Improved hole interfacial layer for planar perovskite solar cells with efficiency exceeding 15%.

Planar structure has been proven to be efficient and convenient in fabricating low-temperature and solution-processing perovkite solar cells (PSCs). Interface control and crystal film growth of organometal halide films are regarded as the most important factors to obtain high-performance PSCs. Herein, we report a solution-processed PEDOT: PSS-GeO2 composite films by simply incorporating the GeO2 aqueous solution into the PEDOT: PSS aqueous dispersion as a hole transport layer in planar PSCs. Besides the merits of high conductivity, ambient stability and interface modification of PEDOT: PSS-GeO2 composite films, the formed island-like GeO2 particles are assumed to act as growing sites of crystal nucleus of perovskite films during annealing. By the seed-mediation of GeO2 particles, a superior CH3NH3PbI(3-x)Cl(x) crystalline film with large-scale domains and good film uniformity was obtained. The resulting PSC device with PEDOT: PSS-GeO2 composite film as HTL shows a best performance with 15.15% PCE and a fill factor (FF) of 74%. There is a remarkable improvement (∼37%) in PCE, from 9.87% to 13.54% (in average for over 120 devices), compared with the reference pristine PEDOT: PSS based device.