Improvement in performance of Si-based thin film solar cells with a nanocrystalline SiO2–TiO2 layer

• High-transmittance and self-cleaning nano-sized SiO2–TiO2 films are prepared.
• Using SiO2–TiO2 film can increase average transmittance from 90.5% (glass) to 93.6%.
• The SiO2–TiO2 films have naturally hydrophilicity with water contact angles < 13°.
• Cells with the film have a 4.9% higher photocurrent than cells without the film.

In this paper, titanium dioxide (TiO2) solution with grain sizes of 1–5 nm is prepared by microwave hydrothermal synthesis, and then mixed with silicon dioxide (SiO2) solution to yield different SiO2/TiO2 ratios. The mixed solution is then sol–gel spin-coated on glass as an anti-reflecting and self-cleaning bi-functional layer. The experimental results show that the transmittance is optimized not only by minimizing the reflectance by reflective index matching at the glass/air interface, but also by improving the film/glass interface adhesion. Adding SiO2 into TiO2 in a weight ratio of 5 leads to the highest average transmittance of 93.6% which is 3% higher than that of glass. All of the SiO2–TiO2 films exhibit a remarkable inherent hydrophilicity even when not illuminated by ultra-violet light. Using the optimized SiO2–TiO2 film in a hydrogenated amorphous silicon/microcrystalline silicon tandem, solar cell increases its conversion efficiency by 5.2%. Two months of outdoor testing revealed that cells with the SiO2–TiO2 film avoid 1.7% of the degradation loss that is caused by dust and dirt in the environment.