Role of the Front Electron Collector in Rear Emitter Silicon Heterojunction Solar Cells

Front electron collectors in rear emitter hydrogenated amorphous silicon/crystalline silicon (a- Si:H/c-Si) solar cells are comprehensively investigated with the objective of increasing cell power conversion efficiency. Since such cells benefit from the lateral electron conductivity of the n-doped substrate, the electrical constraint on the front transparent conductive oxide (TCO) layer is relaxed. However, cell improvement is only expected if the front side is optimized. Here, we present our understanding of recombination losses in the front amorphous silicon layers and at the a-Si:H/ c-Si interface, which determine the short-circuit current. In addition, we show how the TCO/(n + i)a-Si:H/(n)c-Si contact has to be finely engineered to minimize the resistance for electrons to be extracted. Both points are addressed through experimental and simulation works.