Numerical analysis of electrical TCO / a-Si:H(p) contact properties for silicon heterojunction solar cells
In this paper we present a one-dimensional numerical simulation study concerning the electrical properties of the TCO / a-Si:H(p) / a-Si:H(i) / c-Si(n) hole contact in amorphous / crystalline silicon heterojunction (SHJ) solar cells. Simulations where performed with Sentaurus TCAD from Synopsys considering the implemented barrier tunneling model. The modification of the a-Si:H(p) / a-Si:H(i) / c-Si(n) p/n junction by the opposing TCO / a-Si:H(p) junction and its influence on the device recombination for the relevant working conditions are investigated. We demonstrate the relevance of the effective screening length in the amorphous silicon, which depends on the effective space-charge in the a-Si:H(p) and the work function mismatch at the TCO / a-Si:H(p) interface. We highlight the importance of an improved work function matching as this presents an additional degree of freedom for the design of the SHJ and is an important parameter to reach both a very high Voc and FF.