In recent years, Cu–Ag–Bi–I quaternary lead-free perovskites have emerged as promising candidates for optoelectronic applications, offering an environmental alternative to traditional lead-based perovskites. This review presents a comprehensive analysis of the current advancements in the synthesis, structural characterization, and photoelectric properties of Cu–Ag–Bi–I compounds, with a focus on their photoelectric applications, including solar cells, indoor photovoltaics, and photodetectors. The unique combination of metal cations in Cu–Ag–Bi–I materials leads to tunable bandgaps, high absorption coefficients, and favorable charge transport properties, positioning them as versatile materials for various optoelectronic applications. Despite their potential, challenges remain in optimizing their performance and stability. We discuss current strategies, such as additive engineering and doping, to enhance material properties and suggest future directions for the development of these materials. Ultimately, Cu–Ag–Bi–I lead-free perovskites has significant potential for commercialization as a burgeoning green and efficient photoelectric materials.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), an ordinary hole transport layer (HTL), has inherent shortcomings that restrict its use in Sn–Pb perovskite solar cells (PSCs). In this study, PEDOT:PSS was mixed with ethanol using a simple solution method, resulting in enhanced conductivity and an optimized work function. By varying the concentration of ethanol doping, the insulated PSS shell surrounding the PEDOT:PSS was stripped, and the conductivity of PEDOT:PSS was increased from 4.50 × 10⁻⁴ S cm⁻¹ to 7.00 × 10⁻⁴ S cm⁻¹. The work function was lowered by 0.23 eV to −5.30 eV, bringing it closer to the energy level of Sn–Pb perovskite. Ethanol-doped PEDOT:PSS was utilized as the HTL in Sn–Pb PSCs based on FA_0.5MA_0.5Sn_0.5Pb_0.5I₃, resulting in 18.10% photoelectric conversion efficiency with negligible hysteresis, and more than 40% performance improvement compared to the undoped devices. Furthermore, the treatment of ethanol could enhance the stability of the devices. The doped device was placed in a glove box for one month, and its efficiency remained above 90% of the maximum value. Thus, ethanol doping in PEDOT:PSS should provide a promising strategy for developing HTLs in efficient Sn–Pb PSCs.

Bismuth-based perovskite derivatives, (CH₃NH₃)₃Bi₂I₉ (MBI), are promising non-toxic light-absorbing materials widely used in various photoelectric devices because of their excellent stability. However, MBI-based perovskite solar cells (PSCs) are limited by poor film quality, and the performance of such a device is far behind that of lead-based PSCs. In this work, the crystal structure and morphological properties of MBI films were compared across different preparation methods. The two-step vapor-assisted method can prepare continuous dense MBI films because MBI crystal nucleation is induced by the BiI₃ seed layer. The MBI film grown by this method is better for the production of excellent PSCs compared to the film prepared by the solution method. The best photovoltaic device based on the MBI film could obtain a power conversion efficiency of 1.13%. An MBI device is stored in the glove box for 60 days, and the device’s performance is maintained at 99%. These results indicate that the vapor-assisted deposition of MBI films can be an effective method to improve the performance of bismuth-based planar PSCs.

Lead halide perovskite solar cells (PSCs) have shown tremendous progress in the last few years. However, highly toxic Pb and its instability have restricted their further development. On the other hand, antimony-based perovskites such as cesium antimony iodide (Cs₃Sb₂I₉) have shown high stability but low power conversion efficiency (PCE) due to the limited transfer of photocarriers and the poor quality of films. Here, we present a novel method to improve the performance of Cs₃Sb₂I₉ PSCs through a FACl-modified buried interface. FACl acts as a bi-functional additive, and FA incorporation enhances the crystallinity and light absorption of films. Furthermore, treatment with FACl optimizes the level position of Cs₃Sb₂I₉. In addition, transient photovoltage and transient photocurrent were employed to confirm the reduction of charge recombination and superior carrier transportation. By using a planar device structure, we found the PCE of a FACl–Cs₃Sb₂I₉-based device to be 1.66%. The device, stored for 2 months under N₂ conditions, showed a negligible loss in PCE. Overall, this study provides a new strategy to further enhance the performance of Sb-based PSCs.