Simulation and optimization of n-type interdigitated back contact silicon heterojunction (IBC-SiHJ) solar cell structure using Silvaco Tcad Atlas

Abstract

Simulation models of interdigitated back contact silicon heterojunction (IBC-SiHJ) solar cells, not only help in understanding the cell behavior in line with the experimental results but also help further in predicting the cell performance, adding to the cost effectiveness in the cell processing.IBC-SiHJ solar cells that combine the hydrogenated amorphous silicon/crystalline silicon (a-Si:H/c-Si) heterojunction and interdigitated back contact (IBC) concepts are very promising in order to reach the highest one-junction efficiency (η). In this paper, we have studied these solar cells by two dimensional modeling using Silvaco Tcad Atlas software which has recently extended its capability to simulate these devices and given accurate bulk and interface complex defect models and allowed special specification of transport physics for the hetero-interface. The study has been done on the IBC-SiHJ structure based on n-type crystalline silicon (c-Si) by introducing a very thin intrinsic hydrogenated amorphous silicon (i-a-Si:H) layer between the c-Si base and the doped a-Si:H layers and varying the values of the following parameters: c-Si substrate and back-surface field (BSF) doping concentration, thickness of i-a-Si:H layer (Thi-a-Si) and rear side geometry. The impact of these parameters has been tested by generating the current–voltage characteristics under illumination. It is shown that the open circuit voltage (VOC) and η of IBC-SiHJ solar cells increase with decreasing i-a-Si:H thickness. The η improves further with the increase of p-type emitter width (2Wp), the decrease of n-type BSF width (2Wn) and gap width (Wg) which are explained by the simulation. The S-shaped J–V curves with low fill factor (FF) observed previously in experiments are confirmed by simulation. To improve FF, Thi-a-Si and Wg should decrease. Results indicate that to achieve high η, c-Si substrate and BSF doping concentration must be optimized. The Wg (spacing between BSF and the emitter) must be kept as small as possible to avoid recombination of minority carriers in the base. The optimum geometry corresponds to a minimum size BSF region and a maximum size emitter region. With these optimizations, an enhanced η 23.20% is demonstrated by the simulation.