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High‐quality and all‐inorganic CsPbI₂Br perovskite film with lower defects and improved hydrophobicity is prepared via a facile additive engineering with trace S₈, resulting in inverted solar cells with improved efficiency and stability.

Though prized for excellent thermal stability, inorganic perovskites are still behind organic/inorganic hybrid perovskites due to their high‐density defects and poor hydrophobicity. Herein, trace hydrophobic S₈ is used as additive to optimize the solution‐processed CsPbI₂Br perovskite film. A series of characterizations reveal that S₈ additive not only leads to retarded crystallization of α‐CsPbI₂Br perovskite at low temperature (<150 °C) via self‐formed Pb(S₈) _x ²⁺ intermediate but also induces efficient grain‐boundary passivation via distinctive PbS coordination interaction and reduced wettability on perovskite surface, which all point to the formation of the perovskite film with reduced defects and improved hydrophobicity. As a result, the inverted perovskite solar cells (PSCs) based on the optimized all‐inorganic perovskite of CsPbI₂Br:S₈ deliver an increased power conversion efficiency (PCE) from 12.76% to 14.46% as well as remarkably enhanced device stability under thermal or ambient condition. This work thus provides a simple way as well as new insights for boosting the performance of solution‐processed all‐inorganic perovskite.

A power conversion efficiency (PCE) of 17.59% is achieved in ternary organic photovoltaic cells (OPVs) with BTP‐BO‐4F:Y6‐1O as alloyed acceptor, resulting from the simultaneously improved three photovoltaic parameters. The good compatibility of used materials is one of the prerequisites for achieving efficient ternary OPVs.

Efficient organic photovoltaic cells (OPVs) are fabricated using two structurally similar Y6 derivations (BTP‐BO‐4F and Y6‐1O) as acceptor and PM6 as donor. The two binary OPVs exhibit a high fill factor (FF) (>76%), the complementary short‐circuit‐current density (J _SC) and open‐circuit voltage (V _OC). The high FFs of binary OPVs indicate the good compatibility of corresponding materials to form efficient charge transport channels. A power conversion efficiency (PCE) of 17.59% is obtained from ternary OPVs with 15 wt% Y6‐1O in acceptors, benefiting from the simultaneously improved J _SC of 26.13 mA cm⁻², a V _OC of 0.860 V, and an FF of 78.26%. The values of V _OC of ternary OPVs can be gradually increased along with the incorporation of Y6‐1O, suggesting the preferred formation of an alloyed state between BTP‐BO‐4F and Y6‐1O due to their good compatibility. Meanwhile, the cascaded energy levels of BTP‐BO‐4F and Y6‐1O can form efficient electron transport channels in ternary active layers. The main contribution of Y6‐1O can be summarized as enhancing photon harvesting, optimizing phase separation, and adjusting molecular arrangement. The experimental results may provide new insight on developing efficient ternary OPVs by selecting two well‐compatible acceptors.

Self‐assembled P3HT‐COOH is an excellent hole extraction layer to fabricate robust, high‐performance, and extremely reproducible perovskite solar cells. The well‐aligned self‐assembled P3HT‐COOH generates a dipole layer between indium tin oxide and perovskite, substantially retarding interface charge recombination and producing highly sensitive devices to dim light. The enhanced crystallinity and preferred out‐of‐plane orientation play a key role to suppress the device degradation process.

Abstract

Crystallinity and crystal orientation have a predominant impact on a materials’ semiconducting properties, thus it is essential to manipulate the microstructure arrangements for desired semiconducting device performance. Here, ultra‐uniform hole‐transporting material (HTM) by self‐assembling COOH‐functionalized P3HT (P3HT‐COOH) is fabricated, on which near single crystal quality perovskite thin film can be grown. In particular, the self‐assembly approach facilitates the P3HT‐COOH molecules to form an ordered and homogeneous monolayer on top of the indium tin oxide (ITO) electrode facilitate the perovskite crystalline film growth with high quality and preferred orientations. After detailed spectroscopy and device characterizations, it is found that the carboxylic acid anchoring groups can down‐shift the work function and passivate the ITO surface, retarding the interface carrier recombination. As a result, the device made with the self‐assembled HTM show high open‐circuit voltage over 1.10 V and extend the lifetime over 4,300 h when storing at 30% relative humidity. Moreover, the cell works efficiently under much reduced light power, making it useful as power source under dim‐light conditions. The demonstration suggests a new facile way of fabricating monolayer HTM for high efficiency perovskite devices, as well as the interconnecting layer needed for tandem cell.

In this work, a perovskite solar cell (PSC) is fabricated via a scalable solution process under ambient conditions. A hysteresis‐free, high‐efficiency (21.1%), laminar‐air‐knife‐assisted meniscus coating of PSCs is demonstrated at room temperature and a relative humidity of 55%. An in‐depth in situ investigation by time‐resolved UV–vis spectroscopy is conduced to explore the nucleation dynamics.

Abstract

Extensive studies are conducted on perovskite solar cells (PSCs) with significant performance advances (mainly spin coating techniques), which have encouraged recent efforts on scalable coating techniques for the manufacture of PSCs. However, devices fabricated by blade coating techniques are inferior to state‐of‐the‐art spin‐coated devices because the power conversion efficiency (PCE) is highly dependent on the morphology and crystallization kinetics in the controlled environment and the delicate solvent system engineering. In this study, based on the widely studied perovskite solution system dimethylformamide–dimethyl sulfoxide, air‐knife‐assisted ambient fabrication of PSCs at a high relative humidity of 55 ± 5% is reported. In‐depth time‐resolved UV–vis spectrometry is carried out to investigate the impact of solvent removal and crystallization rate, which are critical factors influencing the crystallization kinetics and morphology because of adventitious moisture. UV–vis spectrometry enables accurate determination of the thickness of the wet precursor film. Anti‐solvent‐free, high‐humidity ambient coatings of hysteresis‐free PSCs with PCEs of 21.1% and 18.0% are demonstrated for 0.06 and 1 cm² devices, respectively. These PSCs exhibit comparable stability to those fabricated in a glovebox, thus demonstrating their high potential.

A dual‐functional method of simultaneously passivating trap defects in both perovskite and electron transport layer (ETL) films is proposed. Europium ions distribute throughout SnO₂ film and diffuse into perovskite, while most of Eu³⁺ remain at the interface. Under the synergistic effect of distributed Eu³⁺, the electron mobility of ETL is improved and the trap density of perovskite is also reduced.

Abstract

So far, most techniques for modifying perovskite solar cells (PSCs) focus on either the perovskite or electron transport layer (ETL). For the sake of comprehensively improving device performance, a dual‐functional method of simultaneously passivating trap defects in both the perovskite and ETL films is proposed that utilizes guidable transfer of Eu³⁺ in SnO₂ to perovskite. Europium ions are distributed throughout the SnO₂ film during the formation process of SnO₂, and they can diffuse directionally through the SnO₂/perovskite interface into the perovskite, while most of the europium ions remain at the interface. Under the synergistic effect of distributed Eu³⁺ in the SnO₂ and aggregated Eu³⁺ at the interface, the electron mobilities of ETLs are evidently improved. Meanwhile, diffused Eu³⁺ ions passivate the perovskite to reduce trap densities at the grain boundaries, which can dramatically elevate the open‐circuit voltage (V _oc) of PSCs. Finally, the mainly PSCs coated on SnO₂:Eu³⁺ ETL achieve a power conversion efficiency of 20.14%. Moreover, an unsealed device degrades by only 13% after exposure to ambient atmosphere for 84 days.

A dissymmetric fused‐ring acceptor BTIC‐2Cl‐γCF₃ with chlorine and trifluoromethyl end groups give a power conversion efficiency (PCE) of over 17 % which is the highest among polymer solar cells processed by halogen‐free solvents. Dissymmetric chlorination and trifluoromethylation is a practical approach towards a low band‐gap acceptor for eco‐compatible processed photovoltaic applications.

Abstract

To elevate the performance of polymer solar cells (PSC) processed by non‐halogenated solvents, a dissymmetric fused‐ring acceptor BTIC‐2Cl‐γCF₃ with chlorine and trifluoromethyl end groups has been designed and synthesized. X‐ray crystallographic data suggests that BTIC‐2Cl‐γCF₃ has a 3D network packing structure as a result of H‐ and J‐aggregations between adjacent molecules, which will strengthen its charge transport as an acceptor material. When PBDB‐TF was used as a donor, the toluene‐processed binary device realized a high power conversion efficiency (PCE) of 16.31 %, which improved to 17.12 % when PC71ThBM was added as the third component. Its efficiency of over 17 % is currently the highest among polymer solar cells processed by non‐halogenated solvents. Compared to its symmetric counterparts BTIC‐4Cl and BTIC‐CF₃‐γ, the dissymmetric BTIC‐2Cl‐γCF₃ integrates their merits, and has optimized the molecular aggregations with excellent storage and photo‐stability, and also extending the maximum absorption peak in film to 852 nm. The devices exhibit good transparency indicating a potential utilization in semi‐transparent building integrated photovoltaics (ST‐BIPV).

High performance perovskite solar modules (PSMs) are fabricated by introducing NH₄Cl to induce the formation of the intermediate phases. The PSMs show long‐term operational stability with a T ₈₀ lifetime under continuous light illumination exceeding 1600 h for a 5 × 5 cm² solar module and 1100 h for a 10 × 10 cm² solar module.

Abstract

In addition to high efficiencies, upscaling and long‐term operational stability are key pre‐requisites for moving perovskite solar cells toward commercial applications. In this work, a strategy to fabricate large‐area uniform and dense perovskite films with a thickness over one‐micrometer via a two‐step coating process by introducing NH₄Cl as an additive in the PbI₂ precursor solution is developed. Incorporation of NH₄Cl induces the formation of the intermediate phases of x[NH₄ ⁺]·[PbI₂Cl _x ] ^{x −} and HPbI_{3− x} Cl _x , which can effectively retard the crystallization rate of perovskite leading to uniform and compact full‐coverage perovskite layers across large areas with high crystallinity, large grain sizes, and small surface roughness. The 5 × 5 and 10 × 10 cm² perovskite solar modules (PSMs) based on this method achieve a power conversion efficiency (PCE) of 14.55% and 10.25%, respectively. These PSMs also exhibit good operational stability with a T ₈₀ lifetime (the time during which the solar module PCE drops to 80% of its initial value) under continuous light illumination exceeding 1600 h (5 × 5 cm²) and 1100 h (10 × 10 cm²), respectively.

Organic photovoltaics have long promised low embodied energy, low cost solar power but have yet to make the commercial transition. Recent advances in efficiencies are potentially about to change this status‐quo, driven by a new class of semiconductors called the non‐fullerene electron acceptors. The emergence of these materials is reviewed, and perspectives provided as to future challenges and performance.

Abstract

Organic solar cells are composed of electron donating and accepting organic semiconductors. Whilst a significant palette of donors has been developed over three decades, until recently only a small number of acceptors have proven capable of delivering high power conversion efficiencies. In particular the fullerenes have dominated the landscape. In this perspective, the emergence of a family of materials–the non‐fullerene acceptors (NFAs) is described. These have delivered a discontinuous advance in cell efficiencies, with the significant milestone of 20% now in sight. Intensive international efforts in synthetic chemistry have established clear design rules for molecular engineering enabling an ever‐expanding number of high efficiency candidates. However, these materials challenge the accepted wisdom of how organic solar cells work and force new thinking in areas such as morphology, charge generation and recombination. This perspective provides a historical context for the development of NFAs, and also addresses current thinking in these areas plus considers important manufacturability criteria. There is no doubt that the NFAs have propelled organic solar cell technology to the efficiencies necessary for a viable commercial technology–but how far can they be pushed, and will they also deliver on equally important metrics such as stability?

Organic solar cells (OSCs) outperform other technologies at low‐light intensities providing an exciting opportunity for commercialization. Previous OSC low‐light studies utilize non‐scalable materials or methods unsuitable for commercialization. Scalable materials are used to highlight the current performance of commercially relevant low‐light OSCs. The effect of parasitic resistance and a light‐soaking effect that is critical for low‐light performance are also investigated.

Abstract

Low‐light applications provide an exciting market opportunity for organic solar cells (OSCs). However, so far, studies have only considered OSCs of limited commercial viability. Herein, the applicability of a fully‐scalable, flexible, inverted non‐fullerene acceptor (NFA) containing OSC is demonstrated by showing its superior performance to silicon under low‐light, achieving 40 µW cm⁻² maximum power output at 1300 lx illumination. The effect of parasitic resistance and dark current on low‐light performance are identified. Furthermore, an atmosphere sensitive light‐soaking (LS) effect, critical for low‐light performance and resulting in undesirable S‐shaped current‐voltage characteristics, is analyzed. By employing different interlayers and photoactive layers (PALs) the origin of this LS effect is identified as poor electron extraction at the electron transport layer (ETL)/PAL interface when the common ETL ZnO is used. Two strategies are implemented to overcome the LS effect: replacement of ZnO with SnO₂ nanoparticles to reduce ETL sub‐gap electron trap states or tuning the NFA energy levels to optimize interfacial energetics. Finally, the commercial viability of these LS‐free devices is demonstrated by fabricating fully printed large‐area modules (21.6 cm²) achieving a maximum power output of 17.2 µW cm⁻², providing the most relevant example of the currently obtainable performance in commercial low‐light OSCs.

It is critical to understand how metal halide perovskite solar cells behave under reverse bias. Herein, it is shown that the power conversion efficiency losses after prolonged reverse bias are due to accumulation of holes within the bulk perovskite. Consequently, determinantal electrochemical oxidation reactions occur in the bulk, resulting in increased recombination and halide/halogen diffusion into charge transport layers.

Abstract

Partial shading of a solar module can induce a set of cells within the module to operate under reverse bias. Studies have shown that metal halide perovskite solar cells with a wide variety of compositions and contacts exhibit interesting behavior in reverse bias that includes both reversible performance loss and non‐reversible degradation. In this paper, an advanced drift‐diffusion approach incorporating an electrochemical term to explain the short‐circuit, open circuit and fill factor losses that are experimentally measured after prolonged reverse bias is used. It is shown that holes can tunnel into the perovskite due to sharp band bending near the contact, accumulate within the bulk of the perovskite absorber, and trigger the oxidation of halides to form neutral halogens. The density of neutral halogens is much higher in reverse bias because there are hardly any electrons available to reduce the iodine. The resulting halogens act as bulk recombination centers. While the interstitial halogen density does decay when the cell is operated in forward bias, permanent degradation can occur if the iodine diffuses out of the perovskite layer. Finally, the ways in which changing parameters such as the mobile ion density or the series resistance at the contact can influence device performance and stability are discussed.

Conformation effects of Y6‐type acceptors are systematically studied based on asymmetric design strategies. Z‐shape and W‐shape conformations‐based acceptors can help reduce energy loss in devices through significantly suppressed nonradiative energy loss. Benefiting from the high open‐circuit voltage of BP5T‐4F in the devices, ternary organic solar cells based on PM6:BP5T‐4F:CH1007 achieve a 17.2% efficiency.

Abstract

Y6, as a state‐of‐the‐art nonfullerene acceptor (NFA), is extensively optimized by modifying its side chains and terminal groups. However, the conformation effects on molecular properties and photovoltaic performance of Y6 and its derivatives have not yet been systematically studied. Herein, three Y6 analogs, namely, BP4T‐4F, BP5T‐4F, and ABP4T‐4F, are designed and synthesized. Owing to the asymmetric molecular design strategies, three representative molecular conformations for Y6‐type NFAs are obtained through regulating the lateral thiophene orientation of the fused core. It is found that conformation adjustment imposes comprehensive effects on the molecular properties in neat and blend films of these NFAs. As a result, organic solar cells (OSCs) fabricated with PM6:BP4T‐4F, PM6:BP5T‐4F, and PM6:ABP4T‐4F show high power conversion efficiency of 17.1%, 16.7%, and 15.2%, respectively. Interestingly, these NFAs with different conformations also show reduced energy loss (E _loss) in devices via gradually suppressed nonradiative E _loss. Moreover, by employing a selenium‐containing analog, CH1007, as the complementary third component, ternary OSCs based on PM6:BP5T‐4F:CH1007 (1:1.02:0.18) achieve a 17.2% efficiency. This work helps shed light on engineering the molecular conformation of NFAs to achieve high efficiency OSCs with reduced voltage loss.

High‐performance organic semi‐transparent photovoltaic (ST‐OPV) devices are achieved by improving the light‐absorbing selectivity, that is, the light‐absorbing capability in invisible regions and light transmission in the visible region. Systematic optimization, including developing a numerical method for photo‐active layer screening, interface engineering, and optical manipulation, enables high‐performance ST‐OPVs with the best light utilization efficiency of 4.1%, ranking among the highest for ST‐OPVs.

Abstract

Semi‐transparent organic photovoltaics (ST‐OPVs) are promising solar windows for building integration. Improving the light‐absorbing selectivity, that is, transmitting the visible photons while absorbing the invisible ones, is a key step toward high‐performance ST‐OPV. To achieve this goal, the optical properties of the active layer, transparent electrode, and capping layer are comprehensively tailored, and a highly efficient ST‐OPV with good absorbing selectivity is demonstrated. First, a numerical method is established to quantify the absorbing selectivity of materials and devices, based on which, an infrared absorbing non‐fullerene acceptor, that is, H3, is selected among a large pool of photo‐active materials. Second, an ultra‐smooth transparent thin Ag layer with small granule size is developed via polyethylenimine wetting, which alleviates light scattering and improves the electric properties for ST‐OPV. Finally, as guided by optical simulation, a TeO₂ capping layer is deposited on top of the ultra‐thin Ag to further improve the light‐absorbing selectivity. As a result, the light utilization efficiency is significantly improved to 3.95 ± 0.02% (best ≈4.06%), with a good color rendering index of 76.85. These results make it one of the best among color‐neutral ST‐OPVs. This work stresses the importance of manipulating the light‐absorbing selectivity for high‐performance ST‐OPVs.

4‐Dimethylaminopyridine (DMAP) is introduced to develop a facile technique for selectively passivating grain boundaries (GB) and controlling the topographical boundary of perovskite surfaces near GBs. A power conversion efficiency of 22.4% is achieved for a planar perovskite solar cell with DMAP treatment and the device stability under damp‐heat and light irradiation is improved.

Abstract

Recent progress in highly efficient perovskite solar cells (PSCs) has been made by virtue of interfacial engineering on 3D perovskite surfaces for their defect control, however, the structural stability of the modified interface against external stimuli still remains unresolved. Herein, 4‐dimethylaminopyridine (DMAP) is introduced to develop a facile technique for selectively passivating the grain boundary (GB) and controlling the topographical boundary of the perovskite surface near the GB. Through the surface treatment of DMAP, strongly bound DMAP crystals are selectively formed at the GB, which serves two functions: nonradiative recombination at GB is effectively reduced by healing the uncoordinated Pb²⁺ while adhesion strength between the perovskite and the poly(triaryl amine) (PTAA) polymer is significantly enhanced by a mechanical interlock effect. A planar PSC with DMAP treatment exhibits a champion power conversion efficiency of 22.4%, which is not only much higher than the 20.04% observed for a nontreated control device, but also the highest among the planar PSCs using PTAA polymers as a hole transport material. Furthermore, the use of DMAP leads to a substantial improvement in the device stability under damp‐heat test and light irradiation.

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.

Nonfullerene acceptors dominate organic solar cell research due to their promising high device efficiencies. However, key challenges for achieving high stability in commercially viable devices still remain. In this review, recent progress and challenges toward stable organic solar cells are discussed correlating molecular design and device engineering to device stability.

Abstract

Organic solar cells (OSCs) based on nonfullerene acceptors (NFAs) have made significant breakthrough in their device performance, now achieving a power conversion efficiency of ≈18% for single junction devices, driven by the rapid development in their molecular design and device engineering in recent years. However, achieving long‐term stability remains a major challenge to overcome for their commercialization, due in large part to the current lack of understanding of their degradation mechanisms as well as the design rules for enhancing their stability. In this review, the recent progress in understanding the degradation mechanisms and enhancing the stability of high performance NFA‐based OSCs is a specific focus. First, an overview of the recent advances in the molecular design and device engineering of several classes of high performance NFA‐based OSCs for various targeted applications is provided, before presenting a critical review of the different degradation mechanisms identified through photochemical‐, photo‐, and morphological degradation pathways. Potential strategies to address these degradation mechanisms for further stability enhancement, from molecular design, interfacial engineering, and morphology control perspectives, are also discussed. Finally, an outlook is given highlighting the remaining key challenges toward achieving the long‐term stability of NFA‐OSCs.

Large‐area prepatterned silver nanowire electrodes are prepared via gravure printing, which show high uniformity and balanced conductivity (10.8 Ω sq⁻¹) and transparency (95.4%). High power conversion efficiencies of 15.28% and 13.61% are achieved for 0.04 and 1 cm² cells, respectively.

Abstract

With the aim of developing high‐performance flexible polymer solar cells, the preparation of flexible transparent electrodes (FTEs) via a high‐throughput gravure printing process is reported. By varying the blend ratio of the mixture solvent and the concentration of the silver nanowire (AgNW) inks, the surface tension, volatilization rate, and viscosity of the AgNW ink can be tuned to meet the requirements of gravure printing process. Following this method, uniformly printed AgNW films are prepared. Highly conductive FTEs with a sheet resistance of 10.8 Ω sq⁻¹ and a high transparency of 95.4% (excluded substrate) are achieved, which are comparable to those of indium tin oxide electrode. In comparison with the spin‐coating process, the gravure printing process exhibits advantages of the ease of large‐area fabrication and improved uniformity, which are attributed to better ink droplet distribution over the substrate. 0.04 cm² polymer solar cells based on gravure‐printed AgNW electrodes with PM6:Y6 as the photoactive layer show the highest power conversion efficiency (PCE) of 15.28% with an average PCE of 14.75 ± 0.35%. Owing to the good uniformity of the gravure‐printed AgNW electrode, the highest PCE of 13.61% is achieved for 1 cm² polymer solar cells based on the gravure‐printed FTEs.

An amphiphilic dendritic block copolymer is developed to serve as an efficient surface modifier of ZnO electron‐transporting layer in an organic photovoltaic device. When using an interlayer based on its hybridization with gold nanoparticles, the device can deliver improved performance and possess a lifetime of over 1.79 years when stored at room temperature in inert conditions.

Abstract

Herein, interfacial engineering is demonstrated to improve the thermal stability of non‐fullerene bulk‐heterojunction (BHJ) OPVs to a practical level. An amphiphilic dendritic block copolymer (DBC) is developed through a facile coupling method and employed as the surface modifier of ZnO electron‐transporting layer in inverted OPVs. Besides showing distinct self‐assembly behavior, the synthesized DBC possesses high compatibility with plasmonic gold nanoparticles (NPs) due to the constituent malonamide and ethylene oxide units. The hybrid DBC@AuNPs interlayer is shown to improve device's performance from 14.0% to 15.4% because it enables better energy‐level alignment and improves interfacial compatibility at the ZnO/BHJ interface. Moreover, the DBC@AuNPs interlayer not only improves the interfacial thermal stability at the ZnO/BHJ interface but also endows a more ideal BHJ morphology with an enhanced thermal robustness. The derived device reserves 77% of initial PCE after thermal aging at 65 °C for 3000 h and yields an extended T ₈₀ lifetime of >1100 h when stored at a constant thermal condition at 65 °C, outperforming the control device. Finally, the device is evaluated to possess a T ₈₀ lifetime of over 1.79 years at room temperature (298 K) when stored in an inert condition, showing great potential for commercialization.

An anion/cation synergy strategy is proposed by the incorporation of ZnI₂ in CsPbI₃ quantum dots (QDs) to improve the stability and photoelectric properties. The obtained Zn:CsPbI₃ QDs show lower defect state density and enhanced structural stability. Perovskite quantum dot solar cells fabricated with Zn:CsPbI₃ QDs exhibit a champion power conversion efficiency over 16%.

Abstract

All‐inorganic CsPbI₃ quantum dots (QDs) have shown great potential in photovoltaic applications. However, their performance has been limited by defects and phase stability. Herein, an anion/cation synergy strategy to improve the structural stability of CsPbI₃ QDs and reduce the pivotal iodine vacancy (V _I) defect states is proposed. The Zn‐doped CsPbI₃ (Zn:CsPbI₃) QDs have been successfully synthesized employing ZnI₂ as the dopant to provide Zn²⁺ and extra I⁻. Theoretical calculations and experimental results demonstrate that the Zn:CsPbI₃ QDs show better thermodynamic stability and higher photoluminescence quantum yield (PLQY) compared to the pristine CsPbI₃ QDs. The doping of Zn in CsPbI₃ QDs increases the formation energy and Goldschmidt tolerance factor, thereby improving the thermodynamic stability. The additional I⁻ helps to reduce the V _I defects during the synthesis of CsPbI₃ QDs, resulting in the higher PLQY. More importantly, the synergistic effect of Zn²⁺ and I⁻ in CsPbI₃ QDs can prevent the iodine loss during the fabrication of CsPbI₃ QD film, inhibiting the formation of new V _I defect states in the construction of solar cells. Consequently, the anion/cation synergy strategy affords the CsPbI₃ quantum dot solar cells (QDSC) a power conversion efficiency over 16%, which is among the best efficiencies for perovskite QDSCs.

Novel interface polarization induced field‐effect passivation based on amorphous transition metal oxide is developed for efficient and ambient‐air‐stable perovskite solar cells. Comprehensive insights into the interaction between the field‐effect passivation, interface polarities, and the performance of the device have been elucidated in detail.

Abstract

Organolead halide hybrid perovskite solar cells (PSCs) have become a shining star in the renewable devices field due to the sharp growth of power conversion efficiency; however, interfacial recombination and carrier‐extraction losses at heterointerfaces between the perovskite active layer and the carrier transport layers remain the two main obstacles to further improve the power conversion efficiency. Here, novel field‐effect passivation has been successfully induced to effectively suppress the interfacial recombination and improve interfacial charge transfer by incorporating interfacial polarization via inserting a high work function interlayer between perovskite and holes transport layer. The charge dynamics within the device and the mechanism of the field‐effect passivation are elucidated in detail. The unique interfacial dipoles reinforce the built‐in field and prevent the photogenerated charges from recombining, resulting in power conversion efficiency up to 21.7% with negligible hysteresis. Furthermore, the hydrophobic interlayer also suppresses the perovskite decomposition by preventing the moisture penetration, thereby improving the humidity stability of the PSCs (>91% of the initial power conversion efficiency (PCE) after 30 d in 65 ± 5% humidity). Finally, several promising research perspectives based on field‐effect passivation are also suggested for further conversion efficiency improvements and photovoltaic applications.

The excited state characteristics of organic hole transport materials in perovskite photovoltaics (PVs), such as transition dipole moment, is confirmed to be a critical factor in improving the built‐in potential of devices for efficient charge extraction along with reduced carrier recombination. Moreover, the aggregation property of the organic semiconductor can have a synergistic effect with its excited state property for high‐efficiency perovskite PVs.

Abstract

Intrinsic characteristics of organic semiconductor‐based hole transport materials (HTMs) such as facile synthesizability, energy level tunability, and charge transport capability have been highlighted as crucial factors determining the performances of perovskite photovoltaic (PV) cells. However, their properties in the excited state have not been actively studied, although PVs are operated under solar illumination. Here, the characteristics of organic HTMs in their excited state such as transition dipole moment can be a decisive factor that can improve built‐in potential of PVs, consequently enhancing their charge extraction property as well as reducing carrier recombination. Moreover, the aggregation property of organic semiconductors, which has been an essential factor for high‐performance organic HTMs to improve their carrier transport property, can induce a synergistic effect with their excited state property for the high‐efficiency perovskite PVs. Additionally, it is also confirmed that their optical bandgaps, manipulated to have their absorption in the UV region, are beneficial to block UV light that degrades the quality of perovskite, consequently improving the stability of perovskite PV in p–i–n configuration. As a proof‐of‐concept, a model system, composed of triarylamine and imidazole‐based organic HTMs, is designed, and it is believed that this strategy paves a way toward high‐performance and stable perovskite PV devices.

In the past decade, the perovskite solar cell (PSC) has attracted tremendous attention. The electron transport layer (ETL) is one of the most important functional layers in PSCs. This review provides an up‐to‐date summary of the developments in inorganic electron transport materials for PSCs. Strategies to optimize the ETL, an outlook on current challenges and further development are discussed.

Abstract

In the past decade, the perovskite solar cell (PSC) has attracted tremendous attention thanks to the substantial efforts in improving the power conversion efficiency from 3.8% to 25.5% for single‐junction devices and even perovskite‐silicon tandems have reached 29.15%. This is a result of improvement in composition, solvent, interface, and dimensionality engineering. Furthermore, the long‐term stability of PSCs has also been significantly improved. Such rapid developments have made PSCs a competitive candidate for next‐generation photovoltaics. The electron transport layer (ETL) is one of the most important functional layers in PSCs, due to its crucial role in contributing to the overall performance of devices. This review provides an up‐to‐date summary of the developments in inorganic electron transport materials (ETMs) for PSCs. The three most prevalent inorganic ETMs (TiO₂, SnO_2, and ZnO) are examined with a focus on the effects of synthesis and preparation methods, as well as an introduction to their application in tandem devices. The emerging trends in inorganic ETMs used for PSC research are also reviewed. Finally, strategies to optimize the performance of ETL in PSCs, effects the ETL has on J–V hysteresis phenomenon and long‐term stability with an outlook on current challenges and further development are discussed.

In article number 2008300, Liangyou Lin, Xianbao Wang, Gregory J. Wilson, and co‐workers review the state‐of‐the‐art for inorganic electron transport materials (ETMs) in perovskite solar cells. Depicted are typical device architectures including the most prevalent inorganic ETMs (TiO₂, SnO₂ and ZnO) that have enabled champion single‐junction devices with up to 25.2% power conversion efficiency.

Slot die coating is used to fabricate high efficiency (power conversion efficiencies (PCE) > 11.0%), stable organic solar cells based on a donor PTB7‐Th and nonfullerene acceptor IEICO‐4F. The 11% small area and 1 cm² devices with a PCE of 9.63% show the scalability of the technique. The highest light utilization efficiency of 5.26% with a PCE of 9.07% is achieved for the all solution processed semi‐transparent solar cell.

Abstract

Slot‐die (SD) coating is used to fabricate fully solution processed organic solar cells (OSCs) based on a blend of high performance donor polymer (PTB7‐Th) and a non‐fullerene acceptor (IEICO‐4F) for stable devices over extended periods of operation. The optimization of a sequential deposition process of transport and active layers, under ambient conditions, enable high efficiency slot‐die coated solar cells with remarkable power conversion efficiencies (PCE) > 11.0% to bridge the gap between lab‐to‐fab. Fully slot‐die coated inverted OSCs are demonstrated with efficiencies reaching 11% along with 1 cm² devices, proving the scalability and reproducibility of the proposed technique. Further, replacing the evaporated Ag electrode with solution processed Ag nanowire (AgNW) electrodes shows the highest light utilization efficiency of 5.26% for semi‐transparent OSC with a PCE of 9.07% and average visible transmission of 58%.

An electrospray printing technique is developed to continuously print the TiO₂ electron transport layer, perovskite layer, and carbon layer, enabling a cost‐effective device. The electrospray technique is capable of printing uniform, compact, and high adhesion layers with controllable dimensions and patterns. This work demonstrates a fully printed low‐cost solar cell and provides a feasible process for perovskite solar cells to initial industrialization.

Abstract

With the power conversion efficiencies of perovskite solar cells (PSCs) exceeding 25%, the PSCs are a step closer to initial industrialization. Prior to transferring from laboratory fabrication to industrial manufacturing, issues such as scalability, material cost, and production line compatibility that significantly impact the manufacturing remain to be addressed. Here, breakthroughs on all these fronts are reported. Carbon‐based PSCs with architecture fluorine doped tin oxide (FTO)/electron transport layer/perovskite/carbon, that eliminate the need for the hole transport layer and noble metal electrode, provide ultralow‐cost configuration. This PSC architecture is manufactured using a scalable and industrially compatible electrospray (ES) technique, which enables continuous printing of all the cell layers. The ES deposited electron transport layer and perovskite layer exhibit properties comparable to that of the laboratory‐scale spin coating method. The ES deposited carbon electrode layer exhibits superior conductivity and interfacial microstructure in comparison to films synthesized using the conventional doctor blading technique. As a result, the fully ES printed carbon‐based PSCs show a record 14.41% power conversion efficiency, rivaling the state‐of‐the‐art hole transporter‐free PSCs. These results will immediately have an impact on the scalable production of PSCs.

Inorganic perovskite CsPbI₂Br is applied to prepare high‐performance semitransparent perovskite solar cells (ST‐PSCs). (Chloromethylene)‐dimethylammonium chloride as an additive is introduced into the perovskite precursor to favor high‐quality CsPbI₂Br perovskite films. Through optimizing the perovskite film, interface, and electrode type, the efficiency of the ST‐PSC reaches 14.01% and 10.36% under an average visible transmittance (AVT) of 31.7% and 40.9%, respectively.

Abstract

Thanks to the tunable bandgap and excellent photoelectric characteristics, perovskites have been widely used in semitransparent solar cells (ST‐SCs). Most works present unsatisfactory power conversion efficiencies (PCEs) through reducing the thickness of the perovskite films because there is a trade‐off between PCE and average visible transmittance (AVT). As a consequence, most PCEs are less than 12% when the AVT is higher than 20% due to the limited voltage (V _oc) and short‐circuit current (J _sc). Herein, a strategy of intermediate adduct (IMAT) engineering is developed to improve the film quality of the inorganic perovskite CsPbI₂Br, which is a challenging issue to limit its performance of efficiency and stability. A normal n–i–p‐structured PSC based on the optimal CsPbI₂Br film delivers a PCE of 16.02% with excellent stability. Furthermore, through optimizing the electrode type and interface, the ST‐PSC shows a high V _oc larger than 1.2 V and the PCE reaches 14.01% and 10.36% under an AVT of 31.7% and 40.9%, respectively. This is the first demonstration of a CsPbI₂Br ST‐PSC, and it outperforms most of other types of perovskites.

In article number 2001482, Helen Hejin Park, Jangwon Seo, and co‐workers introduce copper oxide by pulsed‐chemical vapor deposition as a buffer layer, which protects the organic hole transport layer from sputtering damage during sputtering of the transparent conducting oxide. On the cover the authors illustrate the precursors used during their copper oxide buffer layer approach integrated in semitransparent perovskite solar cell applications.