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Finding remarkable hole-transporting materials (HTMs) for perovskite solar cells (PSCs) is crucial but challenging, and rationally regulating the acceptor structure is one of the most effective strategies. In this work, a novel electron-withdrawing moiety of thiadiazolophenanthroline (TPT) was first exploited as the acceptor structure of donor–acceptor–donor (D–A–D)-type HTMs. The isolated molecular and interfacial properties of TPT-based HTMs (SM-4) were methodically investigated by comparing with the simulated results of benzothiadiazole (BT, SM-1) and phenanthrothiadiazole (PT, SM-2) acceptors. Theoretical simulations manifest that SM-4 displays a more negative HOMO energy and larger hole mobility than SM-1 and SM-2. The higher mobility of SM-4 is derived from the larger hole transfer integral due to easier intermolecular orbital overlap. Moreover, the better optical excitation property, smaller exciton binding energy, and profitable solubility and stability are shown for SM-4. Furthermore, interfacial calculations reveal that advantageous photon-induced excitation dissociation can be anticipated at the interface because of greater interfacial charge redistribution and more suitable energy levels. Overall, our simulations suggest that the designed TPT-based acceptor molecule holds great promise as a potential HTM candidate, providing support for more efficient PSCs. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have been rapidly developed in recent years due to their excellent photovoltaic performance, which has been actively promoted by many researchers. However, interfacial non-radiative compounding hinders further improvement of their device performance. Buried interface modification strategies can minimize the non-radiative compounding within the interface, resulting in highly efficient and stable PSCs. In this review, we summarize the recent advances in the development of multiple classes of materials applied to buried interface engineering for the preparation of highly efficient and stable PSCs, including the development of organic, inorganic, and polymeric materials. The important role of buried interfaces in regulating energy alignment, passivating surface defects, modulating morphology, etc. have been discussed. Furthermore, we propose strategies to reduce nonradiative composites at interfaces. Finally, potential developments and challenges of buried interfaces for high performance stabilized PSCs are presented. [ABSTRACT FROM AUTHOR]

Herein, we report a novel and powerful approach developed to lower the manufacturing costs of PSCs and make them powerful and cost-effective technology through identifying more efficient and low-cost dopant-free hole-transport materials (HTMs) for PSCs by avoiding the shotgun approach of synthesizing hundreds or thousands of HTMs, fabricate devices and characterize them to identify the best performing candidate(s). With these in mind, the primary objective of this study is to develop a machine learning model extracted from automated-quantitative structure–property relationship (autoQSPR) models that could accurately predict various photovoltaic properties, including power conversion efficiency (PCE), open-circuit photovoltage (VOC), and short-circuit photocurrent (JSC), of dopant-free HTM-based PSCs. High-efficacy AutoQSPR models capable of accurately predicting photovoltaic properties were developed by considering experimental photovoltaic property data sets from dopant-free HTMs used in the fabrication of PSCs with different architectures, e.g., conventional (n–i–p) and inverted (p–i–n), which are fabricated using methyl ammonium lead halides (MALHs) or mixed cation lead halides, were used to develop high efficacy autoQSPR models capable of accurate predictions of photovoltaic properties. The Schrodinger Suite was utilized to build autoQSPR models to predict PCE, VOC, and JSC utilizing different kinds of molecular descriptors such as 2D binary fingerprints, one dimensional (1D), two dimensional (2D), and three dimensional (3D). Notably, 2D binary fingerprint descriptors generate models that outperform 1D, 2D, and 3D molecular descriptors calculated using the well-known PaDEL calculator. The developed autoQSPR models were improved when the PSC configurations were considered and a significant predictive ability (test set Q2 > 0.5) was achieved for all autoQSPR models that involved the use of 2D binary fingerprint descriptors. The model confidence was validated by the utilization of dopant-free HTMs that were not present in the original dataset used to build the models. Furthermore, the most efficient models were used to propose potential HTM candidates to benefit the scientific community and scholars. [ABSTRACT FROM AUTHOR]

Two novel asymmetric phthalocyanine derivatives, ZnPc-1 and ZnPc-2, are synthesized to enhance charge transfer properties and mitigate deep-level traps on the perovskite surface using electron-rich nitrogen atoms. PSCs with ZnPc-1 and ZnPc-2 as hole-transporting materials (HTMs) achieved power conversion efficiencies (PCEs) of 12.11% and 8.98%, respectively. Incorporating a small amount of PMMA into the HTM solution significantly improved performance, resulting in PCEs of 16.2% and 12.5% for ZnPc-1 and ZnPc-2, respectively. The addition of PMMA enhances conductivity and prevents moisture intrusion, boosting both the efficiency and stability of PSCs. [ABSTRACT FROM AUTHOR]

Passivation defects and reducing charge recombination are of great importance in enhancing 2D perovskite solar cells' (PSCs) performance. Herein, a novel additive (TEMPIC) is introduced into 2D PSCs to improve photovoltaic properties of the device, which are mainly attributed to passivated trap-states and reduced charge recombination in device. [ABSTRACT FROM AUTHOR]

Interfacial engineering, especially the modulation of the buried interface, has a strong impact on the photovoltaic performance of perovskite solar cells (PSCs). In this study, a natural chemical, riboflavin (VB2), was introduced to modify the TiO2/perovskite interface in planar PSCs. As a result, oxygen defects in TiO2 were passivated, and the quality of the perovskite film, together with the energy level arrangement, was optimized. Finally, PSCs modified with VB2 showed a significant increase in power conversion efficiency (PCE) from 19.2% to 21.50%. Additionally, PSCs modified with VB2 exhibited better long-term stability by maintaining 75.8% of their original PCE after 700 hours of aging at a relative humidity (RH) of 30% ± 5% and at room temperature. [ABSTRACT FROM AUTHOR]

The buried interface between perovskite and the electron transport layer (ETL) played a crucial role in improving the power conversion efficiency (PCE) and stability of n-i-p structured perovskite solar cells (PSCs). Commercially prepared SnO2-based ETL films often suffered from severe interface defects, imperfect energy level alignment, and uncontrollable perovskite nucleation sites, hindering the achievement of highly efficient and stable PSCs. In this study, the hindering factors of commercial SnO2 ETL films were all addressed by the incorporation of a non-toxic multifunctional molecule, natural sodium lignosulfonate (SL) into the SnO2 ETL precursor, and ameliorated perovskite films were obtained. As a result, the PCE of a reference device (19.60%) was improved to 21.12% after doping with SL. Furthermore, unencapsulated SLdoped devices exhibited excellent environmental stability. After 840 h of storage at ~20% RH, the SLmodified device retained ~83% of its initial PCE, well exceeding the control device (~13%). In addition, our findings suggest a novel strategy aimed at improving the efficiency and stability of PSCs by the incorporation of non-toxic multifunctional molecules such as natural SL. [ABSTRACT FROM AUTHOR]

The buried interface between perovskite and the electron transport layer (ETL) played a crucial role in improving the power conversion efficiency (PCE) and stability of n-i-p structured perovskite solar cells (PSCs). Commercially prepared SnO2-based ETL films often suffered from severe interface defects, imperfect energy level alignment, and uncontrollable perovskite nucleation sites, hindering the achievement of highly efficient and stable PSCs. In this study, the hindering factors of commercial SnO2 ETL films were all addressed by the incorporation of a non-toxic multifunctional molecule, natural sodium lignosulfonate (SL) into the SnO2 ETL precursor, and ameliorated perovskite films were obtained. As a result, the PCE of a reference device (19.60%) was improved to 21.12% after doping with SL. Furthermore, unencapsulated SLdoped devices exhibited excellent environmental stability. After 840 h of storage at ~20% RH, the SLmodified device retained ~83% of its initial PCE, well exceeding the control device (~13%). In addition, our findings suggest a novel strategy aimed at improving the efficiency and stability of PSCs by the incorporation of non-toxic multifunctional molecules such as natural SL. [ABSTRACT FROM AUTHOR]

An instant p-doping strategy employing 4-tert-butyl-2-chloropyridine and tert-butyl peroxybenzoate for the spiro-OMeTAD hole-transport layer (HTL) in perovskite solar cells (PSCs) is proposed to replace the conventional 4-tert-butylpyridine-doped HTL. The novel doping process eliminates the formation of pores in the HTL. Meanwhile, a 21.4% efficiency is achieved on the corresponding absolute methylammonium-free PSCs with significantly improved thermal and moisture stability. [ABSTRACT FROM AUTHOR]

Due to the hydrophilicity and black-phase instability of FA perovskites, ambient humidity is an unavoidable issue in the processing of perovskite solar cells (PSCs). MACl is among the most popular additives for improving perovskite films, but our experiments confirm that the direct addition of MACl into the precursor solution deteriorates the stability of the final α-FAPbI3 films in humid air, which is attributed to the unwanted pinholes induced by MACl volatilization. To solve this problem, a novel confined-space annealing strategy (CSA) is intentionally developed to control the amount of MACl at a low level. Through retarding the volatilization of MACl and blocking moisture ingress, dense and δ-phase-free FAPbI3 films with excellent crystallinity and stability are achieved at 100 °C under high humidity (RH: 60 ± 10%). We further compare the same amounts of MAI and FACl additives with MACl, discovering that only when MA and Cl work together can pure α-FAPbI3 films be obtained; therefore, a mechanism of MA-assisted nucleation and Cl-induced diffusion recrystallization is inferred. As a result, the PSCs employing optimal films yield a champion power conversion efficiency (PCE) of 17.27% and retain over 90% of the initial PCE after exposure to high humidity for 480 h. Our results offer deep insights into the thermodynamic and kinetic behaviors of MA and Cl in film growth and are beneficial for air-processed FA-based PSCs for commercial application. [ABSTRACT FROM AUTHOR]

A new class of fluorinated cyclopenta[2,1-b:3,4-b′]dithiophene (CPDT)-based small molecules, namely YC-oF, YC-mF, and YC-H, are demonstrated as hole-transporting materials (HTMs) for high-performance perovskite solar cells (PSCs). PSCs employing YC-oF as the HTM delivered an excellent efficiency of 22.41% with encouraging long-term stability. [ABSTRACT FROM AUTHOR]

Hole transport materials (HTMs) are an integral part of highly efficient perovskite solar cells (PSCs). Although the traditional HTM Spiro-OMeTAD achieves excellent performance, its high cost limits its future large-scale application during commercialization of PSCs. Therefore, it is essential to develop low-cost and efficient alternative HTMs. Herein, we successfully synthesize two novel HTMs DTP-1 and DTP-2 by employing methoxy-substituted terthienyl (DTP) as the core unit and adjusting the electron donors. Research indicates that the introduction of methoxy groups on the core unit enhances its electron donating ability; thus, the capping groups with slightly lower electron donating ability should be adopted to get well-matched energy levels. After optimization, the best-performing power conversion efficiency (PCE) of DTP-1 based PSCs is 21.1%, which is much higher than those of PSCs based on DTP-2 (15.6%) and THP-1 (20.5%). Furthermore, under the conditions of RH 30–45% and room temperature, the DTP-1-based devices maintain 80.5% of the initial PCE after aging for 840 h, which is better than those of DTP-2 (22.0%) and THP-1 (71.5%). [ABSTRACT FROM AUTHOR]

We report a solution-processing method to prepare an inorganic LaNiO3 (LNO) hole-transport layer (HTL) under low temperature (<150 °C) for the first time. The inverted PSCs prepared with LNO exhibit high UV-stability and promising efficiency (17.15%). Our preliminary results show great potential for LNO HTL in the fabrication of efficient and photostable inverted perovskite solar cells (PSCs). [ABSTRACT FROM AUTHOR]

2D/3D perovskite heterojunctions exhibit promising prospects in the improvement of efficiency and stability of perovskite solar cells (PSCs). However, many challenges remain in the development of high-quality 2D/3D heterojunctions, such as a reliable pathway to control the perovskite phase and generally poor performance in inverted (p–i–n) devices, which limit their commercialization. Fortunately, many excellent works have proposed lots of strategies to solve these challenges, which have triggered a new wave of research on 2D/3D perovskite heterojunctions in recent years. In this paper, the latest research progress and the critical factors involved in the modulating mechanisms of PSCs with 2D/3D heterojunctions have been summarized and laid out systematically. The advantages of constructing 2D/3D perovskite heterojunctions in PSCs are highlighted, and the problems and related solutions of low-dimensional perovskites as passivation layers towards high-performance PSCs are also discussed in depth. Finally, the prospects of 2D/3D perovskite heterojunctions utilized in the passivation strategies to further improve the photovoltaic performance of PSCs in the future have been presented. [ABSTRACT FROM AUTHOR]

Optimizing electron transport layers (ETLs) is a significant way to enhance the photovoltaic performance and stability of inverted perovskite solar cells (PSCs). Herein, we introduce a strategy focused on binarymixed organic ETLs, which dopes an n-type small organic molecule, m-ITTC, into the fullerene [6,6]- phenyl C61-butyric acid methyl ester (PCBM) ETLs to fabricate a binary-mixed organic ETLs for use in inverted PSCs. The binary-mixed organic ETLs have suitable energy level alignment at the interface between the perovskite and ETLs, and thus the charge recombination behavior is modified. The PSCs modified with the binary-mixed organic ETLs exhibit a power conversion efficiency (PCE) of 15.62% with negligible hysteresis. Additionally, the binary-mixed organic ETLs can not only effectively prevent moisture intrusion, but also alleviate aggregation under continuous operation, so as, compared to PCBM ETLs, the devices with the binary-mixed organic ETLs exhibit better stability with a T95 of the bestperforming devices exceeding 200 h. This work represents a simple and effective way to enhance the efficiency and stability of PSCs. [ABSTRACT FROM AUTHOR]

Benzoxadiazole derivatives have been rarely employed in designing non-fused ring electron acceptors (NFREAs). Herein, two novel NFREAs consisting of uniform difluorobenzoxadiazole cores, cyclopentadithiophene bridges, and different fluorinated/chlorinated dicyanoindanone end-groups were developed and named as BOCIC-4F and BOCIC-4Cl, respectively. Apart from the differences in physical properties, different halogenations on NFREAs simultaneously lead to variations in compatibility with different polymer donors. In succession, the polymer donors, PBDB-T and PBDB-TF, were employed to form different donor:acceptor pairs with two NFREAs to estimate the compatibility in varied blends. Polymer solar cells (PSCs) based on fluorinated BOCIC-4F yielded the best photovoltaic performance with nonhalogenated PBDB-T. However, the efficiency diminished when PBDB-T was changed to halogenated PBDB-TF. In contrast, the chlorinated BOCIC-4Cl, which achieved the poorest performance with PBDB-T, could work better with PBDB-TF. Disparities in aggregation behaviors, miscibility factors, blend morphologies, and carrier dynamics derived from the different halogenations on NFREAs were responsible for the contrary compatibility in different blends. This work demonstrates the potential of benzoxadiazole derivatives in the design of efficient NFREAs. Moreover, these results will also be useful for constructing high-performance PSCs by estimating the compatibility of various donor:acceptor pairs. [ABSTRACT FROM AUTHOR]

Charge transporting layers (CTLs) are essential components of perovskite solar cells (PSCs) that significantly impact their performance and stability. Metal oxide CTLs are extensively used for PSCs owing to their high transparency, stability, and low-cost synthetic routes. However, metal oxide CTLs still have limitations such as excess surface defects and mismatched energy band alignment with the perovskite layer. To resolve these issues, various metal oxide materials and processes have been developed. Herein, we systematically review the recent developments in metal oxide CTLs for PSCs. We discuss the importance of nanostructure tuning, doping, and surface and interface functionalization approaches for metal oxide CTLs to enhance PSC performance and stability. Finally, the future perspectives for the further development of the metal oxide CTLs for PSCs are highlighted. [ABSTRACT FROM AUTHOR]

Li@PCBM, the first neutral Li@C60 derivative, was synthesized. The Li@PCBM exists in a monomer-dimer equilibrium in solution but as a monomer in the PCBM matrix. The fully dispersed Li@PCBM n-doped the surrounding empty PCBM, raising the Fermi level by 0.13 eV compared with the undoped PCBM film. The hybrid films were utilized as an ETL for PSCs, promoting the efficiency of the device. [ABSTRACT FROM AUTHOR]

Au nanochains with a coupled plasmonic nanostructure were first introduced into PEDOT:PSS used as a hole transport layer to fabricate mixed tin–lead PSCs. The improved electrical properties and the promotion of optical absorption contributed to a high PCE of 19.2%. Moreover, the PSCs show substantial enhancement in stability. [ABSTRACT FROM AUTHOR]

CsPbIBr2 has attracted intense attention as an absorber material of all-inorganic perovskite solar cells (PSCs), owing to its upgraded stability and suitable bandgap. Yet, the efficiency level of CsPbIBr2 PSCs is still far below those of other all-inorganic PSCs, largely because of the inferior morphology and crystallization properties of solution-processed CsPbIBr2 films. Herein, we propose for the first time an in situ polymer-covered annealing strategy to modify the crystallization behavior of one-step-deposited CsPbIBr2 film, which is performed through spin-coating of poly(methyl methacrylate) (PMMA) solution upon CsPbIBr2 precursor film before annealing. By optimizing the concentration of PMMA solution, a CsPbIBr2 film with large-size grains, [110]-preferred orientation, reduced halide segregation, stoichiometric composition, and decreased non-radiative recombination can be acquired, which lead to the improved transport and suppressed non-radiative recombination of charge carriers for the resulting PSC. Hence, the optimum carbon-electrode PSC exhibits a significantly enhanced efficiency from 8.71% to 10.50%, which is better than that of nearly all the CsPbIBr2 PSCs with the same configuration reported earlier. [ABSTRACT FROM AUTHOR]

Two dimensional (2D) perovskite materials, are more stable than 3D perovskite materials, which could solve the stability issue of perovskite solar cells (PSCs). However, the photovoltaic conversion efficiency (PCE) of PSCs based on 2D perovskite materials was low, due to the high dielectric and quantum confinement of 2D perovskite. In this work, we propose a solvent-assisted method to prepare 2D perovskite films, where the solvent was distributed in a gradient. Therefore, the top-down crystallization process of 2D perovskite can be accurately controlled. The PCE of PSCs fabricated by the solvent-assisted method was enhanced by 48%, compared with the control device. For the packaged devices, the stability test demonstrated that 94% of the initial PCE was still maintained after 1500 hours of storage (25 °C, RH 40%). After carefully analyzing the photophysical process of the carriers in the PSCs based on 2D perovskite, the enhanced carrier transfer mechanism of the solvent-assisted method has been proposed. [ABSTRACT FROM AUTHOR]

A norbornene homopolymer with hole-transporting 2,7-bis(di-p-anisylamino)fluorene side chains is compared to the widely used spiro-OMeTAD as a hole-transport material (HTM) in negative-intrinsicpositive (n-i-p) perovskite solar cells (PSCs). PSCs fabricated using p-doped homopolymer achieve a power conversion efficiency of 15.5%, comparable to that of cells incorporating p-doped spiro-OMeTAD as the HTM. However, half-devices made with the polymer exhibit improved light and heat stability in comparison to those incorporating spiro-OMeTAD. [ABSTRACT FROM AUTHOR]

Three asymmetric spiro[fluorene-9,9′-xanthene] (SFX)-based hole transporting materials (HTMs) with N-(p-methoxyphenyl)-N′-(9,9′-dimethylfluoren-2-yl)amino (FPA) substituents, which are termed SFX-F, SFX-FM, and SFX-FP, have been synthesized by a facile process. When modifying the number and position of FPA substituents in the HTMs, it was found that there is no significant variation in the HOMO energy by increasing the number of FPA groups, while the thermal stability is governed by the substitution position. SFX-FM, which contains two meta-substituted FPA groups on the xanthene unit, exhibits a suitable HOMO energy level (−5.24 eV) and a strikingly high Tg (154 °C). In addition, SFX-FM also shows better film-forming properties and excellent hydrophobicity, which is conducive to fabricating high-performance devices. Noticeably, the PSCs based on SFX-FM achieved a power conversion efficiency (PCE) of 17.29% under AM 1.5 G illumination at 100 mW cm−2, unprecedentedly outperforming PSCs based on spiro-OMeTAD (15.14%). [ABSTRACT FROM AUTHOR]

Hydroxyapatite nanoparticles (HAP NPs) are blended with TiO2 NPs to prepare mixed mesoporous scaffolds which are used to prepare high efficiency perovskite solar cells (PSCs) with a best power conversion efficiency (PCE) of 20.98%. HAP not only increases the PCE but also limits the concentration of Pb released in water from intentionally broken PSCs by ion sequestration thereby potentially offering a promising in-device fail-safe system. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have reached their highest efficiency with the state-of-the-art hole-transporting material (HTM) spiro-OMeTAD. However, the relatively low conductivity and high cost of this material significantly limit the commercialization of this promising technology. In this work, a low-cost, asymmetric HTM containing a carbazole core and peripheral triphenylamine moieties, named Cz-3OMeTAD, was designed and synthesized via a facile three-step synthetic procedure and employed successfully in planar CH3NH3PbI3 PSCs. The optical and electrochemical data of the asymmetric HTM Cz-3OMeTAD exhibited appropriate energy levels for efficient interfacial charge transfer with the perovskite. The asymmetric propeller-shaped Cz-3OMeTAD has a relatively high mobility value of 1.42 × 10−3 cm2 V−1 s−1, beneficial for the PSC performance. Moreover, steady-state PL and time-resolved PL measurements indicate successful hole extraction properties of Cz-3OMeTAD from the perovskite at the perovskite/HTM interface. Consequently, the Cz-3OMeTAD-based devices achieved a high efficiency of 16.36% in PSCs under 1 sun conditions, comparable with the efficiency obtained for the reference cell using spiro-OMeTAD. Thus, our result demonstrated the asymmetric carbazole-based material as a new class of HTM for highly efficient PSCs. [ABSTRACT FROM AUTHOR]

Recently, perovskite solar cells (PSCs) have attracted much attention owing to their high power conversion efficiency (25.2%) and low fabrication cost. However, the short lifetime under operation is the major obstacle for their commercialization. With efforts from the entire PSC research community, significant advances have been witnessed to improve the device operational stability, and a timely summary on the progress is urgently needed. In this review, we first clarify the definition of operational stability and its significance in the context of practical use. By analyzing the mechanisms in established approaches for operational stability improvement, we summarize several effective strategies to extend device lifetime in a layer-by-layer sequence across the entire PSC. These mechanisms are discussed in the contexts of chemical reactions, photo-physical management, technological modification, etc., which may inspire future R&D for stable PSCs. Finally, emerging operational stability standards with respect to testing and reporting device operational stability are summarized and discussed, which may help reliable device stability data circulate in the research community. The main target of this review is gaining insight into the operational stability of PSCs, as well as providing useful guidance to further improve their operational lifetime by rational materials processing and device fabrication, which would finally promote the commercialization of perovskite solar cells. [ABSTRACT FROM AUTHOR]

In the last five years, the tremendous progress achieved in the field of polymer solar cells (PSCs) has attracted extensive attention to this emerging technology for exploiting renewable energy. Owing to their excellent optoelectronic features and outstanding manufacturability for film deposition, wide bandgap (WBG) polymer donors have become a leading component in bulk heterojunction layers and thus, a correlative review focusing on their molecular design, aggregation behavior and photovoltaic properties is necessary. In this feature article, we summarize our recent efforts in developing WBG polymer donors and understanding the charge separation and non-radiative recombination energy loss in high-performance non-fullerene (NF) PSCs. We also discuss the opportunities and challenges towards the realization of the commercialization of NF PSCs based on WBG polymer donors. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) reached a certified 23.7% efficiency in 2018 by boosting their surprisingly high open-circuit voltage (VOC) and photocurrent. The suppressed recombination in PSCs significantly cut down the voltage loss between the bandgap energy and VOC, which encouraged the VOC to reach closer to the bandgap. In addition, the photocurrent is considerably closer to the theoretical value at a given bandgap, leaving almost no room for further improvement. This remarkable development in the performance of PSCs is mainly ascribed to high-quality perovskite material being consistently tailored in the progress of technology. At the beginning of the progress, the morphology of the perovskite was a major target for improvement to enhance the crystal quality. The need for compositional engineering of the perovskite was raised in later stages of the progress by considering the benefits from different compositions of perovskites and their structural stability. Here we review the overall progress in perovskite materials from two perspectives: morphological progress and compositional progress. [ABSTRACT FROM AUTHOR]