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

Abstract

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 þ )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 twodiode 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-stateyield photoelectron spectroscopy (CFSYS) to identify possible origins for a systematic increase of the high-forward-bias ideality factor along with the open-circuit voltage (V oc ). It is further shown that also for a-Si:H/c-Si heterojunctions, dark I-V curve fit parameters can unequivocally be linked to V oc under illumination, which may prove helpful for device assessment.

Record Infrared Internal Quantum Efficiency in Silicon Heterojunction Solar Cells With Dielectric/Metal Rear Reflectors

“…This device had an open-circuit voltage (V oc ) of 750 mV-the highest ever reported for a single-junction crystalline silicon device and 44 mV higher than that of the record 25.0%-efficient UNSW PERL cell [2], [3]-thanks to the displacement of the metal contacts from the wafer surface enabled by amorphous silicon (a-Si:H) passivation [4], [5]. The 83.2% fill factor (FF) of the Panasonic cell was also slightly higher than that of the UNSW PERL cell, easing fears that silicon heterojunction solar cells could not reach high FFs [6]- [9]. However, the short-circuit current density (J sc ) was an enormous 3.2 mA/cm 2 lower than that of the UNSW PERL cell; had the Panasonic device duplicated Z. C. Holman is with Arizona State University, School of Electrical, Computer, and Energy Engineering, Tempe, AZ, USA (e-mail: zachary.…”