Microstructural dependence of electron and hole transport in low-temperature-grown polycrystalline-silicon thin-film solar cells

Abstract

Carrier transport properties of undoped polycrystalline silicon (poly-Si) thin films prepared by SiH4–H2 plasma at low temperature have been investigated. The ac-conductivity measurement technique has been applied to poly-Si i layers with an n-i-n junction structure in order to characterize the electron conductivity along the growth direction. Furthermore, the hole conductivity has been measured with p-i-p junction structures. The temperature dependence of ac conductivity reveals that poly-Si films with relatively low crystalline volume fraction (Xc∼50%) exhibit intrinsic character, while the poly-Si films with high Xc (>50%) exhibit n-type character with activation energies less than 0.15 eV. Based on these results, the relationship among microstructure, carrier transport, and photovoltaic performance of poly-Si solar cells is discussed.