Advanced carbon-based rear electrodes for low-cost and efficient perovskite solar cells

Perovskite solar cells (PSCs) as new-generation photovoltaic cells have received remarkable interest due to the facile fabrication procedures and superb power conversion efficiencies (PCEs). Nevertheless, the widely used noble metal-based rear electrodes such as Ag and Au in PSCs suffer from the relatively high material costs and instability induced by the halide anion degradation reaction, strongly hindering the practical applications of PSCs. Consequently, carbon-based materials are considered as some of the most encouraging candidates to substitute noble metals as rear electrodes due to the cost effectiveness, superior physical/chemical stability, superb structural flexibility and diverse/easily tuned properties to realize low-cost and highly robust PSCs. However, the carbon electrode-based PSCs still suffer from the much inferior PCEs to those of the noble metal-based counterparts due to the insufficient carrier transfer capability and inferior interface contact. In this paper, the recent advancements in the design and fabrication of advanced carbon-based rear electrodes for low-cost and efficient PSCs are reviewed by highlighting the unique merits of carbon-based rear electrodes over metal/metal oxide-based counterparts. Several distinct strategies are also proposed to improve the PCEs and durability of carbon electrode-based PSCs. Lastly, the current challenges and future directions of carbon-based rear electrode-based PSCs are also highlighted and discussed, intending to present vital insights for the future development of low-cost carbon-based PSCs towards the scalable production and widespread applications of this technology.