New evaluation technique for thin-film solar cell back-reflector using photothermal deflection spectroscopy

We report a new technique to determine the optical loss of a thin-film solar cell back-reflector using photothermal deflection spectroscopy (PDS). We modified a conventional PDS technique to measure the reflection loss of highly reflective and highly textured back reflector surfaces. PDS has demonstrated its advantages in such measurements because, unlike conventional reflectance measurements, it measures the fraction of the light that is converted to heat. We then used this technique for developing new back-reflectors. We developed a hot-Ag/cold-Ag two-layer system in which the texture is provided by the bottom Ag layer deposited at high temperature and low deposition rate, and the reflectance is provided by the top Ag layer deposited at low temperature and high deposition rate. Such a highly reflective and highly textured back-reflector system enhanced the quantum efficiency (QE) of a-Si solar cells both in the red and in the blue regions