Methylammonium Iodide-Mediated Controlled Crystal Growth of CsPbI2Br Films for Efficient and Stable All-Inorganic Perovskite Solar Cells

Low-Power Perovskite Neuromorphic Synapse with Enhanced Photon Efficiency for Directional Motion Perception

The advancement of artificial intelligent vision systems heavily relies on the development of fast and accurate optical imaging detection, identification, and tracking. Framed by restricted response speeds and low computational efficiency, traditional optoelectronic information devices are facing challenges in real-time optical imaging tasks and their ability to efficiently process complex visual data. To address the limitations of current optoelectronic information devices, this study introduces a novel photomemristor utilizing halide perovskite thin films. The fabrication process involves adjusting the iodide proportion to enhance the quality of the halide perovskite films and minimize the dark current. The photomemristor exhibits a high external quantum efficiency of over 85%, which leads to a low energy consumption of 0.6 nJ. The spike timing-dependent plasticity characteristics of the device are leveraged to construct a spiking neural network and achieve a 99.1% accuracy rate of directional perception for moving objects. The notable results offer a promising hardware solution for efficient optoneuromorphic and edge computing applications.

Mechanistic insights into the key role of methylammonium iodide in the stability of perovskite materials

The possible mechanisms damaging perovskite solar cells have attracted considerable attention in the photovoltaic community. This study answers specifically open problems regarding the critical role of methylammonium iodide (MAI) in investigations as well as stabilizing the perovskite cells. Surprisingly, we found that when the molar ratio between PbI₂ : MAI precursor solution increased from 1 : 5 to 1 : 25, the stability of perovskite cells dramatically increased over time. The stability of perovskite in the air without any masking in the average stoichiometry was about five days, while when the amount of MAI precursor solution increased to 5, the perovskite film was unchanged for about 13 days; eventually, when the value of MAI precursor solution enhanced to 25, the perovskite film stayed intact for 20 days. The outstanding XRD results indicated that the intensity of perovskite's Miler indices increased significantly after 24 h, and the MAI's Miler indices decreased, which means that the amount of MAI was consumed to renew the perovskite crystal structure. In particular, the results suggested that the charging of MAI using the excess molar ratio of MAI reconstructs the perovskite material and stabilizes the crystal structure over time. Therefore, it is crucial that the main preparation procedure of perovskite material is optimized to 1 unit of Pb and 25 units of MAI in a two-step procedure in the literature.

Perspectives for the conversion of perovskite indoor photovoltaics into IoT reality

As a competitive candidate for powering low-power terminals in Internet of Things (IoT) systems, indoor photovoltaic (IPV) technology has attracted much attention due to its effective power output under indoor light illumination. One such emerging photovoltaic technology, perovskite cell, has become a hot topic in the field of IPVs due to its outstanding theoretical performance limits and low manufacturing costs. However, several elusive issues remain limiting their applications. In this review, the challenges for perovskite IPVs are discussed in view of the bandgap tailoring to match indoor light spectra and the defect trapping regulation throughout the devices. Then, we summarize up-to-date perovskite cells, highlighting advanced strategies such as bandgap engineering, film engineering and interface engineering to enhance indoor performance. The investigation of indoor applications of large and flexible perovskite cells and integrated devices powered by perovskite cells is exhibited. Finally, the perspectives for the perovskite IPV field are provided to help facilitate the further improvement of indoor performance.

In situ crystal reconstruction strategy-based highly efficient air-processed inorganic CsPbI2Br perovskite photovoltaics for indoor, outdoor, and switching applications

All-inorganic CsPbI₂Br (CPIB) perovskite has gained strong attention due to their favorable optoelectronic properties for photovoltaics. However, solution-processed CPIB films suffer from poor morphology due to the rapid crystallization process, which must be resolved for desirable photovoltaic performance. We introduced phenethylammonium iodide (PEAI) as an additive into a perovskite precursor that effectively controls the crystallization kinetics to construct the preferred quality α-CPIB film under ambient conditions. Various photophysical and structural characterization studies were performed to investigate the microstructural, morphological, and optoelectronic properties of the CPIB and PEAI-assisted perovskite films. We found that PEAI plays a vital role in decreasing pinholes, ensuring precise crystal growth, enhancing the crystallinity, improving the uniformity, and tailoring the film morphology by retarding the crystallization process, resulting in an improved device performance. The device based on the optimized PEAI additive (0.8 mg) achieved a respectably high power conversion efficiency (PCE) of 17.40% compared to the CPIB perovskite solar cell (PSC; 15.75%). Moreover, the CPIB + 0.8 mg PEAI PSC retained ∼87.25% of its original PCE, whereas the CPIB device retained ∼66.90% of the initial PCE after aging in a dry box at constant heating (85 °C) over 720 h, which revealed high thermal stability. Furthermore, the indoor photovoltaic performance under light-emitting diode (LED) lighting conditions (3200 K, 1000 lux) was investigated, and the CPIB + 0.8 mg PEAI PSC showed a promising PCE of 26.73% compared to the CPIB device (19.68%). In addition, we developed a switching function by employing the optimized PSC under LED lighting conditions, demonstrating the practical application of constructed indoor PSCs.

Tailoring Defects Regulation in Air-Fabricated CsPbI3 for Efficient Inverted All-Inorganic Perovskite Solar Cells with Voc of 1.225 V

Air fabrication of CsPbI₃ perovskite photovoltaics has been attractive and fast-moving owing to its compatibility to low-cost and up-scalable fabrication. However, due to the inevitable erosions, undesirable traps are formed in air-fabricated CsPbI₃ crystals and seriously hinder photovoltaic performance with poor reproduction. Here, 3, 5-difluorobenzoic acid hydrazide (FBJ) is incorporated as trap regulation against external erosions in air-fabricated CsPbI₃. Theoretical simulations reveal that FBJ molecules feature stronger absorbance on CsPbI₃ than water, which can regulate trap formations for water erosions. In addition, FBJ with solid bonding interaction to CsPbI₃ can enlarge formation energy of various defects during crystallization and further suppress traps. Moreover, profiling to reductive hydrazine groups, FBJ inhibits traps for oxidation erosions. Consequently, a champion efficiency of 19.27% with an impressive V_oc of 1.225 V is realized with the inverted CsPbI₃ devices. Moreover, the optimized devices present superior stability and contain 97.4% after operating at 60 °C for 600 h.

Insights Into to the KX (X = Cl, Br, I) Adsorption-Assisted Stabilization of CsPbI2 Br Surface

Despite the excellent optoelectronic properties, organic-inorganic hybrid perovskite solar cells (PSCs) still present significant challenges in terms of ambient stability. CsPbI₂ Br, a member of all-inorganic perovskites, may respond to this challenge because of its inherent high stability against light, moisture, and heat, and therefore has gained tremendous attraction recently. However, the practical application of CsPbI₂ Br is still impeded by the notorious phenomenon of photoinduced halide segregation. Herein, by applying first-principles calculations, the stability, electronic structure, defect properties, and ion-diffusion properties of the stoichiometric CsPbI₂ Br (110) surface and that with the adsorption of KX (X = Cl, Br, I) are systematically investigated. It is found that the adsorbed KX can serve as an external substitute of the halogen vacancies on the surface, therefore inhibiting halogen segregation and improving the stability of the CsPbI₂ Br surface. The KX can also eliminate deep-level defect states caused by antisites, thereby contributing to the promoted optoelectronic properties of CsPbI₂ Br. The mechanistic understanding of surface passivation in this work can lay the foundation for the future design of CsPbI₂ Br PSCs with optimized optoelectronic performance.

Reducing Defects of All-Inorganic γ-CsPbI2Br Thin Films by Ethylammonium Bromide Additives for Efficient Perovskite Solar Cells

Obtaining good-quality perovskite thin films is a fundamental facet that contributes to efficient inorganic perovskite solar cells. Herein, we successfully deposited ethylammonium bromide (EABr) additive-assisted high quality γ-CsPbI₂Br perovskite films under ambient conditions. Detailed morphological, structural, optical, charge transport, photovoltaic performance, and stability properties have been studied. It is observed that the EABr additive helps to retard the crystal growth of perovskite films to produce a highly crystalline perovskite film with microsized grains (>1 μm) and with reduced grain boundaries. The fabricated devices based on an optimum amount of EABr (4 mg mL^-1) exhibited the highest 14.47 % power conversion efficiency. Moreover, the EABr-4 mg mL^-1-assisted γ-CsPbI₂Br-based devices achieved a high thermal long-term stability and maintained ∼75% of their initial efficiency over 180 h at 85 °C thermal stress under ambient conditions (relative humidity: ∼35%) without encapsulation. This additive-assisted method suggests a new pathway to achieve high-quality perovskite films with a stabilized photoactive black phase and efficient devices.