Effect of variation of thickness of TiO₂ on the photovoltaic performance of n-TiO₂/p-Si heterostructure

Fabrication of heterojunctions of Si along with oxide based semiconductors like TiO₂ is an alternative method to produce cost effective solar cells. To study the photovoltaic performance of the n-TiO₂/p-Si heterostructure, TiO₂ thin films of different thicknesses were deposited on p type Si substrates using pulsed laser deposition technique. All the films were characterized using XRD, AFM, Spectroscopic ellipsometry and I–V characteristics with solar simulator and other monochromatic light sources of different wavelengths. Optical properties of the thin films were correlated with the I–V characteristics under dark and illumination conditions. It has been shown that thickness plays a crucial role on the photovoltaic performance of the n-TiO₂/p-Si heterostructure. Further, it has been observed that the optical reflectivity of TiO₂ thin film of particular optimized thickness deposited on p type Si could be lowest. Consequently, photocurrent of the n-TiO₂/p-Si heterostructure is found to decrease with an increment of the thickness of the TiO₂ thin film. This is attributed to the increment of series and sheet resistance with increase of TiO₂ film thickness. Moreover, increase of TiO₂ film thickness can also create surface states and defects in the n-TiO₂/p-Si heterojunction which are also responsible for poor efficiency of the photovoltaic cells.