Opto-Electronics Review

Abstract

Effects of temperature variation on the performance of silicon heterojunction solar cells are studied using opto-electrical simulations. It is shown that the low-temperature cell efficiency is determined by the fill factor, while at high temperatures it depends on the open-circuit voltage. Simulations revealed that the low-temperature drop in the fill factor is caused by poor tunnelling, in particular at the ITO/p-a-Si:H heterojunction. The authors link this drop in fill factor to a low maximum-power-point voltage and show how poor tunnelling is reflected in the charge redistribution determining the device voltage. The effect of the contact work function on temperature behaviour of efficiency by varying the electron affinity of ITO layers has been demonstrated. It was also demonstrated that increasing the electron affinity of ITO on the p-side minimises the work function mismatch, leading to significant improvements in efficiency, especially at low temperatures, while optimisation on the n-side results in marginal improvements over the entire temperature range. In addition to the cumulative effects of the temperature-dependent parameters, their individual contributions to the efficiency were also investigated. Moreover, it was presented that the thermal energy (kT) determines the efficiency temperature behaviour, while other parameters play only a minor role. This paper shows how temperature variations affect device performance parameters.