Hole transport layer-free carbon-based perovskite solar cells with high-efficiency up to 17.49% in air: From-bottom-to-top perovskite interface modification

Low-cost hole transport layer (HTL)-free carbon-based perovskite solar cells (C-PSCs) have drawn considerable interest owing to their simple manufacturing process and excellent stability. However, the insufficient interfacial charge transport severely limits the efficiency of HTL-free C-PSCs. In this paper, a from-bottom-to-top dual interfacial modification (DIM) strategy is developed by adopting FAX (X = I, Br) to modify perovskite interfaces and thus to intensify charge transport at SnO2/perovskite and perovskite/carbon interfaces. The underlying FABr is employed to regulate the composition at the bottom region of the perovskite films by the reaction of FABr and its upper PbI2 & MAI, yielding a favorable band alignment at SnO2/perovskite. The FAI is used to fill the gaps at upper perovskite/carbon interface to boost the two-layer contact via the penetration of FAI across carbon electrode, and subsequent reaction with the residual PbI2. Such dual-modified perovskite films exhibit improved crystallinity and thus reduced trap state density. On account of the above merits, the dual-modified HTL-free C-PSCs with an architecture of ITO/SnO2/perovskite/carbon present a power conversion efficiency up to 17.49 % in air. Moreover, the C-PSCs exhibit superior ambient stability maintaining 96 % of its initial performance under storage in ambient air condition up to 60 days due to carbon electrode being filled by the penetrated FAI against the moisture erosion.