Tunable Carrier Concentration of NaF‐Treated CIGS Solar Cells Using Heat–Light Soaking and Subsequent Heating

Abstract

The combined effect of the heat–light soaking (HLS) and subsequent heat‐soaking (HS) processes is investigated on NaF‐free and NaF‐treated CIGS solar cells with CdS buffer layer. The HLS treatment improves cell efficiency slightly with increased open‐circuit voltage for NaF‐treated CIGS solar cells, whereas the cell efficiency deteriorates for NaF‐free CIGS solar cells. The different behaviors between both types of solar cells may be due to a Na‐containing new layer, which is formed at the CIGS surface region by NaF‐treatment. On the other hand, the short‐circuit current density ( J SC ) decreases for both types of solar cells after HLS treatment, which is attributed to the extremely high carrier concentration ( N CV ), leading to a narrower space charge region. However, it is found that the large N CV can be tuned to an appropriate value using the subsequent HS technique. As a result, the J SC loss is successfully reduced, therefore improving cell efficiency. The details of this improved efficiency are discussed with respect to the change of N CV in CIGS solar cells by the HLS and HS processes.