Homojunction perovskite solar cells: opportunities and challenges

Organometallic halide perovskites have rapidly become promising materials as a result of their outstanding properties in high-efficiency and low-cost next-generation solar cells. Perovskite materials can be adjusted to be p- or n-type by defect engineering through, for example, the self-doping method by controlling the precursor compositions and process conditions. Recently, a p-type perovskite/n-type perovskite homojunction has been proposed and constructed, which provides a possibility for the design of a novel type of perovskite solar cell (PSC). Following a brief overview of the physical fundamentals of perovskite homojunctions, a detailed discussion of the promising progress of recently reported homojunction PSCs is presented here, including theoretical simulations, extrinsic and interfacial doping and graded structures. Furthermore, the opportunities regarding higher doping concentrations, simpler device architectures, ion migration inhibition and device stability are discussed. Finally, an outlook that offers insights into the future development of highly efficient and stable homojunction PSCs is provided.