Efficient and thermally stable CH3NH3PbI3 based perovskite solar cells with double electron and hole extraction layers

In this paper, we report an efficient and thermally stable CH3NH3PbI3 based perovskite solar cell with a double decked hole (H) and electron (E) extraction layers (EL) in an inverted (p-i-n) architecture. The double HEL film is fabricated by thermal evaporation of MoO3 and spin-coating of poly(3,4-ethylene dioxy-thiophene)-poly(styrene sulfonate) (PEDOT:PSS). The double EEL is formed by spin-coating of phenyl-C61-butyric acid methyl ester (PC60BM) and bathocuproine (BCP). We investigate the effect of each additional second HEL and/or EEL interlayer on the photovoltaic parameters of the perovskite solar cells. We observed that the underneath MoO3 layer provides an improved morphology for perovskite film and reduces the shunt path. However, the BCP buffer interlayer passivates the defects at the perovskite-EEL interface and helps to planarize the thin-films for better contact with Ag. Thus, double EEL and HEL facilitate better charge collection at the interfaces and shows improved power conversion efficiency (PCE) of similar to 15%. Besides the improved PCE, double EEL and HEL based structures also provide an approach to have better reproducibility and high thermal stability of perovskite solar cells. We also address the issue of area dependent efficiency and explore the reasons behind the increased efficiency of smaller area devices. We believe reproducibility, stability and area dependence are the most important aspects for current perovskite PV research and thus this study will provide an important insight for further development. Moreover, this approach can be useful for other optoelectronic devices too, based on wider bandgap and multi-cation mixed halide-based perovskite semiconductors.