In this work, a simple and efficient method for the extraction of all the parameters of a solar cell from a single current-voltage (I-V) curve under the constant illumination level is proposed. With the help of the Lambert W function, the explicit analytic expression for I is obtained. By reducing the number of the parameters, the expression for I only depends on the ideality factor n, the series resistance R_s, and the shunt resistance R_sh. This analytic expression is directly used to fit the experimental data and extract the device parameters. This simple solar cell parameter extraction method can be directly applied for all kinds of solar cells whose I-V characteristics follow the single-diode model. The parameters of various solar devices including silicon solar cells, silicon solar modules, dye-sensitized solar cells, and organic solar cells with standalone, tandem, and multi-junction structures have been successfully extracted by using our proposed method.

Recent research shows that the interface state in perovskite solar cells is the main factor which affects the stability and performance of the device, and interface engineering including strain engineering is an effective method to solve this issue. In this work, a CsBr buffer layer is inserted between NiO_x hole transport layer and perovskite layer to relieve the lattice mismatch induced interface stress and induce more ordered crystal growth. The experimental and theoretical results show that the addition of the CsBr buffer layer optimizes the interface between the perovskite absorber layer and the NiO_x hole transport layer, reduces interface defects and traps, and enhances the hole extraction/transfer. The experimental results show that the power conversion efficiency of optimal device reaches up to 19.7% which is significantly higher than the efficiency of the device without the CsBr buffer layer. Meanwhile, the device stability is also improved. This work provides a deep understanding of the NiO_x/perovskite interface and provides a new strategy for interface optimization.

Flexible perovskite solar cells (FPSCs) have attracted enormous interest in wearable and portable electronics due to their high power-per-weight and low cost. Flexible and efficient perovskite solar cells require the development of flexible electrodes compatible with the optoelectronic properties of perovskite. In this review, the recent progress of flexible electrodes used in FPSCs is comprehensively reviewed. The major features of flexible transparent electrodes, including transparent conductive oxides, conductive polymer, carbon nanomaterials and nanostructured metallic materials are systematically compared. And the corresponding modification strategies and device performance are summarized. Moreover, flexible opaque electrodes including metal films, opaque carbon materials and metal foils are critically assessed. Finally, the development directions and difficulties of flexible electrodes are given.

Perovskite solar cells (PSCs) have attracted much attention due to their impressive photovoltaic performance and low fabrication cost. The perovskite layer plays a critical role in light-to-electricity conversion. Here we study the effects of alkali metal ion dopants on the growth, structure and properties of perovskite films and the photovoltaic performance of PSCs. At a low doping level, the alkali metal ions can significantly affect the formation and properties of the perovskite films. They can enhance the short-circuit current density (J_sc) and power conversion efficiency (PCE) significantly. The J_sc increases significantly from 19.2 mA cm⁻² to 21.0 mA cm⁻² and 20.3 mA cm⁻² for the PSCs with a methylammonium lead triode layer doped with 0.5 mol% K⁺ and 0.25 mol% Na⁺, respectively, and the fill factor (FF) increases from 0.74 to 0.79 for the devices with both doping ions. Correspondingly, the PCE increases from 13.7% to 15.3% and 14.6% for the PSCs, respectively. The efficiency improvement by K⁺ or Na⁺ doping is attributed to their effect in increasing the crystallinity and crystallite size of the perovskite films.