Passivated contacts

This chapter reviews the theoretical background and experimentally realized passivated contacts. It presents the fundamental requirements, suppression of recombination and lossless majority carrier transport, are discussed and the experimental realizations like heterojunctions and the different semiconductor-insulator-semiconductor (SIS) and Metal-insulator-semiconductor (MIS) concepts. The fundamental requirement of electrical contacts in solar cells is the extraction of electrons and holes from the device. The chapter discusses the fundamental requirements of passivated electron and hole. one critical requirement for passivated contacts is the suppression of recombination to allow for high internal voltages. The way in which the two fundamental prerequisites of a passivated contact are solved by a silicon heterojunction (SHJ) will be discussed using the example of the transparent conductive oxides (TCO)/a-Si:H(p)/a-Si:H(i)/c-Si(n) heterojunction. The chemical passivation of the silicon surface is realized by the intrinsic a-Si:H(i) buffer layer, which has a low defect concentration and reduces the number of defect states at the a-Si/c-Si interface.