Wide-gap thin film Si n-i-p solar cells deposited by hot-wire CVD

Abstract

High-voltage wide bandgap thin-film Si n-i-p solar cells have been made using the hot-wire chemical vapor deposition (HWCVD) technique. The best open-circuit voltage (V/sub oc/) has exceeded 0.94 V in solar cells using HWCVD in the entire n-i-p structure. A V/sub oc/ of 0.97 V has been achieved using HWCVD in the n and i layers and plasma-enhanced (PE) CVD for the p layer. The high voltages are attributed to the wide-gap i layer and an improved p/i interface. The wide-gap i layer is obtained by using low substrate temperatures and sufficient hydrogen dilution during the growth of the i layer to arrive at the amorphous-to-microcrystalline phase transition region. The optical band gap (E/sub o4/) of the i layer is found to be 1.90 eV. These high-voltage cells also exhibit good fill factors exceeding 0.7 with short-circuit-current densities of 8 to 10 mA/cm/sup 2/ on bare stainless steel substrates. We have also carried out photoluminescence (PL) spectroscopy studies and found a correlation between V/sub oc/ and the PL peak energy position.