Spectroscopic Ellipsometry Applied in the Full p-i-n a-Si:H Solar Cell Device Configuration

Abstract

Assessment of the performance of single-junction hydrogenated amorphous silicon (a-Si:H) p-i-n configuration solar cells has been developed with a combination of real-time spectroscopic ellipsometry (RTSE) and current-voltage (I-V) measurements. For each layer, RTSE measurements enabled the determination of thickness and optical properties in the form of the complex dielectric function (e = e 1 + ie 2 ) spectra. RTSE tracked changes in a as a function of depth and was used to extract profiles in the i-layer bandgap and crystallite fraction in the n-layer. Through mapping I-V characteristic measurements, spatial variations in device performance were determined. By comparing individual devices at the location of the RTSE beam spot, the influence of a and thickness for each layer on device performance was identified through simulations of quantum efficiency yielding the shortcircuit current. This study compares two devices prepared with different superstrate preheating processes and finds that the combination of RTSE and I-V measurements along with quantum efficiency simulations were able to identify plasma damage to the transparent conducting oxide as the likely cause for variation in device performance. This comparison serves as one example of how the optically obtained information, such as thickness and a for each layer, can be used to understand the final device performance.