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.

Keywords:

• Titanium dioxide thin film
• pepsin
• electron transport layer
• photoelectrochemical cells