Device physics of homojunction perovskite solar cells: a design omitting all the charge transport layers with efficiency exceeding 26.3%

Abstract

Abstract Perovskite solar cells (PSCs) omitting all the charge transport layers with p–n homojunction structure are considered a promising alternative for commercialization owing to their low fabrication cost and simplified structure. Deep understanding of the device physics of these all-free p–n homojunction structured PSCs is of paramount importance. Here, a thorough investigation of all-free perovskite–perovskite p–n homojunction structured PSCs is performed by using a photoelectrical coupling model. Four different configurations including a standard n–i–p cell, electron transport layer-free cell, hole transport layer-free cell, and all-free cell are compared to identify the limiting performance factors, and the results indicate that no extra built-in electric field in the perovskite layer and severe surface recombination occurring at the perovskite interface are the two main factors limiting the power conversion efficiency (PCE) of all-free p–n homojunction structured PSCs. Based on doping engineering, a highly efficient all-free p–n homojunction structure is designed, which consists of an asymmetric p–n junction with both a front surface field layer and a back surface field layer. The effects of optical loss, thickness of the emitter, doping concentration for both the emitter and base, and diffusion length on the performance of p–n homojunction structured PSCs are optimized. After optimization, the PCE of the all-free p–n homojunction structured PSCs reaches 26.33%, which is slightly higher than that of a standard n–i–p heterojunction cell (26.22%). This work demonstrates that all-free p–n homojunction structured PSCs are a promising alternative to standard n–i–p heterojunction structured PSCs for realizing high efficiency, which may pave the way toward commercialization of PSCs in the future.