High Efficiency Interdigitated Front Contact Crystalline Si Solar Cells with Ion Implanted Back Surface Field

Abstract: We have fabricated novel interdigitated front contact structure silicon solar cells by using CMOS process technologies. In order to reduce back surface recombination, we have studied low energy ion-implanted P+ and N+ back surface field (BSF). With N+ BSF layer, Voc and the efficiency of the solar cells increased on average by 30mV and 1.3％, respectively. N+ BSF layer reduced recombination at the back surface significantly while P+ layer increased it. The higher Voc due to the reduced recombination for the N+ BSF and the lower Voc due to the increased recombination for the P+ BSF were attributed to the asymmetry in the capture cross-sections of the minority carriers (σn ~ 100*σp). In order to reduce light shading of front metal grids down to 4％, we developed trapezoidal metal etching technology. Self-aligned spacer technology was used for isolation between emitter and base local contacts. Shallow emitter junction was formed by ion implantations and low leakage barrier metal contacts were developed. And we adjusted these with fine pattern interdigitated grids. Inverted pyramid texturing and double anti-reflection coating were integrated to increase photo absorption. We adopted semiconductor package technology for mobile module fabrication. By integrating new cell and module technologies, we have recorded maximum module efficiency of 20.1％ in our R＆D laboratory.

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