of ternary blends with PC₇₁BM is likely due to the near‐ideal miscibility of Y6 to begin with and indicates that strategies for developing successful ternary or quaternary solar cells are likely very different for D18 than for other high‐performing donors. This work reveals several unique property–performance relations of D18‐based photovoltaic devices and helps guide design or fabrication of yet higher efficiency OSCs.

9‐Fluorenone‐1‐carboxylic acid (FCA) is utilized to prolong the lifetime of photogenerated excitons in a nonfullerene acceptor (IT‐M) approximately twofold, ensuring longer exciton diffusion length and efficiency enhancement in organic photovoltaic devices. The prolongation arises from the discovered intermolecular vibrational coupling between the electronic excited state of IT‐M and the electronic ground state of FCA, thus suppressing the nonradiative decay.

Abstract

Exciton lifetime (τ) is crucial for the migration of excitons to donor/acceptor interfaces for subsequent charge separation in organic solar cells (OSCs); however, obvious prolongation of τ has rarely been achieved. Here, by introducing a solid additive 9‐fluorenone‐1‐carboxylic acid (FCA) into the active layer, which comprises a nonfullerene acceptor, 3,9‐bis(2‐methylene‐((3‐(1,1‐dicyanomethylene)‐6/7‐methyl)‐indanone))‐5,5,11,11‐tetrakis(4‐hexylphenyl)‐dithieno[2,3‐d:2′,3′‐d′]‐s‐indaceno[1,2‐b:5,6‐b′]dithiophene (IT‐M), τ is substantially prolonged from 491 to 928 ps, together with obvious increases in fluorescence intensity and quantum yield. Time‐resolved transient infrared spectra indicate the presence of an intermolecular vibrational coupling between the electronic excited state of IT‐M and the electronic ground state of FCA, which is first observed here and which can suppress the internal conversion process. IT‐M‐based OSCs display an improved short‐circuit current and fill factor after the addition of FCA. Thus, the power conversion efficiency is increased, particularly for devices with a large donor/acceptor ratio of 1:4, whose efficiency is increased by 56%. This study describes a novel method, which is also applicable to other nonfullerene acceptors, for further improving the performance of OSCs without affecting their morphology and light absorption properties.

The fabrication challenges of monolithic all‐perovskite tandem photovoltaics are detailed in a step‐by‐step, choose‐your‐own‐adventure fashion. The trade‐offs between sub‐cell efficiency and processing stability are highlighted and pros and cons are weighed. Through this detailed analysis, a few routes to reach >30% power conversion efficiency and the necessary work are identified.

Abstract

Metal halide perovskites (MHPs) have transfixed the photovoltaic (PV) community due to their outstanding and tunable optoelectronic properties coupled to demonstrations of high‐power conversion efficiencies (PCE) at a range of bandgaps. This has motivated the field to push perovskites to reach the highest possible performance. One way to increase the efficiency is by fabricating multijunction solar cells, which can split the solar spectrum, reducing thermalization loss. Low‐cost all‐perovskite tandems have a real chance to soon exceed 30% PCE, which could transform the PV industry. Achieving this goal requires the identification of perovskite sub‐cells that are both highly efficient and can be effectively integrated. Herein, it is discussed how to navigate the multiple‐choice adventure in choosing between the myriad of options and considerations present when deciding what perovskite materials, contact layers, and processing tools to use. Some of the potential fabrication pitfalls often encountered in MHP based tandem PVs are highlighted, so that they can hopefully be avoided in the future.

Organic solar cells have the potential to become the cheapest form of electricity, even beating silicon solar cells, at least in principle. This article summarizes where the field is on its way towards successful large‐scale commercialization, highlighting research challenges, discussing the status of current and future applications as well as the environmental footprint of this renewable energy technology.

Abstract

Organic solar cells have the potential to become the cheapest form of electricity, beating even silicon photovoltaics. This article summarizes the state of the art in the field, highlighting research challenges, mainly the need for an efficiency increase as well as an improvement in long‐term stability. It discusses possible current and future applications, such as building integrated photovoltaics or portable electronics. Finally, the environmental footprint of this renewable energy technology is evaluated, highlighting the potential to be the energy generation technology with the lowest carbon footprint of all.

An additive‐involved leaching method is proposed to reduce the preparation temperature of CsPbI₃ to 100 °C. The CsPbI₃ perovskite film with high crystallinity is formed by an ion exchange reaction between DMAPbI₃ and Cs₄PbI₆. More than 16% photoelectric conversion efficiency can be achieved and the inencapsulation device exhibits remaekable stability.

Abstract

Inorganic CsPbI₃ perovskite with an optical bandgap ranging from 1.67 to 1.75 eV is a promising light‐harvesting material as a top cell in tandem solar cells, but its high fabrication temperature can damage the middle layers or the bottom subcells. Here, an additive‐involved leaching method to fabricate CsPbI₃ perovskite films is demonstrated, which can decrease the preparation temperature to 100 °C. The CsPbI₃ perovskite films with high crystallinity are achieved by a solution assisted reaction between DMAPbI₃ and Cs₄PbI₆ with the leaching of DMA⁺, Cs⁺, and I⁻. The as‐prepared CsPbI₃ perovskite films exhibit much superior stability compared to their high‐temperature counterparts. As a result, a power conversion efficiency of over 16% is obtained, and the unencapsulated device maintains over 93% of the initial efficiency after aging for 30 days in air with a relative humidity of 10%.

A combination of in‐ and ex situ measurements are used to monitor the degradation processes in mixed‐halide perovskite light‐emitting devices. Device performance degradation is found to arise from accumulation of bromide at the interface between the perovskite and electron injecting layer, causing nonradiative recombination. Potassium halides mitigate the ionic movement and degradation, leading to better stability of devices under operation.

Abstract

Halide perovskites have attracted substantial interest for their potential as disruptive display and lighting technologies. However, perovskite light‐emitting diodes (PeLEDs) are still hindered by poor operational stability. A fundamental understanding of the degradation processes is lacking but will be key to mitigating these pathways. Here, a combination of in operando and ex situ measurements to monitor the performance degradation of (Cs_0.06FA_0.79MA_0.15)Pb(I_0.85Br_0.15)₃ PeLEDs over time is used. Through device, nanoscale cross‐sectional chemical mapping, and optical spectroscopy measurements, it is revealed that the degraded performance arises from an irreversible accumulation of bromide content at one interface, which leads to barriers to injection of charge carriers and thus increased nonradiative recombination. This ionic segregation is impeded by passivating the perovskite films with potassium halides, which immobilizes the excess halide species. The passivated PeLEDs show enhanced external quantum efficiency (EQE) from 0.5% to 4.5% and, importantly, show significantly enhanced stability, with minimal performance roll‐off even at high current densities (>200 mA cm⁻²). The decay half‐life for the devices under continuous operation at peak EQE increases from <1 to ≈15 h through passivation, and ≈200 h under pulsed operation. The results provide generalized insight into degradation pathways in PeLEDs and highlight routes to overcome these challenges.

A rerouting crystallization pathway (RCP) is developed to suppress defects in vertically oriented 2D perovskites. Lower trap states, better homogeneity, and higher charge transport/collection efficiency are obtained due to the improved film quality. Solar cells using these RCP‐2D perovskite films show a highest efficiency of 18.5% with a high fill factor of 83.4% and exhibit superior environmental stability.

Abstract

Vertically oriented 2D perovskites exhibit promising optoelectronic properties and intrinsic stability, but their photovoltaic application is still limited by the low power conversion efficiency (PCE) compared to 3D analogs. Here, a new crystallization pathway (RCP) is reported to suppress defects in vertically oriented 2D perovskite caused by its over‐rapid self‐assembly behavior. By controlling the specific adsorption of an ammonium halide additive on different perovskite crystal planes, the dynamic preferred growth of (111) plane is intentionally restrained, and the minority (202) planes emerge as secondary nucleation sites to stimulate the creation of large grains. As the halogen‐regulated deprotonation of ammonium proceeds, the (111) crystal plane gradually recovers its growth dominance, and a vertically oriented 2D perovskite film finally forms with high homogeneity, reduced trap density of states, and desired carrier transport/collection kinetics. Solar cells using RCP‐2D films show a highly reproducible and stable PCE reaching 18.5% with a high fill factor of 83.4%. These findings provide critical missing information on simultaneously achieving highly oriented and less defective 2D perovskite films for excellent device performance.

To fine‐tune the energy levels of polymer donors, a family of random polymers is synthesized, which shows favorable properties of aggregation and morphology. The performance of these polymers is less sensitive to their molecular weights compared with PM7. Thus, multiple cases of highly efficient nonfullerene organic solar cells are achieved with efficiencies between 16.0% and 17.1%.

Abstract

Developing high‐performance donor polymers is important for nonfullerene organic solar cells (NF‐OSCs), as state‐of‐the‐art nonfullerene acceptors can only perform well if they are coupled with a matching donor with suitable energy levels. However, there are very limited choices of donor polymers for NF‐OSCs, and the most commonly used ones are polymers named PM6 and PM7, which suffer from several problems. First, the performance of these polymers (particularly PM7) relies on precise control of their molecular weights. Also, their optimal morphology is extremely sensitive to any structural modification. In this work, a family of donor polymers is developed based on a random polymerization strategy. These polymers can achieve well‐controlled morphology and high‐performance with a variety of chemical structures and molecular weights. The polymer donors are D–A1–D–A2‐type random copolymers in which the D and A1 units are monomers originating from PM6 or PM7, while the A2 unit comprises an electron‐deficient core flanked by two thiophene rings with branched alkyl chains. Consequently, multiple cases of highly efficient NF‐OSCs are achieved with efficiencies between 16.0% and 17.1%. As the electron‐deficient cores can be changed to many other structural units, the strategy can easily expand the choices of high‐performance donor polymers for NF‐OSCs.

Highly efficient all‐inorganic perovskite solar cells based on CsPbI _x Br_{3‐ x} are fabricated through the introduction of a spontaneous interfacial manipulation method. A spontaneously formed ultrathin 2D perovskite top interface can not only eliminate interfacial defects but also effectively prevent moisture penetration. As a result, the device exhibits a power conversion efficiency of 18% with extended device stability.

Abstract

Cesium‐based all‐inorganic halide perovskites solar cells (PSCs) have recently attracted increasing attention. Currently, due to the existence of high defects density and unoptimized interfacial morphology, “state‐of‐the‐art” performances of all‐inorganic PSCs are still far away from their theoretical limits. Although commonly used two‐step passivation methods can effectively passivate the perovskite surface, they will inevitably detriment the original perovskite morphology due to the use of weak‐polarity solvents. This will potentially result in the unintentional doping, uncontrollable interfacial band alignment, and the additional defects formation. Hence, a spontaneous interfacial manipulation (SIM) method is developed to self‐organize a 2D/3D multidimensional perovskite top interface. It is demonstrated that the spontaneously formed ultrathin 2D perovskite can not only eliminate the interfacial defects, but also effectively prevent moisture penetration. As a result, a significant power conversion efficiency enhancement from 13.64% to over 18% is obtained along with greatly extended device lifetime, for CsPbI _x Br_{3‐ x} ‐based all‐inorganic PSC.