A fluorene-carbazole conjugated polymer hole conductor for efficient and stable perovskite solar cells

Semiconducting lead halide perovskites are currently attracting increasing attention, showing great potential for next-generation photovoltaic devices. To date, the molecular hole conductor 2,2 ',7,7 '-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9 '-spirobifluorene (spiro-OMeTAD) has been dominantly used as the hole transport material (HTM) in these solar cell devices, but is notorious for causing device instability. Here, we for the first time report a promising and easily accessible fluorene-carbazole conjugated polymer hole conductor, namely PF8Cz, as an alternative HTM for efficient and stable perovskite solar cells (PSCs). The PSCs based on PF8Cz have an excellent capability to achieve efficient charge extraction at perovskite/polymer interfaces due to their appreciable energy level alignment, as well as high hole mobility, and avoid instability caused by doping and oxidation processes in spiro-OMeTAD based PSCs. Meanwhile, PF8Cz can be solution processed over a large area and exhibits a more uniform and reproducible film morphology. Through detailed optimization, we have demonstrated PF8Cz based PSCs with a remarkable efficiency of 23.28% and significantly improved ambient, thermal and operational stability. In comparison with the state-of-the-art polymeric hole conductor poly[bis(4-phenyl)(2,4,6-trimethyl-phenyl)amine] (PTAA) (20.38%) and spiro-OMeTAD (23.55%), we believe that PF8Cz can well balance the interplay of cost, processing and performance, and more importantly, catalyze further development of high-performance organic HTMs and help realize the promising potential of PSCs. Semiconducting lead halide perovskites are currently attracting increasing attention, showing great potential for next-generation photovoltaic devices.