THREE-DIMENSIONAL NUMERICAL ANALYSIS OF HYBRID HETEROJUNCTION SILICON WAFER SOLAR CELLS WITH FRONT-SIDE LOCALLY DIFFUSED EMITTER AND REAR-SIDE HETEROJUNCTION BSF POINT CONTACTS

摘要

This paper presents a three-dimensional numerical analysis of a hybrid homojunction/heterojunctionsilicon wafer solar cell, featuring: (ⅰ) a front-side locally diffused emitter, enabling a higher short-circuit currentcompared to a pure heterojunction concept and (ⅱ) rear-side heterojunction back surface field point contacts, enablinga higher open-circuit voltage compared to a pure homojunction concept. Two different types of heterojunction pointcontacts are investigated and compared to the corresponding full-area heterojunction contacts, (ⅰ) using aconventional heterojunction a-Si:H(i)/a-Si:H(n)/TCO/metal stack or (ⅱ) using a simplified μc-Si:H(n)/metal stack(enabling a high doping efficiency and being able to omit the TCO). Heterojunction point contacts are found to besuperior to the corresponding full-area contacts. Using the conventional heterojunction stack for point-contactformation, significantly higher solar cell efficiencies can be achieved compared to using the μc-Si:H(n)/metal stack,i.e. cell efficiencies of 22.8 % compared to 20.4 % can be expected. An optimized rear contact fraction of 7 % (orequivalently a 110 × 110 μm2 rear-contact area) is predicted, by calibrating the program against intensity dependentlifetime measurements characterizing the various passivation layers used (i.e. B-diff/AlO_x/SiN_x, SiN_x, a-Si:H(i),a-Si:H(i)/a-Si:H(n), μc-Si:H(n) passivation). Using highly conductive μc-Si:H(n)/metal point-contacts, the efficiencycan still exceed 20 %, allowing to omit the usage of the transparent conductive oxide layer (TCO).