Solution-Processed Metal Oxide Nanocrystals as Carrier Transport Layers in Organic and Perovskite Solar Cells

There has been rapid progress in solution-processed organic solar cells (OSCs) and perovskite solar cells (PVSCs) toward low-cost and high-throughput photovoltaic technology. Carrier (electron and hole) transport layers (CTLs) play a critical role in boosting their efficiency and long-time stability. Solution-processed metal oxide nanocrystals (SMONCs) as a promising CTL candidate, featuring robust process conditions, low-cost, tunable optoelectronic properties, and intrinsic stability, offer unique advantages for realizing cost-effective, high-performance, large-area, and mechanically flexible photovoltaic devices. In this review, the recent development of SMONC-based CTLs in OSCs and PVSCs is summarized. This paper starts with the discussion of synthesis approaches of SMONCs. Then, a broad range of SMONC-based CTLs, including hole transport layers and electron transport layers, are reviewed, in which an emphasis is placed on the improvement of the efficiency and device stability. Finally, for the better understanding of the challenges and opportunities on SMONC-based CTLs, several strategies and perspectives are outlined.