Quantum efficiency enhancement in multi-junction solar cells with spectrally selective and conducting 1D photonic crystals

摘要

Herein quantum efficiency enhancements are demonstrated in multi-junction solar cells with one-dimensional Selectively Transparent and Conducting Photonic Crystal (STCPC) intermediate Bragg reflectors. Specifically, the modelling, design and fabrication of series-connected multi-junction cells comprising a top amorphous-silicon cell and a bottom crystalline-silicon heterojunction cell with spectrally tunable STCPC intermediate reflectors (IR) is presented. Wave-optics modeling analysis shows current density gains of up to 17.4% and 10.4% compared to multi-junction cells without an IR and with an industry standard IR comprising a ZnO film, respectively. Fabricated multi-junction cells based on these modelled structures demonstrate that the STCPC IR enhances cell currents by 17.1% and 13.2% compared to the reference cases without an IR and with a ZnO film IR, respectively. From an efficiency standpoint, the STCPC IR improved cell performance by 7.9% over reference cells without an IR, but was 8.9% less efficient relative to the reference cells with a ZnO IR. The lower overall efficiency of the tandem cell with the STCPC IR with respect to that of the cell with the ZnO IR is primarily due to non optimal electrical performance of the STCPC compared to the single ZnO layer. Methods for improving the electrical properties are discussed.