Carbon-based all-inorganic perovskite solar cells: Progress, challenges and strategies toward 20% efficiency

Organic-inorganic hybrid perovskite solar cells (PSCs) are promising next-generation photovoltaic technology. However, their long-term operation is limited due to thermodynamic instability of hybrid perovskites (loss of organics) and severe migration of constituents (ions and dopants). PSCs have to be free of volatile organics and mobile dopants to become commercially relevant. PSCs based on cesium lead halide inorganic perovskites (CsPbI3_xBrx, x = 0 similar to 3) and a carbon electrode, abbreviated here as C-IPSCs, fulfill these requirements: CsPbI3_xBrx is stable against decomposition to binary halides and the carbon electrode is inherently moisture-resistive and dopant-free. Since the first report of C-IPSCs in 2016, their power conversion efficiencies (PCEs) have doubled, recently reaching 14.84% with an astonishing stability of over 2000 h at 80 degrees C and 80% relative humidity (RH). Here we review recent progress of C-IPSCs and analyze the remaining critical issues in the field. We then offer our perspective to address these challenges through morphology, interface, spectral and material engineering. Finally, we argue that C-IPSCs have potential to overcome the 20% efficiency milestone, making them - in combination with their already impressive stability - the most promising PSC architecture for commercialization.