CsPbI2Br Perovskite Solar Cells Based on Carbon Black-Containing Counter Electrodes.

CsPbI2Br perovskite solar cells (PSCs) based on carbon electrodes (CEs) are considered to be low-cost and thermally stable devices. Nevertheless, the insufficient contact and energy level mismatch between the CsPbI2Br layer and CE hinder the further enhancement of the cell efficiency. Herein, a carbon black (CB) interlayer was introduced between the perovskite layer and CE. The hole extraction was facilitated due to the larger contact area and suitable energy band alignment in the CsPbI2Br/CB interface. Further investigation indicated the diffusion of CB nanoparticles from the CE or CB layer to the CsPbI2Br film after a certain period of time. We disclosed the formation of a CB-CsPbI2Br bulk heterojunction structure due to the carbon diffusion, which resulted in an efficiency enhancement. As a result, a record efficiency of 13.13% is achieved for carbon-based inorganic PSCs. This work also reveals that the diffusion of CB nanoparticles in CB-containing PSCs is universal and inevitable, although this kind of diffusion results in the enhancement of cell efficiency.