Improving the Power Conversion Efficiency and Stability of Planar Perovskite Solar Cells via Small Molecule Doping

Pinhole-free small molecule (SM)-doped perovskite films have been synthesized to improve the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). Thin films of pristine perovskite and doped with SMs such as [6,6]-phenyl C-60 butyric acid methyl ester (PCBM) and N,N-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxylic diimide (EP-PDI) were prepared on glass/indium-doped tin oxide (ITO)/poly(3,4-ethylenedioxythio-phene):polystyrene sulfonate (PEDOT:PSS) substrate for perovskite solar cells with planar geometry. Both perovskite and doped perovskite:SM films were investigated for their optical, morphological, and photovoltaic properties. Doping with trace amount (0.1wt.%) of PCBM improved the morphology of the perovskite films, with increased grain size and crystallinity, resulting in an increase of the PCE of the PSC by 35%. The improved morphology of the perovskite:SM system also played an important role in improving the device stability. Furthermore, temperature-dependent electron mobility measurements revealed a significant decrease in charge carrier trapping or defect states in the perovskite:SM system. Evidently, the lower activation energy (E-a) in the perovskite:SM system explains the higher electron mobility in comparison with the reference perovskite system.