Dependence of photovoltaic parameters on grain size and density of states in n-i-p and p-i-n polycrystalline silicon solar cells

One-dimensional modeling of polycrystalline silicon (pc-Si) p⁺-i-n⁺ and n⁺-i-p⁺ homojunctions under AM1.5 light is presented. Single-crystalline grains separated by amorphous silicon transition zones are introduced to model the pc-Si structure. The usual density of states (DOS) with exponential band-tails and Gaussian-distributed deep levels is assumed in these transition regions. Effects of the grain size, the thickness of the undoped region and the DOS on the photovoltaic characteristics are presented. The calculation enables us to understand the very poor performance of the solar cells based on solid-phase-crystallized polysilicon processed at low temperature (< 600 °C). It gives the minimum value of the grain size and the maximum DOS to obtain acceptable photovoltaic performance.