Engineering topics

Jiang, Chun-Sheng

Publications and source records attributed to Jiang, Chun-Sheng.

39 records · Page 3

DOE OSTI2022

LeTID-Affected Cells from a Utility-Scale Photovoltaic System Characterized by Deep Level Transient Spectroscopy

Photovoltaic modules from a utility-scale field experienced power loss by light- and elevated temperature-induced degradation (LeTID). Samples of one of the affected monocrystalline silicon cells were cored and extracted from the module packaging and encapsulation. One of the cell fragments was processed using a regeneration cycle of applying short-circuit-rated current in forward bias at 85 degrees C for 2 weeks, while the other fragment was kept in its outdoor-degraded LeTID state. Both samples were scribed to form 2-mm diameter isolated areas using a femtosecond-pulse-width laser micromachining system. Both isolated areas contained front grid line segments which were wire bonded to larger contact pads, and the samples were probed in a cryostat linked to a deep-level transient spectroscopy (DLTS) system. Using DLTS, a majority-carrier, hole-trap defect was detected on each sample with an activation energy of 0.42 eV. The LeTID-degraded sample, however, had a larger signal corresponding to a trap density of 1.1x10^13 cm-3, which was about five times larger than the 2.1x10^12 cm-3 trap density of the regenerated sample.

charge carrier lifetime↗

DOE OSTI2022

Investigating the Role of Copper in Arsenic Doped CdSeTe Photovoltaic Devices

As part of NREL's development of arsenic doped CdSeTe devices, co-doping with copper has become a common practice and, despite little difference in carrier concentration (often ~1016 cm-3), co-doped devices regularly show improved Voc. Given the critical importance of improving Voc, we are investigating this trend with a wide variety of characterization techniques including SEM, EBSD, SIMS, PL, CL, XPS, TRPL, JVT, KPFM, and DLTS. Together these indicate that Cu facilitates improved absorber-buffer interface properties and potentially improved bulk absorber characteristics, though specific mechanisms have not yet been determined. Despite the improved performance of co-doped devices, Voc is still far below its potential, and we explore the possibility that this limitation is the result of low buffer doping in conjunction with high absorber doping.

arsenic doping↗

DOE OSTI2022

Investigating the Role of Copper in Arsenic Doped Cd(Se,Te) Photovoltaics

The open circuit voltage (VOC) deficit in Cd(Se,Te)-based photovoltaics remains a critical obstacle for pushing the technology closer to theoretical performance limits. Arsenic doping has become a dominant and promising route to achieve the higher p-type carrier concentrations necessary for higher VOC, but challenges associated with this alternate defect chemistry and higher doping density have hindered progress. Here we show that while arsenic doping enables high carrier concentrations (>1016 cm-3), co-doping with copper can provide a boost to VOC without a significant change to carrier concentration. A large data set is initially used to explore current-voltage and capacitance-voltage trends associated with arsenic doped devices with and without copper. A smaller subset is then used to probe these trends using a wide variety of characterization techniques. Copper is found to facilitate reduced interface recombination and potentially improved bulk absorber characteristics, though the mechanisms for these improvements are not yet clear. Despite the improved performance of co-doped devices, VOC is still far below its potential especially for highly doped devices. Low emitter doping in conjunction with high absorber doping seems to be a plausible cause for this significant deficit, though other device properties may exacerbate this problem.

CdSeTe↗