A Generalized Theory Explains the Anomalous Suns–Voc Response of Si Heterojunction Solar Cells
AuthorsChavali, Raghu Vamsi Krishna
Li, Jian V.
De Wolf, Stefaan
Gray, Jeffery Lynn
Alam, Muhammad Ashraful
KAUST DepartmentPhysical Sciences and Engineering (PSE) Division
Materials Science and Engineering Program
KAUST Solar Center (KSC)
KAUST Solar Center (KSC), King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, Saudi Arabia
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AbstractSuns–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.
CitationChavali RVK, Li JV, Battaglia C, De Wolf S, Gray JL, et al. (2017) A Generalized Theory Explains the Anomalous Suns–Voc Response of Si Heterojunction Solar Cells. IEEE Journal of Photovoltaics 7: 169–176. Available: http://dx.doi.org/10.1109/JPHOTOV.2016.2621346.
SponsorsThis work was supported in part under the U.S.–India Partnership to Advance Clean Energy-Research (PACE-R) for the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Effi- ciency and Renewable Energy, Solar Energy Technology Program, under Sub- contract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, CO, USA) and the Government of India through the Department of Science and Technology under Subcontract IUSSTF/JCERDC-SERIIUS/2012 dated November 22, 2012.
JournalIEEE Journal of Photovoltaics