Cruz, A.; Neubert, S.; Morales-Vilches, A.B.; Erfurt, D.; Körner, S.; Ruske, F.; Stannowski, B.; Szyszka, B.; Schlatmann, R.: Optoelectronic Performance of TCO on Silicon Heterojunction Rear-Emitter Solar Cells. In: Proceedings : EU PVSEC 2018, 35th European Photovoltaic Solar Energy Conference and Exhibition : 24-28 September 2018, SQUARE - Brussels Meeting Centre, Brussels, Belgium. EUPVSEC, 2018. - ISBN 3-936338-50-7, p. 452-455
10.4229/35thEUPVSEC20182018-2DO.2.2

Abstract:
When designing silicon heterojunction (SHJ) solar cells with a rear-emitter (RE) configuration the requirements of the conductivity of the transparent conducting oxide (TCO) at the front side are relaxed due to the contribution of lateral current flow within the silicon wafer. In this study, we analyze two approaches that can be implemented to benefit from this. Firstly, the absorption of the TCO can be reduced by designing a thinner TCO layer than the single-layer anti-reflective optimum. In this case, a second anti-reflecting coating has to be deposited on top of the TCO to minimize reflection losses. Secondly, less conductive and more cost-effective materials can be used without strongly compromising the device’s series resistance Rs and FF and, hence, the cell performance. To quantify the optoelectronic potential of these approaches in detail, we performed a comparative study of three different TCOs: indium tin oxide (ITO), aluminum doped zinc oxide (ZnO:Al), and hydrogenated indium oxide (IO:H) on rear-emitter SHJ solar cells. From simulations and experimental results, we conclude that, as expected, solar cells with IO:H as the front TCO reach the higheest efficiency. However, low-cost and higher resistive materials such as ZnO:Al can be implemented, without having a mayor efficiency penalty making them, moreover, competitive to the mainstream used ITO.