Abstract
The potential-induced degradation (PID) mechanism in Cu(In,Ga)(Se,S)2 (CIGS) thin-film solar cells, which are alternative energy sources with a high efficiency (>23%) and upscaling possibilities, remains unclear. Therefore, the cause of PID in CIGS solar cells was investigated in this study at the cell level. First, an appropriate PID experiment structure at the cell level was determined. Subsequently, PID and recovery tests were conducted to confirm the PID phenomenon. Light current–voltage (I–V), dark I–V, and external quantum efficiency (EQE) analyses were conducted to determine changes in the cell characteristics. In addition, capacitance–voltage (C–V) measurements were carried out to determine the doping concentration and width of the space charge region (SCR). Based on the results, the causes of PID and recovery of CIGS solar cells were explored, and it was found that PID occurs due to changes in the bulk doping concentration and built-in potential at the junction. Furthermore, by distinguishing the effects of temperature and voltage, it was found that PID phenomena occurred when potential difference was involved.
Highlights
Based on global photovoltaic (PV) market statistics, the global cumulative PV capacity was 591 GW in 2019 [1]
The CIGS solar cells were fabricated by using a standard method: 800 nm of Mo was deposited by direct current (DC) sputtering on soda-lime glass (SLG) substrates, followed by three-stage co-evaporation of CIGS, chemical bath deposition of 60 nm CdS, and radio frequency (RF) sputtering of 50 nm intrinsic ZnO and 250 nm indium tin oxide (ITO)
After applying a voltage to the CIGS solar cells and examining the changes of parameters, as shown in Figure 3 and Table 1, it can be seen that the efficiency (Eff) decreased significantly in a short time of 3 h when the voltage was applied like test structure I
Summary
Based on global photovoltaic (PV) market statistics, the global cumulative PV capacity was 591 GW in 2019 [1]. PID is generated as follows: when PV modules are connected in series, the module frames are grounded for safety and support reasons because a voltage > 600 V is generated. This leads to a relative potential difference between the grounded electrodes and solar cells inside the modules, which increases toward the end of the serial connection. Leakage current flows in solar cells due to the negative potential difference compared with the frame, and the power of the modules eventually decreases.
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