Hole Transport Bilayer for Highly Efficient and Stable Inverted Perovskite Solar Cells

We demonstrate that using a hole transport bilayer composed of poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and CuI leads to highly efficient and stable inverted, that is, p–i–n, perovskite solar cells (PSCs). The bilayer-based devices had an average power conversion efficiency (PCE) of 19.4% and a maximum PCE of 20.34%. In comparison, devices with a single PTAA interlayer showed an average PCE of 17.7%. Perovskite films fabricated on PTAA/CuI bilayers showed improved crystallinity and larger grain sizes. Data from ultraviolet photoelectron spectroscopy and Mott–Schottky analysis of impedance suggest an increased built-in potential within the device with enhanced upward band bending at the CuI interface. The bilayered HTL devices have minimum current–voltage hysteresis and stable current output at the maximum power point. These devices were stable for more than 4500 h under ambient light in an inert atmosphere.