Potential of TiO2 as a capping layer for industrial c-Si PERC solar cells

Abstract

Titanium dioxide (TiO₂) has gained popularity especially in photovoltaic applications, owing to its transparency in the visible region, and scratch resistance. In this work, the potential of TiO₂ as a capping layer for c-Si p-type SiN_x passivated emitter and rear contact (PERC) solar cells is studied through extensive optical and device simulations. The bifacial PERC solar cell model used in this study is calibrated with an experimental device having an efficiency of 22.19%. Device simulation results show that TiO₂ deposited by the mesoporous technique outperforms atmospheric pressure chemical vapor deposition (APCVD) and atomic layer deposition (ALD)-based TiO₂ layers when capped over SiN_x (n = 2.1) passivated solar cells. Furthermore, it is shown that the efficiency of SiN_x (n = 2.1)/TiO₂ based solar cells is maintained, even when the TiO₂ layer thickness varies from 75 to 95 nm. To enhance the efficiency further, the type of SiN_x layer (characterized by the n value), and the thicknesses of SiN_x and TiO₂ layers are optimized simultaneously to find the best combination of these parameters. The best front side solar cell efficiency of 22.43%, is obtained when a stack of SiN_x(n = 1.99)/TiO₂ (t = 58/76 nm) is used. Similarly, a rear side efficiency of 16.59% is achieved when the rear side Al₂O₃/SiN_x stack is capped with mesoporous TiO₂. These efficiencies are 0.24 and 1.25% higher, respectively, when compared to the original SiN_x passivated PERC solar cell, demonstrating the prospective of using TiO₂ in encapsulant-free commercial photovoltaic applications.