Tunable TiO2–pepsin thin film as a low-temperature electron transport layer for photoelectrochemical cells

Abstract

Electron transport layer (ETL) in perovskite-based solar cells (PSCs) is attractive from the perspective of photon-to-electron conversion efficiency. TiO2 thin film is preferred in situations where microstructure, stability and charge transport characteristics are important. In this regard, we illustrate an approach that involves the synthesis of TiO2–pepsin thin film that can be used either as a mesoporous or compact layer depending on the device architecture of PSC devices. It was observed that pepsin acts as organic glue to TiO2 nanoparticles and facilitates in controlling morphology of the thin film. The addition of pepsin did not have any adverse effect on TiO2 anatase phase. Thickness and roughness of mesoporous and compact TiO2 thin film suggested that controlled agglomeration can be achieved by tuning the concentration of pepsin in the precursor colloidal solution. The spin-coated thin films indicated high bulk mobility (205 cm2 V−1 s−1) and good thermal stability over a wide range temperature (25–700°C). Furthermore, in the presence of pepsin group in TiO2 thin film, the inherent optical properties were retained, as confirmed by UV–vis analysis.