Improved photostability of inverted-structure perovskite solar cells with high power conversion efficiency by inserting CuI between PEDOT and MAPbI 3 layers

Inverted-structure perovskite devices with PEDOT and PEDOT/CuI as hole transport layers (HTLs) were prepared on Glass/ITO substrates. Surface morphology observation of the CuI revealed that the CuI grew on PEDOT in island mode. A concentration of 20 mg/ml was necessary for continuous CuI formation on the PEDOT. Optimization of the annealing time and the concentration of CuI precursor solution led to a PCE of 16.5% for a device with PEDOT/CuI as HTL, which was slightly higher than that (15%) with PEDOT as HTL. The slight enhancement of PCE was due to the faster hole transport efficiency and improved light-harvesting in the visible light region. Additionally, the photostability of the devices was greatly enhanced by the insertion of the CuI layer. Analysis indicated that the insertion of the CuI decreased the transmittance of light with wavelengths within 320–410 nm, which was the main reason for the enhanced photostability.