awn

A universal approach is reported to fabricate perovskite films by incorporating inorganic CsPbBr₃ quantum dots (QDs) into halide perovskite bulk films. Upon post-annealing, the released elements from QDs compensate vacancies, and hydrophobic ligands on QDs passivate under-charged Pb atoms and self-assemble on surface. Therefore, the resulting films with reduced trap density, suppressed phase segregation, improved surface uniformity and enhanced stability are enabled.

Abstract

Structural defects are ubiquitous for polycrystalline perovskite films, compromising device performance and stability. Herein, a universal method is developed to overcome this issue by incorporating halide perovskite quantum dots (QDs) into perovskite polycrystalline films. CsPbBr₃ QDs are deposited on four types of halide perovskite films (CsPbBr₃, CsPbIBr₂, CsPbBrI₂, and MAPbI₃) and the interactions are triggered by annealing. The ions in the CsPbBr₃ QDs are released into the thin films to passivate defects, and concurrently the hydrophobic ligands of QDs self-assemble on the film surfaces and grain boundaries to reduce the defect density and enhance the film stability. For all QD-treated films, PL emission intensity and carrier lifetime are significantly improved, and surface morphology and composition uniformity are also optimized. Furthermore, after the QD treatment, light-induced phase segregation and degradation in mixed-halide perovskite films are suppressed, and the efficiency of mixed-halide CsPbIBr₂ solar cells is remarkably improved to over 11% from 8.7%. Overall, this work provides a general approach to achieving high-quality halide perovskite films with suppressed phase segregation, reduced defects, and enhanced stability for optoelectronic applications.

The phase segregation of mixed-halide perovskite solar cells induces a locally shifted bandgap, hinders the charge-carrier transport, and increases the bulk recombination. By suppressing the phase segregation, the open-circuit voltage is improved from 1.15 to 1.20 V.

Abstract

Wide bandgap (E _g) mixed-halide perovskite has attracted much attention for applications in photovoltaic devices. However, devices featuring this type of perovskite are often subject to a large voltage deficit due to the occurrence of phase segregation, which limits the relevant devices’ access to high performances. Here, the correlation of the phase segregation and voltage losses for wide-E _g mixed-halide perovskite solar cells (PSCs) is clarified by experiments and simulations. Taking 1.67 eV E _g mixed-halide perovskite as an example, it is confirmed experimentally that the control devices produce a poor physical morphology, a locally widened E _g, and an inferior electrical response. By suppressing the phase segregation, the open-circuit voltage (V _oc) can be boosted from 1.15 to 1.20 V, which is a high value for the 1.67 eV E _g mixed-halide PSCs. An electrical simulation of phase segregation reveals that the performance degeneration can be attributed to the bulk recombination due to the energy level mismatch of the varied E _gs. Moreover, a theoretical perspective is produced to expatiate on the strategies for the high V _oc of wide-E _g PSCs. This study brings deep guidance to unlock the potential for high-performance mix-halide PSCs.

4-Aminomethyltetrahydropyran acetate is used as the surface passivation agent for CsPbIBr₂ perovskite, which can passivate the surface defects and form a more beneficial energy level arrangement of CsPbIBr₂ film. These benefits contribute to reduced recombination of carriers inside the corresponding device and yield faster hole extraction. Thereby, the CsPbIBr₂ hole transport layer free carbon-based perovskite solar cells with better photovoltaic performance and long-term stability are fabricated.

Abstract

Inorganic cesium lead halide perovskite solar cells have attracted widespread attention owing to their excellent stability relative to organic–inorganic solar cells. However, all-inorganic perovskite solar cells without hole transport layers and using carbon layers as electrodes have serious energy level mismatch problems. To overcome this problem, here, the CsPbIBr₂ surface is treated with 4-aminomethyltetrahydropyran acetate to form a gradient energy band on the CsPbIBr₂ perovskite/carbon interface. As a result, the hole extraction efficiency is successfully improved, and the morphology and crystallization of the perovskite layer are also improved. Moreover, the nonradiative recombination inside the perovskite and the charge recombination at the interface are effectively inhibited. Therefore, the power conversion efficiency of CsPbIBr₂ solar cell is enhanced to 10.12%, and the high photovoltage of 1.32 V is obtained under one solar illumination, which are both higher than the pristine one (7.79%, 1.23V, respectively).

Publication date: 15 December 2021

Source: Joule, Volume 5, Issue 12

Author(s): Jiang Liu, Erkan Aydin, Jun Yin, Michele De Bastiani, Furkan H. Isikgor, Atteq Ur Rehman, Emre Yengel, Esma Ugur, George T. Harrison, Mingcong Wang, Yajun Gao, Jafar Iqbal Khan, Maxime Babics, Thomas G. Allen, Anand S. Subbiah, Kaichen Zhu, Xiaopeng Zheng, Wenbo Yan, Fuzong Xu, Michael F. Salvador

A mechanochemical route to prepare stoichiometric-pure and air-stable δ-FAPbI₃ powders is developed, which can be stored for more than 10 months in ambient environment. Redissolving the δ-FAPbI₃ powders can generate a high concentration of large-sized polyiodide colloids, which can serve as nuclei to promote heterogeneous nucleation for perovskite films. As a result, a competitive solar cell efficiency of 24.22% is achieved.

Abstract

A prerequisite for commercializing perovskite photovoltaics is to develop a swift and eco-friendly synthesis route, which guarantees the mass production of halide perovskites in the industry. Herein, a green-solvent-assisted mechanochemical strategy is developed for fast synthesizing a stoichiometric δ-phase formamidinium lead iodide (δ-FAPbI₃) powder, which serves as a high-purity precursor for perovskite film deposition with low defects. The presynthesized δ-FAPbI₃ precursor possesses high concentration of micrometer-sized colloids, which are in favor of preferable crystallization by spontaneous nucleation. The resultant perovskite films own preferred crystal orientations of cubic (100) plane, which is beneficial for superior carrier transport compared to that of the films with isotropic crystal orientations using “mixture of PbI₂ and FAI” as precursors. As a result, high-performance perovskite solar cells with a maximum power conversion efficiency of 24.2% are obtained. Moreover, the δ-FAPbI₃ powder shows superior storage stability for more than 10 months in ambient environment (40 ± 10% relative humidity), being conducive to a facile and practical storage for further commercialization.

Highly efficient, thick ternary organic solar cells are fabricated by roll-to-roll (R2R)-compatible slot-die coating via kinetics manipulation. A highly crystalline molecule, BTR-Cl, is incorporated, and the phase-separation kinetics of the D18:Y6 film is regulated. The molecular crystallinity and vertical phase separation of the ternary blends is improved, which results in high power conversion efficiencies of 17.2% and 15.5% for photoactive films with thicknesses of 110 and 300 nm, respectively.

Abstract

Power conversion efficiency (PCE) of organic solar cells (OSCs) has crossed the 18% mark for OSCs, which are largely fabricated by spin-coating, and the optimal photoactive thickness is limited to 100 nm. To increase reproducibility of results with industrial roll-to-roll (R2R) processing, slot-die coating coupled with a ternary strategy for optimal performance of large-area, thick OSCs is used. Based on miscibility differences, a highly crystalline molecule, BTR-Cl, is incorporated, and the phase-separation kinetics of the D18:Y6 film is regulated. BTR-Cl provides an early liquid–liquid phase separation and early aggregation of Y6, which slightly improves the molecular crystallinity and vertical phase separation of the ternary blends, resulting in high PCEs of 17.2% and 15.5% for photoactive films with thicknesses of 110 and 300 nm, respectively. The ternary design strategy for large-area and thick films is further used to fabricate high-efficiency flexible devices, which promises reproducibility of the lab results from slot-die coating to industrial R2R manufacturing.

The buried interface between the perovskite and the electron transport layer is crucial for the further improvement of efficiency and stability of perovskite solar cells. Herein, the SnO₂/perovskite buried interface is enhanced by cesium modification. The CsI-SnO₂ complex facilitates growth of perovskite films and suppresses the carrier recombination. The champion efficiency of modified devices reaches 23.3% with excellent UV stability.

Abstract

The buried interface between the perovskite and the electron transport layer (ETL) plays a vital role for the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). However, it is challenging to efficiently optimize this interface as it is buried in the bottom of the perovskite film. Herein, a buried interface strengthening strategy for constructing efficient and stable PSCs by using CsI-SnO₂ complex as an ETL is reported. The CsI modification facilitates the growth of the perovskite film and effectively passivates the interfacial defects. Meanwhile, the gradient distribution of Cs⁺ contributes to a more suitable band alignment with the perovskite, and the incorporation of Cs⁺ into the perovskite at the bottom interface enhances the resistance against UV illumination. Eventually, a significantly improved PCE up to 23.3% and a much-enhanced UV stability of FAPbI₃-based PSCs are achieved. This work highlights the importance of cesium-enhanced interfaces and provides an effective approach for the simultaneous realization of highly efficient and UV-stable perovskite solar cells.

To modulate the morphology of all-small-molecule organic solar cells, a polymerized small-molecule acceptor PJ1 is introduced into a high-efficiency system ZR-TT: Y6 as an interface modulator. By accelerating hole transfer and enhancing charge transport, the more condensed and uniform morphology contribute to an enhanced power conversion efficiency of 15.54% in 3% PJ1 added devices. This strategy shows good generality.

Abstract

Modulating the morphology of all-small-molecule organic solar cells (ASM-OSCs) has proved to be a considerable challenge in the context of efficient exciton dissociation and charge transport. Regulating the morphology of ASM-OSCs is a great challenge due to the low viscosity of the small molecules, which tend to form large domain sizes and loose molecular packing, especially in the interfacial region. Here, a polymerized small-molecule acceptor (PJ1) is introduced as an interface modulator to strengthen the interfacial molecular interactions in a high-efficiency system, consisting of a novel small molecule donor (ZR-TT) and a widely used acceptor (Y6). Optimized ASM-OSCs exhibit a power conversion efficiency (PCE) of 14.33% without any additives. A small amount of PJ1 effectively condenses the morphology, enhances the crystallinity of the blend, and decreases the domain sizes. Upon 3% PJ1 addition in the blends, the accelerated hole transfer and the enhanced charge transport ultimately lead to an increased PCE of 15.54% with improved short circuit current and fill factor. Notably, the generality of this interfacial modulator strategy is proved by using PJ1 in three other ASM-OSCs and using another polymerized host acceptor, PYT-F-o.

Publication date: February 2022

Source: Nano Energy, Volume 92

Author(s): Fengyou Wang, Xin Li, Jinyue Du, Hui Duan, Haoyan Wang, Yue Gou, Lili Yang, Lin Fan, Jinghai Yang, Federico Rosei

A power-conversion efficiency of 2.51% with short-circuit current density of 28.07 mA cm⁻² is realized for the thin-film solar cell fabricated using a vapor-transport-deposited orthorhombic tin-selenide absorber layer.

The power-conversion efficiencies of orthorhombic tin selenide (α-SnSe)-based thin-film solar cells (TFSCs) are very low—less than 1% in most cases—due to the poor crystallinity, small grains, and large number of defects. Herein, the highest cell efficiency of 2.51% together with a high short-circuit current density of 28.07 mA cm⁻² for α-SnSe TFSCs grown via vapor-transport-deposition (VTD) is reported. The grain size and surface roughness of the SnSe thin films greatly influence the shunt properties of the device. Significantly large shunt losses are detected in the case of both small and extremely large grains. The shunt losses for SnSe thin film with small grains are associated with high grain-boundary scattering. The presence of extremely large grains results in high surface roughness of the SnSe thin film, which causes nonuniform deposition of the CdS buffer layer and, consequently, higher shunt losses. The SnSe thin film with moderate-sized grains and inferior surface roughness exhibits improved shunt properties owing to uniform deposition of the CdS buffer layer and subsequent layers and thereby significant improvement in the device performance. The potential of orthorhombic VTD-SnSe thin films as an emerging cost-effective absorber layer for TFSCs is experimentally demonstrated.

The optoelectronic properties and potential of Cs₂AgBiBr₆ double perovskites with respect to their application in lead-free perovskite solar cells are discussed.

Finding lead-free alternatives remains an important and challenging topic in the field of perovskite solar cells. In this perspective, the potential of Cs₂AgBiBr₆ double perovskites in solar cells is discussed based on reported absorption and emission data. Whereas the material is capable of exceeding and potentially doubling current efficiency values of around 3%, mainly by an optimized solar cell design, industrially relevant devices cannot be fabricated without major changes in the absorption onset. Nevertheless, Cs₂AgBiBr₆ poses various scientific questions and exact recombination and charge transport processes are yet to be unraveled, preparing us for the double perovskite or perovskite-like materials to come.

Incorporation of the pseudo-alkali metal cation dimethylammonium into the Cs-stabilized formamidinium lead triiodide perovskite precursor solution for fabricating the printed perovskite solar cells, achieves crystallization control and grain boundary passivation of the perovskite in the mesoscopic scaffold, yielding a device with a power conversion efficiency of 17.46% and long-term operational stability.

Upscaling efficient and stable perovskite materials is vital for metal halide perovskite solar cells (PSCs) and additive engineering contributes a lot to making high-quality PSCs. While the recent examples involved mixing dimethylammonium (DMA) cation has been employed for the fabrication of all-inorganic perovskites with improved efficiency and stability, the role of DMA cation in hybrid perovskite (formamidinium lead triiodide, denoted as FAPbI₃) remains inconclusive. Herein, DMA cations are substituted for FA sites of Cs_0.12FA_0.88PbI₃ for printable triple mesoscopic PSCs and shed lights on the roles and mechanism of DMA in the perovskite. It is found that a small amount of DMA is doped into the perovskite lattices, meanwhile, an intermediate compound DMAPbI₃ is formed and exists at grain boundaries, which improves the crystallinity of perovskite films and reduces nonradiative recombination through a passivation role. With these benefits, the best-performing printable PSC attained a power conversion efficiency of 17.46%. Unencapsulated devices maintained over 96% of the initial efficiencies in ambient condition for 960 h and 95% of the initial efficiencies after 360 h under continuous thermal aging at 85 °C in N₂ atmosphere.

An innovative quasi-interdigitated back-contact (QIBC) perovskite solar cell (PSC) structure featuring a front-carrier transport layer (FCTL) and a broad back-contact pitch is reported. The optimized QIBC-PSC with CuO FCTL demonstrates the best-modeled efficiency of 23.23%, with over 25% efficiency available.

Interdigitated back-contact (IBC) perovskite solar cells (PSCs) have great potential for highly efficient and low-cost solar energy conversion. However, their full potential has not been achieved. In particular, there is no practically available front surface and rear contact design for IBC-PSCs as for the conventional crystalline silicon IBCs, which propose challenges in realizing high efficiency. Herein, innovative quasi-interdigitated back-contact (QIBC) PSC designs that enhance the effective lateral transport of carriers are proposed and therefore a realistic wide pitch for back contacting in the range of hundreds of micrometers is allowed. The novel design features implementing an appropriate conductive and well-passivated carrier transport layer, referred to as a front-carrier transport layer (FCTL), on the front surface of the QIBC-PSC. Technology computer-aided design optical/device simulations are used to investigate the function of the FCTL in increasing the cell performance and achieve 23.23% of power conversion efficiency (PCE) after FCTL design optimizations for a QIBC-PSC with a rear contact pitch of 200 μm. Further improvement of the PCE over 25% can be potentially achievable by improving the film and passivation quality. This work opens up a new approach to fabricate realistic highly efficient IBC-PSCs.

By inserting a functional polymer polymethyl methacrylate thin layer at the perovskite interface, the hole transfer layer (HTL)/Pb-free carbon-electrode-based Cs₂AgBiBr₆ perovskite solar cell achieves an enhanced power conversion efficiency of 2.25% with a high open-circuit voltage of 1.18 V owing to the reduced defects and suppressed short-circuit-induced shunt loss.

All-inorganic lead-free Cs₂AgBiBr₆ double perovskite solar cells (PSCs) have attracted growing attention owing to their eco-friendly features and robust intrinsic stability. However, arising from the rapid crystal growth, the poor film quality always leads to substantial non-radiative recombination and inferior performance improvement. Herein, high-efficiency and stable Cs₂AgBiBr₆ PSCs are obtained by introducing a functional polymethyl methacrylate (PMMA) layer at the perovskite surface to avoid direct contact between carbon and the underlying charge transfer layer, as well as to passivate the defects. When assembling into solar cells, the non-radiative charge recombination is suppressed and the interfacial charge extraction is accelerated. As a result, the carbon-electrode-based Cs₂AgBiBr₆ PSC yields an enhanced efficiency of 2.25% with a high open-circuit voltage of 1.18 V. Moreover, the unencapsulated device exhibits superior long-term stability owing to the protection of the PMMA layer from corrosion by the extraneous water and oxygen, retaining nearly 100% of the initial efficiency after storage in 25 °C, with 5% relative humidity (RH) for 80 days and high temperature of 85 °C, and 0% RH for 60 days, respectively. A simple method of polymer passivation for enhancing the performance and stability of Pb-free Cs₂AgBiBr₆ PSCs is provided.

2-Bromo-6-fluoronaphthalene (BFN) is employed to stabilize iodine ions in printable hole-conductor-free mesoscopic perovskite solar cells via the halogen bond interaction. Two halogen terminals and the fused ring help tune the energy levels of the perovskite. An efficiency of 16.77% is achieved due to accelerated hole extraction and inhibited charge recombination.

Perovskite solar cells (PSCs) are considered to be the most promising next-generation photovoltaic technology. Among all the configurations of PSCs, the printable hole-conductor-free mesoscopic PSC (p-MPSC) has unique advantages on low cost, large-area fabrication and fabulous stability, which endows it with the greatest potential for industrialization. The interfacial recombination losses, especially at the perovskite/carbon interface, are the bottleneck for further improving the power conversion efficiency (PCE) of p-MPSCs. 2-Bromo-6-fluoronaphthalene is introduced as an interfacial modulator for p-MPSCs through post-treatment. The bromo-terminal acts as an electrophilic site to interact with the iodine ion in perovskite via the noncovalent halogen bond. Meanwhile, the fused ring of naphthalene is capable to accommodate electron density that is attracted from the perovskite. This interaction induces a more favorable band structure at the interface. The hole extraction is promoted and the interfacial nonradiative recombination is inhibited. Accordingly, a champion p-MPSC with an improved PCE of 16.77% from 15.50% of the pristine device is obtained.

The long-lived excitons are of significance to alleviate the strong morphology- and thickness-dependence of organic photovoltaic performance and therefore accelerating its industrialization process. Here, two room-temperature phosphorescent electron acceptors with long-lived triplet exctions and high-energy level are investigated systematically for the first time. This work provides revelatory insights into their fundamental electronic characteristics, photophysical mechanism, and photo-to-current generation pathway.

Abstract

Organic phosphorescence, originating from triplet excitons, has potential for the development of new generation of organic optoelectronic materials. Herein, two heavy-atom-free room-temperature phosphorescent (RTP) electron acceptors with inherent long lifetime triplet exctions are first reported. These two 3D-fully conjugated rigid perylene imide (PDI) multimers, as the best nonfullerene wide-bandgap electron acceptors, exhibit a significantly elevated T₁ of ≈2.1 eV with a room-temperature phosphorescent emission (τ = 66 µs) and a minimized singlet–triplet splitting as low as ≈0.13 eV. The huge spatial congestion between adjacent PDI skeleton endows them with significantly modified electronic characteristics of S₁ and T₁. This feature, plus with the fully-conjugated rigid molecular configuration, balances the intersystem crossing rate and fluorescence/phosphorescence rates, and therefore, elevating E _T1 to ≈2.1 from 1.2 eV for PDI monomer. Meanwhile, the highly delocalized feature enables the triplet charge-transfer excitons at donor–acceptor interface effectively dissociate into free charges, endowing the RTP electron acceptor based organic solar cells (OSCs) with a high internal quantum efficiency of 84% and excellent charge collection capability of 94%. This study introduces an alternative strategy for designing PDI derivatives with high-triplet state-energy and provides revelatory insights into the fundamental electronic characteristics, photophysical mechanism, and photo-to-current generation pathway.

Various diammonium spacer cations are used to construct 2D/3D perovskite. The mechanism of molecular configuration-induced regulation of crystal orientation and carrier dynamics is investigated. 2D/3D perovskite solar cells based on 2,2′-(ethylenedioxy)bis(ethylamine) achieve a device efficiency of 22.68 % and excellent moisture stability, retaining 82 % of initial efficiency after aging at 50±5 % relative humidity for 1560 h.

Abstract

The effects from the molecular configuration of diammonium spacer cations on 2D/3D perovskite properties are still unclear. Here, we investigated systematically the mechanism of molecular configuration-induced regulation of crystallization kinetic and carrier dynamics by employing various diammonium molecules to construct Dion-Jacobson (DJ)-type 2D/3D perovskites to further facilitating the photovoltaic performance. The minimum average Pb-I-Pb angle leads to the smallest octahedral tilting of [PbX₆]⁴⁻ lattice in optimal diammonium molecule-incorporated DJ-type 2D/3D perovskite, which enables suitable binding energy and hydrogen-bonding between spacer cations and inorganic [PbX₆]⁴⁻ cages, thus contributing to the formation of high-quality perovskite film with vertical crystal orientation, mitigatory lattice distortion and efficient carrier transportation. As a consequence, a dramatically improved device efficiency of 22.68 % is achieved with excellent moisture stability.

Organic solar cell active layers with A-DAD-A (A = acceptor; D = donor) non-fullerene acceptors (NFAs) having different extents of end group fluorination are systematically characterized in terms of film crystallinity, donor-acceptor depth distribution, charge carrier transport, and cell performance. The most fluorinated NFA, BT-BO-L4F, has optimal hierarchical morphology and vertical phase gradation, affording a power conversion efficiency of 16.81%.

Abstract

Non-fullerene acceptor (NFA) end group (EG) functionalization, especially by fluorination, affects not only the energetics but also the morphology of bulk-heterojunction (BHJ) organic solar cell (OSC) active layers, thereby influencing the power conversion efficiency (PCE) and other metrics of NFA-based OSCs. However, a quantitative understanding of how varying the degrees of NFA fluorination influence the blend morphological and photovoltaic properties remains elusive. Here a series of three A-DAD-A type NFAs (D = π-donor group and A = π-acceptor EG) which systematically increase the degree of EG fluorination and comprehensively investigate the resulting blends with the polymer donor PM6 in terms of optical properties, electronic structure, film crystallinity, charge carrier transport, and OSC performance is reported. The results indicate that the most highly fluorinated NFA, BT-BO-L4F, achieves an optimal BHJ hierarchical morphology where enhanced NFA molecule intermolecular π–π stacking and optimal vertical phase gradation are achieved in the BHJ blend. These factors also promote optimum NFA-cathode contact, more balanced electron and hole mobility, and suppress both monomolecular and bimolecular recombination. As a result, both the short-circuit current density and fill factor in this OSC series progressively increase with increasing EG fluorine density, and the resulting PCEs increase from 9 to 16.8%.

Non-Fullerene Acceptors

In article number 2102363, Denis Andrienko and co-workers summarize the chemical design rules of non-fullerene acceptor molecules for use in efficient organic solar cells. In particular, they propose that the energy level bending that promotes the generation of free charges requires a planar acceptor–donor–acceptor molecular architecture, and molecular alignment parallel to the interface. These design rules are benchmarked against existing non-fullerene acceptors and are used to pre-screen a set of molecular building blocks for new acceptors with potentially high power conversion efficiencies.

In addition to the molecular design of the backbone, side chain engineering is another fundamental method for polymer modification. A benzo[1,2-b:4,5-b′]dithiophene (BDT)-benzodithiophene-4,8-dione copolymer PBDB-Cz is developed by employing carbazole as the conjugated side chain of BDT, which exhibits outstanding superior hole transport properties over its thiophene and alkoxy counterparts when used in n–i–p perovskite solar cells.

Abstract

In conventional n–i–p perovskite solar cells (PVSCs), electron donor (D)–acceptor (A) polymers have been found to be potential substitutes for doped spiro-based small molecule hole-transporting materials (HTMs) due to their excellent performance in hole mobility, film formability, and stability. Herein, a benzo[1,2-b:4,5-b′]dithiophene (BDT)-benzodithiophene-4,8-dione (BDD) copolymer PBDB-Cz is developed by employing carbazole as the conjugated side chain of BDT. PBDB-O and PBDB-T with alkoxy and thiophene as the side chain of BDT, respectively, are also synthesized and studied for comparison. The synergistic effect of the carbazole side chain and the BDT-BDD backbone to promote hole transport properties is found in PBDB-Cz. The carbazole side chain enhances both coplanarity and interaction of polymer chains, while simultaneously deepening energy levels and improving the hole mobility of the polymeric HTM. Consequently, PBDB-Cz outperforms two counterparts, exhibiting a promising power conversion efficiency (PCE) of 22.06%. Notably, the PBDB-Cz also improves the device stability, and the devices can retain more than 90% of their initial PCEs after being stored at ambient conditions for 100 days. To the best of the authors’ knowledge, this is the first report to incorporate carbazole into D–A polymeric HTM by side chain engineering.

A novel and low-cost phenothiazine-based self-assembly monolayer is designed and employed at the hole-transporting layer in a p-i-n perovskite solar cell, yielding a high efficiency over 22% along with an impressive operational stability over 100 h. This feature mainly originates from its well-aligned energy level match with the perovskite and efficient interfacial defect passivation.

Abstract

Recent advances in perovskite solar cells (PSCs) performance have been closely related to improved interfacial engineering and charge selective contacts. Here, a novel and cost-competitive phenothiazine based, self-assembled monolayer (SAM) as a hole-selective contact for p-i-n PSCs is introduced. The molecularly tailored SAM enables an energetically well-aligned interface with the perovskite absorber, with minimized nonradiative interfacial recombination loss, thus dramatically improving charge extraction/transport and device performance. The resulting PSCs exhibit a power conversion efficiency (PCE) of up to 22.44% (certified 21.81%) with an average fill factor close to 81%, which is among the highest efficiencies reported to date for p-i-n PSCs. The new SAM also demonstrates the outstanding operational stability of the PSC, with increasing PCE from 20.3% to 21.8% during continuous maximum power point tracking under a simulated 1 sun illumination for 100 h. The reported findings highlight the great potential of engineered SAMs for the fabrication of stable and high performing PSCs.

A series of polymer acceptors with controlled backbone regioregularities and side-chain structures is developed. All-polymer solar cells based on regioregular-C20 acceptor having a regioregular backbone and optimal side chain length achieve a high power conversion efficiency of 15.12%, attributed to high electron mobility and optimal blend morphology.

Abstract

Tuning the aggregation and crystalline properties of polymers is critical for realizing all-polymer solar cells (all-PSCs) with optimal blend morphology and high power conversion efficiency (PCE). In this study, a series of polymerized small-molecule acceptors (PSMAs) is developed to investigate important relationships among their crystalline/aggregation properties, the blend morphology, and the device performance of the resulting all-PSCs. A series of PSMAs (regiorandom (RRd)-C12, RRd-C20, RRd-C24, regioregular (RRg)-C20, and RRg-C24) with simultaneously-engineered i) side chain lengths of C12, C20, and C24, and ii) backbone regioregularities of RRd and RRg are synthesized to regulate their crystalline/aggregation properties. As a result, the highest PCE of 15.12% is obtained with all-PSCs based on RRg-C20 PSMA having regioregular backbone and optimal side chain length, attributed to high PSMA crystallinity and electron mobility as well as optimal blend morphology with a polymer donor. Thus, this study demonstrates the importance of simultaneous engineering of the backbone regioregularity and side-chain structures of PSMAs to enhance electron mobility, optimize blend morphology and, thus, achieve highly efficient all-PSCs.

The quality of buried interfaces in inverted perovskite solar cells is improved via constructing hole-transporting materials with deep HOMO levels, high wetting, and passivation capabilities. By systematically regulating the linking-site of pyridine unit, high efficiencies exceeding 22% (0.09 cm²) and 20% (1 cm²) are achieved.

Abstract

Inverted-structured perovskite solar cells (PSCs) mostly employ poly-triarylamines (PTAAs) as hole-transporting materials (HTMs), which generally result in low-quality buried interface due to their hydrophobic nature, shallow HOMO levels, and absence of passivation groups. Herein, the authors molecularly engineer the structure of PTAA via removing alkyl groups and incorporating a multifunctional pyridine unit, which not only regulates energy levels and surface wettability, but also passivates interfacial trap-states, thus addressing above-mentioned issues simultaneously. By altering the linking-site on pyridine unit from ortho- (o-PY) to meta- (m-PY) and para-position (p-PY), they observed a gradually improved hydrophilicity and passivation efficacy, mainly owing to increased exposure of the pyridine-nitrogen as well as its lone electron pair, which enhances the contact and interactions with perovskite. The open-circuit voltage and power conversion efficiency (PCE) of inverted-structured PSCs based on these HTMs increased with the same trend. Consequently, the optimal p-PY as HTM enables facile deposition of uniform perovskite films without complicated interlayer optimizations, delivering a remarkably high PCE exceeding 22% (0.09 cm²). Moreover, when enlarging device area tenfold, a comparable PCE of over 20% (1 cm²) can be obtained. These results are among the highest efficiencies for inverted PSCs, demonstrating the high potential of p-PY for future applications.

Controlling grain growth and passivating defects are essentially important for improving the photovoltaic performance of antimony selenide (Sb₂Se₃) thin-film solar cells. In this study, the seed-layer templated growth and post-air annealing is combined to prepare vertically oriented and passivated Sb₂Se₃ films on molybdenum substrates. As a result, substrate configuration Sb₂Se3 solar cells with a champion efficiency of 8.5% are demonstrated.

Abstract

Antimony selenide (Sb₂Se₃) is a promising low-cost photovoltaic material with a 1D crystal structure. The grain orientation and defect passivation play a critical role in determining the performance of polycrystalline Sb₂Se₃ thin-film solar cells. Here, a seed layer is introduced on a molybdenum (Mo) substrate to template the growth of a vertically oriented, columnar Sb₂Se₃ absorber layer by closed space sublimation. By controlling the grain orientation and compactness of the Sb₂Se₃ seeds, obtain high-quality Sb₂Se₃ absorber layers with passive Sb₂Se₃/Mo interfaces is obtained, which in turn improve the transport of photoexcited charge carriers through the absorber layer and its interfaces. Post-deposition annealing of absorber layers in ambient air is further utilized to passivate the defects in Sb₂Se₃ and enhance the quality of the front heterojunction. As a result of systematic processing optimization, Sb₂Se₃ planar heterojunction solar cells are fabricated in substrate configuration with a champion power conversion efficiency of 8.5%.

The combined results from solid-state NMR, crystallography, and modelling techniques highlight key differences in the Y6 morphology in PM6:Y6 blends cast from different solvents, which lead to different power conversion efficiencies in solar cells. By interpreting the experimental data step-by-step and using the results from each step, a more complete understanding of the underlying fundamental processes is reached.

Abstract

Fused-ring core nonfullerene acceptors (NFAs), designated “Y-series,” have enabled high-performance organic solar cells (OSCs) achieving over 18% power conversion efficiency (PCE). Since the introduction of these NFAs, much effort has been expended to understand the reasons for their exceptional performance. While several studies have identified key optoelectronic properties that govern high PCEs, little is known about the molecular level origins of large variations in performance, spanning from 5% to 18% PCE, for example, in the case of PM6:Y6 OSCs. Here, a combined solid-state NMR, crystallography, and molecular modeling approach to elucidate the atomic-scale interactions in Y6 crystals, thin films, and PM6:Y6 bulk heterojunction (BHJ) blends is introduced. It is shown that the Y6 morphologies in BHJ blends are not governed by the morphology in neat films or single crystals. Notably, PM6:Y6 blends processed from different solvents self-assemble into different structures and morphologies, whereby the relative orientations of the sidechains and end groups of the Y6 molecules to their fused-ring cores play a crucial role in determining the resulting morphology and overall performance of the solar cells. The molecular-level understanding of BHJs enabled by this approach will guide the engineering of next-generation NFAs for stable and efficient OSCs.

New polymer acceptors (P_As) are developed by embedding flexible conjugation-break spacer (FCBS) units into the rigid backbones. The incorporation of FCBS affords effective modulation of the crystallinity and pre-aggregation of the P_A and attains optimal blend morphology. As a result, the all-polymer solar cells exhibit both a high efficiency of 14.68% and excellent mechanical robustness with a crack onset strain of 21.64%.

Abstract

High efficiency and mechanical robustness are both crucial for the practical applications of all-polymer solar cells (all-PSCs) in stretchable and wearable electronics. In this regard, a series of new polymer acceptors (P_As) is reported by incorporating a flexible conjugation-break spacer (FCBS) to achieve highly efficient and mechanically robust all-PSCs. Incorporation of FCBS affords the effective modulation of the crystallinity and pre-aggregation of the P_As, and achieves the optimal blend morphology with polymer donor (P_D), increasing both the photovoltaic and mechanical properties of all-PSCs. In particular, an all-PSC based on PYTS-0.3 P_A incorporated with 30% FCBS and PBDB-T P_D demonstrates a high power conversion efficiency (PCE) of 14.68% and excellent mechanical stretchability with a crack onset strain (COS) of 21.64% and toughness of 3.86 MJ m^-3, which is significantly superior to those of devices with the P_A without the FCBS (PYTS-0.0, PCE = 13.01%, and toughness = 2.70 MJ m^-3). To date, this COS is the highest value reported for PSCs with PCEs of over 8% without any insulating additives. These results reveal that the introduction of FCBS into the conjugated backbone is a highly feasible strategy to simultaneously improve the PCE and stretchability of PSCs.