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

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 SiNx 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 SiNx (n = 2.1) passivated solar cells. Furthermore, it is shown that the efficiency of SiNx (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 SiNx layer (characterized by the n value), and the thicknesses of SiNx 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 SiNx(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/SiNx stack is capped with mesoporous TiO2. These efficiencies are 0.24 and 1.25% higher, respectively, when compared to the original SiNx passivated PERC solar cell, demonstrating the prospective of using TiO2 in encapsulant-free commercial photovoltaic applications.