A Generalized Theory Explains the Anomalous Suns– Voc Response of Si Heterojunction Solar Cells

by Raghu Vamsi Krishna Chavali, Jian V Li, Corsin Battaglia, Stefaan De Wolf, Jeffery Lynn Gray, Muhammad Ashraful Alam
Year: 2017 DOI: 10.1109/JPHOTOV.2016.2621346


Chavali, Raghu Vamsi Krishna, Jian V. Li, Corsin Battaglia, Stefaan De Wolf, Jeffery Lynn Gray, and Muhammad Ashraful Alam. "A Generalized Theory Explains the Anomalous Suns–Voc Response of Si Heterojunction Solar Cells." IEEE Journal of Photovoltaics 7, no. 1 (2017): 169-176.


​Suns-Voc measurements exclude parasitic series resistance effects and are, therefore, frequently used to study the intrinsic potential of a given photovoltaic technology. However, when applied to a-Si/c-Si heterojunction (SHJ) solar cells, the Suns-Voc curves often feature a peculiar turnaround at high illumination intensities. Generally, this turn-around is attributed to extrinsic Schottky contacts that should disappear with process improvement. In this paper, we demonstrate that this voltage turnaround may be an intrinsic feature of SHJ solar cells, arising from the heterojunction (HJ), as well as its associated carrier-transport barriers, inherent to SHJ devices. We use numerical simulations to explore the full current-voltage (J-V) characteristics under different illumination and ambient temperature conditions. Using these characteristics, we establish the voltage and illumination-intensity bias, as well as temperature conditions necessary to observe the voltage turnaround in these cells. We validate our turnaround hypothesis using an extensive set of experiments on a high-efficiency SHJ solar cell and a molybdenum oxide (MoOx) based hole collector HJ solar cell. Our work consolidates Suns-Voc as a powerful characterization tool for extracting the cell parameters that limit efficiency in HJ devices.​


Suns-Voc Heterojunction Solar Cells numerical simulations