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Optoelectronic synaptic transistors are attractive for applications in next-generation brain-like computation systems, especially for their visible-light operation and in-sensor computing capabilities. However, from a material perspective, it is difficult to build a device that meets expectations in terms of both its functions and power consumption, prompting the call for greater innovation in materials and device construction. In this study, we innovatively combined a novel perovskite carrier supply layer with an Al/MoO 3 interface carrier regulatory layer to fabricate optoelectronic synaptic devices, namely Al/MoO 3 /CsFAMA/ITO transistors. The device could mimic a variety of biological synaptic functions and required ultralow-power consumption during operation with an ultrafast speed of >0.1 μs under an optical stimulus of about 3 fJ, which is equivalent to biological synapses. Moreover, Pavlovian conditioning and visual perception tasks could be implemented using the spike-number-dependent plasticity (SNDP) and spike-rate-dependent plasticity (SRDP). This study suggests that the proposed CsFAMA synapse with an Al/MoO 3 interface has the potential for ultralow-power neuromorphic information processing., Competing Interests: The authors declare no conflicts of interest., (This journal is © The Royal Society of Chemistry.)

The perovskite solar cells (PSCs) have achieved great success in power conversion efficiency due to their excellent optoelectrical properties of perovskite. However, the instability of PSCs severely impedes their commercialization. Recently, in situ cross-linking strategy has been proposed to mitigate stability issues of PSCs, enabling highly efficient and stable PSCs. Here, the critical factors that lead to the degradation of PSCs are first outlined. Then, a comprehensive review of in situ cross-linking strategy in perovskite to enhance the moisture, thermal, illumination, and bending stress resistance properties of PSCs is presented. Furthermore, the detailed mechanism underlying these advantageous effects is discussed pertaining to crystallization regulation, immobilization of ions, water resistance, and release of unfavorable stress. Finally, the current challenges and further development trends of in situ cross-linking strategy in PSCs and extension to other optoelectronic devices are prospected., (© 2023 Wiley-VCH GmbH.)

Perovskite single-crystal redissolution (PSCR) strategy is highly desired for efficient formamidinium lead triiodide (FAPbI 3 ) perovskite photovoltaics with enhanced phase purity, improved film quality, low trap-state density, and good stability. However, the phase transition and crystallization dynamics of FAPbI 3 remain unclear in the PSCR process compared to the conventional fabrication from the mixing of precursor materials. In this work, a green-solvent-assisted (GSA) method is employed to synthesize centimeter-sized α-FAPbI 3 single crystals, which serve as the high-purity precursor to fabricate perovskite films. The α-FAPbI 3 PSCR strategy facilitates direct α-phase formation and inhibits the complex intermediate phases monitored by in situ grazing-incidence wide-angle X-ray scattering. Moreover, the α-phase stability is prolonged due to the relaxation of the residual lattice strain through the isotropic orientation phase growth. Consequently, the GSA-assisted PSCR strategy effectively promotes crystallization and suppresses non-radiative recombination in perovskite solar cells, which boosts the device efficiency from 22.08% to 23.92% with significantly enhanced open circuit voltage. These findings provide deeper insight into the PSCR process in terms of its efficacy in phase formation and lattice strain release. The green low-cost solvent may also offer a new and ideal solvent candidate for large-scale production of perovskite photovoltaics., (© 2023 Wiley-VCH GmbH.)

Realization of remote wearable health monitoring (RWHM) technology for the flexible photodiodes is highly desirable in remote-sensing healthcare systems used in space stations, oceans, and forecasting warning, which demands high external quantum efficiency (EQE) and detectivity in NIR region. Traditional inorganic photodetectors (PDs) are mechanically rigid and expensive while the widely reported solution-processed mixed tin-lead (MSP) perovskite photodetectors (PPDs) exhibit a trade-off between EQE and detectivity in the NIR region. Herein, a novel functional passivating antioxidant (FPA) strategy has been introduced for the first time to simultaneously improve crystallization, restrain Sn 2+ oxidization, and reduce defects in MSP perovskite films by multiple interactions between thiophene-2-carbohydrazide (TAH) molecules and cations/anions in MSP perovskite. The resultant solution-processed rigid mixed Sn-Pb PPD simultaneously achieves high EQE (75.4% at 840 nm), detectivity (1.8 × 10 12 Jones at 840 nm), ultrafast response time (t rise /t fall = 94 ns/97 ns), and improved stability. This work also highlights the demonstration of the first flexible photodiode using MSP perovskite and FPA strategy with remarkably high EQE (75% at 840 nm), and operational stability. Most importantly, the RWHM is implemented for the first time in the PIN MSP perovskite photodiodes to remotely monitor the heart rate of humans at rest and after-run conditions., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

It is essential to release annealing induced strain during the crystallization process to realize efficient and stable perovskite solar cells (PSCs), which does not seem achievable using the conventional annealing process. Here we report a novel and facile thermal gradient assisted crystallization strategy by simply introducing a slant angle between the preheated hot plate and the substrate. A distinct crystallization sequence resulted along the in-plane direction pointing from the hot side to the cool side, which effectively reduced the crystallization rate, controlled the perovskite grain growth, and released the in-plane tensile strain. Moreover, this strategy enabled uniform strain distribution in the vertical direction and assisted in reducing the defects and aligning the energy bands. The corresponding device demonstrated champion power conversion efficiencies (PCEs) of 23.70% and 21.04% on the rigid and flexible substrates, respectively. These highly stable rigid devices retained 97% of the initial PCE after 1097 h of storage and more than 80% of the initial PCE after 1000 h of continuous operation at the maximum power point. This novel strategy opens a simple and effective avenue to improve the quality of perovskite films and photovoltaic devices via strain modulation and defect passivation.

The photovoltaic performance of perovskite solar cell is determined by multiple interrelated factors, such as perovskite compositions, electronic properties of each transport layer and fabrication parameters, which makes it rather challenging for optimization of device performances and discovery of underlying mechanisms. Here, we propose and realize a novel machine learning approach based on forward-reverse framework to establish the relationship between key parameters and photovoltaic performance in high-profile MASn x Pb 1-x I 3 perovskite materials. The proposed method establishes the asymmetrically bowing relationship between band gap and Sn composition, which is precisely verified by our experiments. Based on the analysis of structural evolution and SHAP library, the rapid-change region and low-bandgap plateau region for small and large Sn composition are explained, respectively. By establishing the models for photovoltaic parameters of working photovoltaic devices, the deviation of short-circuit current and open-circuit voltage with band gap in defective-zone and low-bandgap-plateau regions from Shockley-Queisser theory is captured by our models, and the former is due to the deep-level traps formed by crystallographic distortion and the latter is due to the enhanced susceptibility by increased Sn 4+ content. The more difficulty for hole extraction than electron is also concluded in the models and the prediction curve of power conversion efficiency is in a good agreement with Shockley-Queisser limit. With the help of search and optimization algorithms, an optimized Sn:Pb composition ratio near 0.6 is finally obtained for high-performance perovskite solar cells, then verified by our experiments. Our constructive method could also be applicable to other material optimization and efficient device development., (© 2022. The Author(s).)

Organic-inorganic hybrid semiconducting (OIHS) materials, which can detect broader spectral regions, are highly desired in several applications including biomedical imaging, night vision, and optical communications. Although lead (Pb)-halide perovskites have reached a mature research stage, high toxicity of Pb hinders their large-scale viability. Tin (Sn)-based perovskites are the most common OIHS broadband light absorbers that replace toxic Pb; however, they are extremely unstable due to the notorious Sn 2+ oxidation. Herein, a novel, non-toxic, and solution-processed millimeter-sized OIHS single crystal [Ga(C 3 H 7 NO) 6 ](I 3 ) 3 has been grown at room temperature. Both the absorption measurement and density functional theory calculations have confirmed a narrow indirect band gap of 1.32 eV. The corresponding photodetector based on this single crystal demonstrated excellent performance including an ultraviolet-visible-near infrared (UV-vis-NIR) response between 325 and 1064 nm, fast response time ( t rise / t decay = 3.8 ms/5.4 ms), and profound air storage stability (41 h), thus outperforming most common photodetectors based on Sn-based perovskites. This work not only provides a profound understanding of this novel organic-inorganic single-crystal material but also demonstrates its great potential to realize the high-performance UV-vis-NIR broadband photodetectors.

A deficiency in the photoelectrical dynamics at the interface due to the surface traps of the TiO 2 electron transport layer (ETL) has been the critical factor for the inferiority of the power conversion efficiency (PCE) in the perovskite solar cells. Despite its excellent energy level alignment with most perovskite materials, its large density of surface defect as a result of sub lattice vacancies has been the critical hurdle for an efficient photovoltaic process in the device. Here, we report that atoms thick 2D TiS 2 layer grown on the surface of a (001) faceted and single-crystalline TiO 2 nanograss (NG) ETL have effectively passivated the defects, boosting the charge extractability, carrier mobility, external quantum efficiency, and the device stability. These properties allow the perovskite solar cells (PSCs) to produce a PCE as high as 18.73% with short-circuit current density ( J sc ), open-circuit voltage ( V oc ), and fill-factor (FF) values as high as 22.04 mA/cm 2 , 1.13 V, and 0.752, respectively, a 3.3% improvement from the pristine TiO 2 -NG-based PSCs. The present approach should find an extensive application for controlling the photoelectrical dynamic deficiency in perovskite solar cells.