Chemical doping engineering by utilizing trilacunary Keggin polyoxometalates as a dopant for high performance perovskite solar cells

Chemical doping engineering is an effective strategy to modify the hole transport layer (HTL) and achieve high-efficiency perovskite solar cells (PSCs). In this work, we synthesize an infrequent trilacunary Keggin type polyoxometalate Na10[Zn2(H2O)6(WO2)2(BiW9O33)2] (BiW9-Zn) and apply it as an additive to enhance the hole mobility and electrical conductivity of Spiro-OMeTAD based HTLs. Thanks to the strong electron-accepting properties of polyoxometalate molecules, the as-synthesized BiW9-Zn can directly oxidize Spiro-OMeTAD under an inert atmosphere and avoid the tedious long-term oxidation process. Therefore, the power conversion efficiency (PCE) of optimal PSCs with BiW9-Zn doping is enhanced from 17.58% (without doping) to 19.56% with a significantly improved fill factor and open-circuit voltage. In addition, the assembly repeatability and long-term stability of PSCs are also improved. This work demonstrates the potential of using polyoxometalates (POMs) as low-cost, efficient and highly flexible chemical dopants for HTLs, and more importantly paves a new route to enhance the performance of PSCs.