Enhancing Low Illumination Response of SHJ Solar Cells for More Sustainable Systems: A Device Simulation Study

Abstract

In this work, we used calibrated numerical simulation models to optimize silicon heterojunction (SHJ) solar cells, with a focus principally on higher efficiency at lower illumination. The low-light analysis is important because photovoltaic (PV) modules are exposed to varied illumination conditions depending on location, weather, and climate. Recently, we have established that for lower illumination, the SHJ configuration with thin and lower-doped front p-type emitter contact is a viable option for providing higher efficiency; however, that study was only performed for a low-doped (~10¹⁵ cm⁻³) c-Si(n) absorber. In this work, we comprehensively optimized the SHJ configuration for a wide variation of absorber doping/resistivity (5 × 10¹⁴–5 × 10¹⁷ cm⁻³/9.05–0.032 Ω cm) and observed that for highly doped (~5 × 10¹⁶ cm⁻³/0.141 Ω cm) absorbers, efficiency drops for thin and low-doped p-type emitters. On the contrary, a moderate to high doped (2 × 10¹⁶–5 × 10¹⁶ cm⁻³ /0.292–0.141 Ω cm) absorber with a standard p-type emitter enhances efficiency most effectively under low light illumination, where the generated carrier density is low. Additionally, a combination of a moderate to high doped absorber, together with a doped a-Si:H(p) contact layer for an optimized front electrode workfunction, further boosts efficiency irrespective of illumination. The other advantage of our optimization is the relaxed requirements of a higher work function (WF) of the front electrode necessary for a hole-selective contact in SHJ solar cells. We achieved a remarkable 3.2% absolute increase at low illumination (0.01 suns), and a 1.4% absolute increase at 0.1 and 1.0 suns compared to an STC-optimized cell (optimized experimentally for best efficiency at 1.0 sun). This analysis suggests designing PV modules providing energy production that is slightly better matched to the actual people’s energy needs throughout the day and year.