A simple method with analytical model to extract heterojunction solar cell series resistance components and to extract the a-Si:H(I/P) to transparent conductive oxide contact resistivity

Abstract

Silicon heterojunction (SHJ) solar cell technology has the potential to be the next mainstream industrial solar cell design due to its high efficiency and lean production process with only four main process steps. While two-side contacted SHJ cells have very high open circuit voltages (Voc) >740 mV, they tend to be lower in short circuit current density (Jsc) and fill factor (FF). Understanding the series resistance (Rs) components of such cells is crucial as these cells have two extra TCO/a-Si/Si contact resistances due to the optically absorptive passivating electrodes. Reducing the Rs components contribution is essential to improve the FF. In this paper, we report a straightforward and simple analytical model to break down the Rs of our SHJ solar cell having >23% efficiency into its components with the aid from common characterization methods, namely transfer length method (TLM) and Cox and Strack method. We derived the silicon bulk to transparent conductive oxide (TCO) contact resistivity through the amorphous-silicon (a-Si:H) intrinsic/p-doped stacks, a parameter that is not measureable directly, from experimental SHJ solar cell results, using front-junction, rear-junction and front finger number variation setups. We found it to be 0.30 ± 0.07 Ωcm2. Further reducing this value is one of the keys to improve SHJ solar cell's FF.