Improvements in the amorphous silicon single junction solar cells stabilized performance can be realized by developing more stable material as well as more efficient light trapping. The optical losses of thin solar cells are investigated numerically and experimentally. New approaches involving planar junctions and diffuse rear reflectors are developed. It is theoretically possible to achieve short circuit currents over 17 mA/cm2 with a 150 nm i-layer using a diffuse rear reflector when an appropriate rear window material is employed.