Interface engineering of TiO2/perovskite interface via fullerene derivatives for high performance planar perovskite solar cells

The performance of planar perovskite solar cells (PSCs) is very sensitive to the interfaces properties, especially the electron transport layer (ETL)/perovskite interface in the n-i-p structure, which could significantly influence the perovskite film morphology, crystallinity and the charge extraction and collection efficiency. Therefore, interface engineering is crucial for achieving high performance planar PSCs. Here, we reported a simple and effective interface engineering method which employed phenyl-C-61-butyric acid methyl ester (PC61BM) thin film or fullerene (C-60) self-assembled monolayer (SAM) or their combination to modify the titanium dioxide (TiO2)/perovskite interface to obtain high performance PSCs. A comparative study between the effects of different fullerene derivative modifications was taken and indicated that adding proper C-60-SAM into the PC61BM solution could improve the interface contact, increase the charge extraction and collection efficiency more obviously compared to the pristine PC61BM treatment. By combining the modified two-step spin coating method, the best performance device based on C-60-SAM modified TiO2 achieved a power conversion efficiency (PCE) of 17.8%, much higher than the control device without the interface treatment (12.9%) and also higher than the PC61BM modified device (16.1%) based on MA(1-y)FA(y)PbI(3-x)Cl(x) perovskite. As a consequence, such interface engineering via C-60-SAM or PC61BM + C-60-SAM combination modification is a promising method for achieving highly efficient PSCs.