Direct evidence of chemical interaction and origin of electron accumulation at a “buried” methylammonium lead triiodide (CH3NH3PbI3, hereafter “MAPI”)/TiO2 interface is presented in this study for the first time. Despite the high power conversion efficiency of perovskite solar cells (PSCs) using a TiO2 electron transport layer, the MAPI/TiO2 interface is believed as an electron accumulation position during device operation. To elucidate the cause of the electron accumulation, the energy level alignment at the MAPI/TiO2 interface should be understood. However, a buried MAPI/TiO2 interface forms after a thick MAPI layer deposition; thus, the electronic structure of the MAPI/TiO2 interface cannot be measured using surface-sensitive photoelectron spectroscopy in a conventional stack-up manner. In this study, we investigated the electronic structure of a buried MAPI/TiO2 interface by removing the MAPI and organic layers using solvent immersion. As a result, we reveal that a conduction band minimum (CBM) mismatch occurs owing to the Ti–O–Pb bonding on the TiO2 surface. The Ti–O–Pb bonds form by the Pb ions penetrating during the spin coating of the MAPI solution. When a [6,6]-phenyl C61 butyric acid methyl ester (PCBM) layer was inserted, the CBM mismatch was removed owing to the high work function of PCBM.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physics and Astronomy(all)
- Surfaces and Interfaces
- Surfaces, Coatings and Films