The synthesis of titania thin films used in the assembly of dye‐sensitized solar cells requires high temperature Cross-section (a) of annealed papain/titania layer deposited on indium tin oxide-coated glass showing a minimum thickness of 170 nm and a maximum thickness of 520 nm. Surface of the annealed layer (b) on coated glass. Source: Edward F. van Amelrooij et al.processing and expensive equipment. Researchers have been fruitful in devising a low-cost, simpler production route that makes use of papain, an enzyme found in the papaya.

The enzyme is applied to indium tin oxide and other substrates in a dip coating process and subjected to mild heating conditions. Thin layers of papain were demonstrated to catalyze the titania mineralization process and were then removed in a low-temperature evaporation process. The approach enables stacking of papain/titania layers to yield hybrid enzyme/titania multilayer thin films.

The highly porous nature of the titania layers, which is of value in increasing solar cell efficiency, was confirmed by positron annihilation spectroscopy.

The researchers from Delft University of Technology (The Netherlands), Bundeswehr University Munich (Germany) and Technical University of Munich (Germany) combined the enzymatically synthesized titania layers with a natural dye and a water-based electrolyte solution to build a sustainable, low‐cost solar cell. Continuing development of the production process described in Advanced Sustainable Systems will focus on increasing solar cell performance and stability by using different dyes and by tuning the porosity of the titania layers.