High-forward-bias transport mechanism in a-Si:H/c-Si heterojunction solar cells

• Published in: Physica status solidi. A, Applications and materials science Vol. 207; no. 3; pp. 657 - 660
• Main Authors: Schulze, T. F., Korte, L., Conrad, E., Schmidt, M., Rech, B.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Berlin WILEY-VCH Verlag 01-03-2010; WILEY‐VCH Verlag; Wiley-VCH
• Subjects: 73.40.Lq; 81.05.Gc; 84.60.Jt; 85.30.De; Applied sciences; Energy; Exact sciences and technology; Natural energy; Photovoltaic conversion; Solar cells. Photoelectrochemical cells; Solar energy; Buffer layer; Silicon solar cells; Voltage current curve; Diode; Bias; Aluminium; Charge transport; Open circuit voltage; Temperature measurement; Zinc oxide; Numerical simulation; Photoelectron spectrometry; Heterojunction
• ISSN: 1862-6300; 1862-6319
• DOI: 10.1002/pssa.200982747

In order to elucidate the transport mechanism in a‐Si:H/c‐Si heterojunction solar cells under high forward bias (U > 0.5 V), we conducted temperature‐dependent measurements of current–voltage (I–V) curves in the dark and under illumination. ZnO:Al/(p)a‐Si:H/(n)c‐Si/(n+)a‐Si:H cells are compared with inversely doped structures and the impact of thin undoped a‐Si:H buffer layers on charge carrier transport is explored. The solar cell I–V curves are analyzed employing a generalized two‐diode model which allows fitting I–V data for a broad range of samples. The fitting results are complemented with numerical simulations using AFORS‐HET under consideration of microscopic a‐Si:H parameters as determined by constant‐final‐state‐yield photoelectron spectroscopy (CFSYS) to identify possible origins for a systematic increase of the high‐forward‐bias ideality factor along with the open‐circuit voltage (Voc). It is further shown that also for a‐Si:H/c‐Si heterojunctions, dark I–V curve fit parameters can unequivocally be linked to Voc under illumination, which may prove helpful for device assessment.