Thin crystalline silicon solar cells with metallic back reflector

Thin-film crystalline silicon (c-Si) solar cells have the potential for very high efficiency through high open circuit voltage (Voc) [1]. The best performance reported in thin-film crystalline silicon solar cells with absorber thickness below 20 microns is 16.9% efficiency for a solar cell grown epitaxially on a crystalline silicon conductive substrate [2]. The efficiency potential of thin c-Si solar cells is above 20%. In previously reported thin c-Si solar cells, layers of porous silicon have been included as a Bragg reflector in the light trapping design or as a separation layer in the mechanical design [3, 4]. The Bragg reflector uniformity and reliability has been analyzed [5]. The challenges of this Bragg reflector are uniformity and the maximum achievable optical gain. This work presents a systematic approach to the design, fabrication, testing and analysis of thin c-Si solar cells. Solar cell designs presented include a thin c-Si solar cell with no light trapping structures and a thin c-Si solar cell with an optical design comprised of a metallic back reflector on the back surface and a chemical texture on the front surface. These baseline designs enable us to separately measure and localize voltage and current losses. The metallic back reflector has low electrical losses, good mechanical stability, and uniform optical properties. To optimize the baseline designs we measure open circuit voltage (Voc) and external quantum efficiency (EQE). Voc shows high material quality in the absorber layer. EQE shows an evidence of light trapping with a current gain of 3.6%.