Introducing Cu2O Thin Films as a Hole-Transport Layer in Efficient Planar Perovskite Solar Cell Structures

Abstract

Abstract In this work, we introduce Cu2O thin films as a hole-transport layer in planar perovskite solar cells. Here, a Cu2O layer was formed through successive ionic layer adsorption and reaction (SILAR) method. With methylammonium lead triiodide (MAPbI3) we form a direct structure (p–i–n), where the perovskite layer is sandwiched between a layer of p-type Cu2O and another layer of n-type PCBM (phenyl-C61-butyric acid methyl ester), which acted as hole- and electron-transport materials, respectively. We locate band edges of the materials with respect to their Fermi energy by recording scanning tunneling spectroscopy that has correspondence to their density of states (DOS). We observe that the energy levels of the materials form type II band alignments at each of the two interfaces (p–i and i–n) for charge separation and uninterrupted carrier transport upon illumination. Such a band alignment enabled charge transfer from MAPbI3 as evidenced from quenching of its photoluminescence emission when the perovskite was in contact with either the hole- or the electron-transport layer. With the direct p–i–n structure having appropriate energy levels for carrier separation, the planar perovskite solar cell (Cu2O/MAPbI3/PCBM) yielded an energy conversion efficiency (η) of 8.23% under 1 sun illumination.