The inferior fill factor (FF) is one of main reasons impeding further improvement of power conversion efficiencies (PCEs) in organic solar cells (OSCs). But no theoretical framework for high FFs has been established yet. Herein, an efficient strategy is developed to enhance FFs via introducing a small molecule, CNDT, into active layer to increase electron donor/acceptor interface disorder, raise energy barrier for charge back transfer, and thus reduce bimolecular recombination rate constant (krec). CNDTs tend to distribute over donor/acceptor interfaces and disturb molecular stacking of Y6 to deliver more disordered donor/acceptor interfaces but higher crystal quality in the D18:Y6+ blend film, compared to D18:Y6. Altogether, in the D18:Y6+ blend film, a higher energy of charge transfer state magnifies energy barrier for charge recombination to decrease charge recombination rate/ratio and reduce krec, inhibiting bimolecular recombination in devices. Therefore, FFs of OSCs are improved from 75.78% (D18:Y6) to 81.13% (D18:Y6+), yielding a higher PCE of 19.45%. Moreover, D18:L8-BO+ based OSCs feature FFs over 83%, a record for OSCs so far. PCE increases subsequently to 19.80%. It demonstrates that increasing interface disorder without sacrificing crystal quality enhances energy barrier of charge recombination and inhibits bimolecular recombination to efficiently improve FFs for higher PCEs.

In this work, we propose a novel strategy of introducing luminescent acridine units for central nuclear substitution in quinoxaline-based acceptor molecules (named AQx-o-Ac and AQx-m-Ac) to enhance their photoluminescence quantum yields (PLQY), which can effectively improve the electroluminescent quantum efficiency (EQEEL) of OSCs and thereby suppress Delta Enr. In addition, the substituted acridine unit accelerates molecular aggregation and optimizes molecular crystallization, effectively alleviating the static disorder of acceptor molecules and facilitating charge extraction and transport in OSCs. As a result, the PM6:AQx-m-Ac binary OSCs achieve an excellent PCE of 18.64% with an exceptionally low Delta Enr of 0.166 eV. To the best of our knowledge, a Delta Enr of 0.166 eV represents the lowest value reported for OSCs achieving PCEs over 18 %. Finally, the acceptor AQx-m-Ac is incorporated into PM6:eC9 blend as the third component, and the optimal ternary device produces a superior PCE of 20.28%. This work highlights the potential of promoting luminescence for suppressing nonradiative energy loss and charts a viable path for upcoming breakthrough in high-efficiency organic photovoltaics.

Organic solar cells (OSCs) have shown great applications potential in flexible/wearable electronics, indoor photovoltaics and so on. The efficiencies of single-junction OSCs have exceeded 19%, making the commercialization of OSCs brighter. Large-area printing fabrication is a key way to the commercialization of OSCs, and solution-processed thickness-insensitive cathode interlayers (CILs) are urgently needed for large-area printing fabrication. High electron mobility of cathode interfacial materials (CIMs) is critical to enable thickness-insensitive CILs. N-type self-doped characteristics can endow organic CIMs with high electron mobility. Different type of n-type self-doped CIMs show different applicability in conventional OSCs and inverted OSCs. External n-type dopants can further increase electron mobility of hybrid blends. Particularly, ZnO doped with organic dyes can achieve superior photoconductivity in inverted OSCs. This review focuses on solution-processed thickness-insensitive CILs for high-performance OSCs. In conventional OSCs, n-type self-doped small molecules and polymers, and external n-doped hybrid blends as thickness-insensitive CILs are summarized. In inverted OSCs, n-type self-doped small-molecular electrolytes and polyelectrolytes, PEI-/PEIE-based polyelectrolytes, and external n-doped hybrid blends (including organic-organic and ZnO-organic) are summarized for thickness-insensitive CILs. The relationships between particular functions of CILs and chemical structures of CIMs are highlighted. Finally, summary and outlook of solution-processed thickness-insensitive CILs are provided.

Reducing the single-triplet energy gap (triangle E-ST) for organic photovoltaic (OPV) molecules has been proposed to be able to reduce the nonradiative recombination by tuning the low-lying triplet state (T-1) and/or the excited state (S-1), thus reducing the energy loss (E-loss) and increasing the open-circuit voltage in their devices. However, how to design the non-fullerene acceptor (NFA) with small triangle E-ST and high performance is challenging. Aiming to address this issue, YDF, YTF, and YTF-H were synthesized. Among them, a device based on YDF with partially spatially separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) exhibits a much higher power conversion efficiency (PCE) of 20.04%, which is one of the most efficient efficiencies for binary systems. For YTF and YTF-H, their completely spatially separated HOMO and LUMO indeed lead to a much reduced triangle E-ST caused by the low-lying S-1 state, together with excellent charge mobility and light absorption, required for higher performance OPV. But their low S-1 state causes several non-radiative recombinations due to strong S-1-S-0 coupling (PCE < 1.5%). These results indicate that future designs to have high performance molecules with small triangle E-ST should avoid the sharp decrease in S-1, and the ideal scenario would be to elevate the T-1 state, thereby mitigating the energy gap law.

Interfacial engineering is a proven strategy to enhance the efficiency of perovskite solar cells (PeSCs) by controlling surface electronic defects and carrier trapping. The trap states at the "top" interface between the perovskite and upper charge extraction layers are experimentally accessible and have been extensively studied. However, the understanding of the unexposed "bottom" surface of the perovskite layer remains elusive, due to the lack of selective and non-destructive tools to access buried interface. Here, a new spectroscopy technique is introduced that monitors nanosecond to millisecond dynamics of trapped carriers at the buried interfaces by combining optical trap activation by infrared light with surface photovoltage detection. Applied to various PeSC architectures, this method reveals that most interfacial traps reside between the perovskite and hole transport layer, suggesting a predominance of hole traps (e.g., cation and lead vacancies) over electron traps (e.g., halide vacancies) in the studied PeSC systems. The proposed new approach separates interfacial carrier-loss contributions from the top and buried surfaces, providing design insights for achieving high-performance PeSCs through interface optimization.

Cellulose-based materials can be classified as non-conventional luminogens that produce photoluminescence (PL) in the visible range due to specific intermolecular arrangements. Usually such an arrangement is referred to as clusterization. Here, we demonstrate the importance of intramolecular arrangement of ethyl cellulose and bacterial cellulose that demonstrate tunable photoluminescence with multiexponent decay. We show that the observed emission is due to a n-pi* electronic transition of carbonyl groups, whose emission intensity depends on the form of the sample preparation, either the powder-form or spin-coated films, displaying different density of the emitting regions on the microscale. Particularly, it is shown that PL emission is produced from disordered amorphous regions rather than from crystalline ones. We show that the emission is also promoted by mechanical stress applied to the sample that is suggested to facilitate formation of hydrogen-bonded carbonyl groups. The observed stress-assisted emission opens up the potential perspective of using this phenomenon in printed photonic devices.

Perovskite light-emitting diodes (PeLEDs) are advancing to become the frontrunner candidates for the next generation of lighting and display technologies. However, despite rapid technical development, a thorough understanding of PeLEDs’ environmental and economic impacts—essential information for future commercialization—is currently lacking. Here we assess the environmental and economic performance of 18 representative PeLEDs, aiming to identify effective industrial techniques to develop sustainable PeLEDs from a life-cycle perspective. We find that, like mature organic LEDs, PeLEDs show excellent environmental performance. In addition, we demonstrate that lead is not a major source of toxicity from PeLEDs. We estimate that, to commercialize PeLEDs and improve their sustainability, their lifetime should reach the order of 10,000 hours to compensate for the relative environmental impacts. The techno-economic assessment indicates that the cost of future PeLEDs will probably be in the vicinity of US$100 m–2, comparable to that of commercial organic LED panels. Overall, this study shows the potential of PeLEDs as next-generation lighting technology from environmental, economic and technical perspectives, providing insights relevant to their future development.

Current display screens are typically only used for information display, but can have a range of different sensors integrated into them for functions such as touch control, ambient light sensing and fingerprint sensing. Photo-responsive light-emitting diodes (LEDs), which can display information and respond to light excitation, could be used to develop future ultra-thin and large screen-to-body ratio screens. However, photo-response is difficult to achieve with conventional display technologies. Here, we report a multifunctional display that uses photo-responsive metal halide perovskite LEDs as pixels. The perovskite LED display can be simultaneously used as a touch screen, ambient light sensor and image sensor (including for fingerprint drawing) without integrating any additional sensors. The light-to-electricity conversion efficiency of the pixels also allow the display to act as a photovoltaic device that can charge the equipment. Photo-responsive metal halide perovskite light-emitting diodes can be used to create a multifunctional display that can function as a touch screen, ambient light sensor and image sensor.

Tunable bandgaps make halide perovskites promising candidates for developing tandem solar cells (TSCs), a strategy to break the radiative limit of 33.7% for single-junction solar cells. Combining perovskites with market-dominant crystalline silicon (c-Si) is particularly attractive; simple estimates based on the bandgap matching indicate that the efficiency limit in such tandem device is as high as 46%. However, state-of-the-art perovskite/c-Si TSCs only achieve an efficiency of similar to 32.5%, implying significant challenges and also rich opportunities. In this review, we start with the operating mechanism and efficiency limit of TSCs, followed by systematical discussions on wide-bandgap perovskite front cells, interface selective contacts, and electrical interconnection layer, as well as photon management for highly efficient perovskite/c-Si TSCs. We highlight the challenges in this field and provide our understanding of future research directions toward highly efficient and stable large-scale wide-bandgap perovskite front cells for the commercialization of perovskite/c-Si TSCs.

As the core component of sandwich-like perovskite solar cells (PSCs), the quality of perovskite layer is a challenge for further progress in PSCs due to the unfavorable defects and uncontrollable crystallization. Here, a surface post-treatment strategy employing ethyl thioglycolate (ET) as ligand molecule is developed for property manipulation of perovskite films. ET can lower surface energy of perovskite facets and induces secondary growth of grains, giving films with higher crystallinity and lower defect density. Meanwhile, both carbonyl and sulfhydryl in ET can bind to the Pb2+, thus forming bidentate anchoring on the surface for defect passivation. Besides, the perovskite/ET/C60 interface presents improved charge transfer owing to the well-aligned energy levels. Consequently, the power-conversion-efficiency (PCE) is boosted to 22.42% and 23.56% (certified 23.29%) for the FA0.85Cs0.15Pb(I0.95Br0.05)3 and FA0.9MA0.05Cs0.05Pb(I0.95Br0.05)3 PSCs, respectively, and the FA0.85Cs0.15Pb(I0.95Br0.05)3-based PSC with a larger area (1.03 cm2) delivers a PCE of 20.01%. Importantly, ET demonstrates effective management of I2 and PbI2, thereby preventing accelerated degradation and lead leakage of devices. Thanks to the multiple effects of ET, the resulting devices exhibit significantly enhanced ambient stability over a course of 800 h, and a thermal stability of over 1500 h while maintaining 80.4% of its original efficiency. The efficient and stable inverted perovskite solar cells are developed by introducing ethyl thioglycolate for synergistic crystallization modulation, surface passivation and interfacial PbI2/I2 management. image