In both PIN-type and NIP-type thin film silicon solar cells, textured light trapping substrates are used to enhance light absorption and improve energy conversion efficiencies. Scalar scattering theory is used to simulate the light trapping performance of textured substrates. The results indicate that in order to get good light trapping performance, the root mean square (RMS) for front reflectors in PIN-type solar cells should be at least 160 nm, while it is only 40 nm for back reflectors in NIP-type solar cells. A series of a-SiGe:H single-junction solar cells is deposited on back reflectors with different RMS values. It is found that a-SiGe:H solar cells deposited on back reflectors with RMS values of 40 and 61.5 nm demonstrate similar short current density values and quantum efficiencies. These results indicate that RMS value of 40 nm is enough to get good light trapping performance, which is consistent with the numerical simulation.