Improvement of bifacial heterojunction silicon solar cells with light-trapping asymmetrical bifacial structures

Abstract

Silicon heterojunction (SHJ) solar cell technology has recently made great progress in mass production. In particular, the average power conversion efficiency (PCE) of mass-produced solar cells has reached nearly 24%. However, the low short-circuit current density (Jsc), a drawback of the SHJ solar cells, has become a bottleneck limiting its further efficiency breakthrough. Therefore, an effective light trapping method is urgently needed for mass-produced SHJ solar cells. In this work, an innovative stacked mask method is developed and combined with a two-step texturing (TST) method to prepare micro-pyramid structures on the front and back side of SHJ solar cells with different pyramid bottom angles, respectively. This asymmetrical structure fabricated through stacked mask method significantly improves the light trapping effect without negative influence on the surface passivation effect. The optical and electrical properties of the SHJ solar cells with this asymmetrical structure under the front side illumination are discussed in detail. It is concluded that the smaller the bottom angle of the backside pyramid, the thinner the amorphous silicon passivation layer is required and the better the surface passivation quality is obtained. The external quantum efficiency (EQE) results demonstrate that the best bottom angle of backside pyramids corresponding to the optimum light trapping effect for the front side illumination is about 16°, which is consistent with the simulation results of the ray tracer. As for the optimal asymmetric structure, the Jsc of the mass-produced SHJ solar cell is improved by 0.36 mA/cm2 and the PCE is increased over 24%.