MULTI-SCALE SIMULATION OF GRAIN BOUNDARY STRUCTURE EFFECTS IN POLY-Si THIN FILM SOLAR CELL

Abstract

The atomic structures of grain boundary (GB) and their effect on the performance of poly- Si thin film solar cell are studied by multi-scale simulations. First, the atomic structures of various GBs are calculated using molecular dynamics. Subsequently, the energy band diagram are obtained by ab-initio calculations. Then, finite difference method is performed to obtain solar cell performance. The results show that the Σ5 (twist) GB can greatly enhance the carriers recombination and results in small short-circuit current density (J SC ) and open-circuit voltage (V OC ). However, the Σ17 (twist and tilt) GBs have little influence on the cell performance. Also revealed in the simulations is that the GB near the p–n junction leads to very small J SC and V OC . When the distance between GB and p–n junction increases from about 1.10 μm to 3.65 μm, the conversion efficiency increases by about 29%. The thickness effect of solar cell containing the Σ5 (twist) GB on the cell performance is also studied. The results show that the conversion efficiency and J SC increase rapidly as the thickness increases from about 5.2 μm to 40 μm. When the thickness ranges from about 40 μm to 70 μm, the efficiency and the J SC both increase gradually and reach their own peak values at about 70 μm. When the thickness exceeds 70 μm, the efficiency and J SC both decrease gradually. However, the V OC keeps increasing with increase in thickness. The effects of GB on the carrier transport and recombination processes are discussed to understand the above results.