Inorganic Charge Transport Layers for High-Performance p-i-n Perovskite Solar Cells

Perovskite solar cells (PSCs) with an inverted (p-i-n) configuration have attracted growing interest due to their reduced hysteresis, simplified low-temperature processing, and excellent compatibility with monolithic tandem architectures. Although record power conversion efficiencies (PCEs) above 27% have been achieved, these high-performance p-i-n PSCs still predominantly rely on organic charge transport layers (CTLs), which suffer from limited intrinsic stability and elevated production costs. Inorganic CTLs, by contrast, offer superior thermal and chemical stability, as well as lower material costs, positioning them as promising alternatives for scalable and durable PSC technologies. However, the efficiency of devices incorporating inorganic CTLs remains inferior to their organic counterparts, largely due to interfacial challenges and suboptimal charge extraction. This review systematically summarizes recent advances in inorganic CTLs, encompassing both electron transport layers (ETLs) and hole transport layers (HTLs), with an emphasis on their structure-property-performance relationships. We critically assess representative materials, deposition methods, and interfacial engineering strategies. Finally, we discuss current limitations and propose future research directions toward enhancing efficiency, stability, and manufacturability in p-i-n PSCs and tandem photovoltaic systems.