Exploring the interfacial effects at the ETL/perovskite boundary in the semitransparent perovskite solar cells

The recent focus has been made on the perovskite solar cells (PSCs) with an inverted configuration, where substantial improvements have been already achieved. However, the p-i-n structure needs a buffer layer for most of the configurations to modify the work-function of a deposited electrode. Additionally and very importantly, such a layer can also serve as a protective film that improves a stability of solar cells. Here, we study the semitransparent inverted PSCs, which have been prepared with the SnO2 buffer layer deposited by a spin-coating method. The main goal was to understand the dominant loss mechanisms in the operation of PSCs. Four photovoltaic parameters (an open-circuit voltage, a short-circuit current, a fill factor and a power conversion efficiency) were measured for a wide range of the light intensity. Their analysis allowed us to identify the transportation and recombination effects using an electrical modeling based on the drift-diffusion model. In addition, it has been concluded that the solution processed PCBM layer might not fully cover the perovskite film. As a consequence, the band-bending effect can occur at the PCBM/perovskite interface, where PCBM plays a role of the Electron Transport Layer (ETL). Therefore, we theoretically investigated the influence of this interface phenomenon on four photovoltaic parameters and the ideality factor simulated as a function of the ETL interface defect density. The increasing of the ideality factor to a high value (above 4) observed for the band-bending level around 300 eV indicates inhomogeneity of the interface. The results of this study should help to better understand the dominant electrical losses in the semitransparent inverted PSCs with a buffer layer which should further help to improve the performance of such devices.