TiO2/ZnO double-layer broadband antireflective and down-shifting coatings for solar applications

Making full use of sunlight in solar cells requires reducing the reflection of light and minimizing spectral mismatch. Here, a TiO2/ZnO double-layer coating with both wider band antireflection and down-shifting performance was prepared. TiO2 sols and ZnO nanoparticles were synthesized via the sol-gel method and then successively coated on the surface of the Si substrate by dip-coating. Computational simulations were used to obtain the optimal refractive index and thickness of the coatings. In the experiments, the thicknesses of the TiO2 and ZnO coatings were adjusted by changing the lifting speed, and the refractive index of the TiO2 and ZnO coatings were adjusted by adding the porosity inducing agent and varying the concentration of the solution. The TiO2/ZnO coating reduces the reflectivity of the silicon substrate by 24.97% in the 400–1100 nm band, and the ZnO nanoparticles can convert light at approximately 345 nm–527 nm, reducing the spectral mismatch of the solar cell. The photocurrent of solar cells coated with TiO2/ZnO coatings was markedly improved, with an increase of 29% in the average photocurrent at 300–800 nm. Herein, TiO2/ZnO coatings have the potential to benefit the development of multifunctional coatings that are important for improving the efficiency of solar cells.