Perovskite-perovskite junctions for optoelectronics: Fundamentals, processing, and applications

Electrical doping of materials and the assembly of these doped materials have forged most optoelectronic technologies. However, it has only recently taken the spotlight for perovskite optoelectronics owing to challenges in reliable doping and perovskite-perovskite junction (PPJ) processing. Of those, the doping issues have been critically examined, but no efforts have been made to dissect the processing of the PPJ. This review aims to fill such a research gap by providing in-depth insights into the synthetic routes developed for PPJ fabrication, which will inject momentum for perovskite solar cells and beyond. It is started by the fundamentals of the PPJ. Then, limitations of the PPJ fabrication suffered by traditional processes are highlighted, and the process innovations that circumvent these limitations are comprehensively analyzed. This is followed by a review on the implementation of PPJs for various optoelectronics. Finally, it comes to the summary and the outlook of future directions.