Light Soaking Effect on Band Bending of the MAPbI3-Based Perovskite Solar Cell with Nano-ZnO as Electron-Transport Material

Sheng-Wei Hsiao^1,2*, Pin-Jiun Wu², Yu-Ting Chen³, Mei-Hsin Chen⁴, Wu-Ching Chou¹

¹Institute and Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
²Industrial Application Group, National Synchrotron Radiation Research Center, Hsinchu, Taiwan
³Department of Opto-Electronic Engineering, National Dong Hwa University, Hualien, Taiwan
⁴Department of Electro-Optical Engineering, National Taipei University of Technology, Taipei, Taiwan

* Presenter:Sheng-Wei Hsiao, email:jasongodya@gmail.com

Perovskite-based solar cells (PSCs) have attracted much attention over the past decade in academy and industry because of its high power conversion efficiency (PCE%) and low-cost fabrication. Electron transporting materials (ETMs) play a crucial role in PSCs performance by compensating the difference of diffusion lengths between holes and electrons, and serve as a block layer to prevent holes transported from the perovskite active layer. As compared to TiO2, ZnO has advantages to act as ETM for PSCs due to its higher electron mobility and material abundance. In this work, CH3NH3PbI3 (MAPbl3) active layers (~400 nm) were spin-coated on two kinds of ZnO ETMs, ZnO thin film (ZnOfilm) and ZnO nanoparticles (ZnOnano), with surface roughness of 24.6nm and 12.9nm, respectively. Our preliminary results reveal that the roughness of MAPbI3 is obviously influenced by roughness of its bottom layer (ZnOfilm/MAPbI3 and ZnOnano/MAPbI3 with surface roughness of 20.1 nm and 8.4 nm, respectively), which further affects the PSCs performance (with PCE% as 7.2% to 15.4%, respectively). To understand the mechanism behind PCE% enhancement and the corresponding variations of electronic structure under light exposure, we utilized hard X-ray photoelectron spectroscopy (HAXPES) cooperated with xenon lamp as a solar simulator to investigate the real band bending behaviors on the electronic structure of MAPbI3 under light soaking. For ZnOnano/MAPbI3, a downward band bending can be observed under light soaking, which is attributed to a better crystallinity and a higher concentration ratio of stoichiometric MAPbI3/PbI2 for MAPbI3 on the ZnOnano ETM.

Keywords: ZnO, MAPbI3, solar cell