Impact of heat‐light soaking on potassium fluoride treated CIGS solar cells with CdS buffer layer

Abstract

In this study, the effects of light-soaking (LS), heat-soaking (HS), and combined LS and HS, that is, heat-light soaking (HLS) on potassium fluoride (KF)-treated and KF-free copper indium gallium selenide (CIGS) solar cells with CBD-CdS buffer layer were investigated. LS and HS did not change the basic solar cell parameters of CIGS solar cells when they were performed separately.In contrast, HLS improved cell efficiency with increased open-circuit-voltage for KF-treated CIGS solar cells, whereas it reduced cell performance for KF-free CIGS cells. Capacitance-voltage measurements confirmed a significantly increased carrier concentration in KF-treated CIGS solar cells, as compared to KF-free cells by HLS. X-ray photoelectron spectroscopy measurement revealed that the HLS did not change the atomic concentration of Cd, S, and O in CBD-CdS buffer layer.However, the concentration of Na atoms slightly increased at the CIGS surface region, as confirmed from SIMS measurement. It implies a possible reason for increased carrier concentration in KF-treated CIGS solar cells after HLS. Temperature-dependent current-voltage measurements suggests that HLS modify a K-containing new layer and affects cell performance.

Effect of heat‐bias soaking on cesium fluoride‐treated CIGS thin film solar cells

“…However, there are still many properties to be revealed with respect to alkali‐PDT. Recently, we reported that the cell performance of KF‐treated CIGS solar cells improved by heat‐light soaking (HLS) performed under open‐circuit condition . The HLS had a beneficial effect on the KF‐treated CIGS solar cells by improving the open‐circuit voltage ( V OC ) and fill factor (FF) .…”

“…Regarding such a beneficial effect of HLS treatment in alkali‐treated CIGS solar cells, an electric field generated in the CIGS absorber by light irradiation was suggested as a driving force for the increased N CV. Therefore, it can be assumed that the cell performance of alkali‐treated CIGS solar cells can be improved by applying a forward bias voltage instead of light irradiation. Tokyo Institute of Technology (Tokyo Tech.)…”

CuGaSe2 Thin Film Solar Cells: Challenges for Developing Highly Efficient Wide‐Gap Chalcopyrite Photovoltaics

“…Alkali‐elements in CIGSe films are also likely correlated with metastable properties, for example, light‐soaking or bias‐induced effects . CGSe cells showed no significant improvements in V oc and FF but showed an enhancement in J sc values as mentioned above (Figure ).…”

“…It should be noted here that heat‐light soaking (HLS) treatment, which is one of the techniques that effectively activates metastable acceptors in CIGSe, leads to further improvements in the V oc and FF values of CIGSe cells grown with RbF‐PDT . HLS treatment is generally known to increase the carrier concentration in CIGSe and decrease the depletion width . On the other hand, CGSe cells showed the opposite behavior to In‐containing CIGSe cells, namely, a decrease in the carrier concentration and an increase in the depletion width upon HLS treatment .…”

Metastable Behavior on Cesium Fluoride‐Treated Cu(In1–x,Gax)Se2 Solar Cells

“…This indicates that CsF‐treated CIGS solar cells are applicable to terrestrial and space applications. Furthermore, our previous studies revealed the beneficial effect of heat‐light soaking (HLS) or heat‐bias soaking (HBS) on alkali metal‐treated CIGS solar cells. These post‐treatments increased the efficiency ( η ) of solar cells by enhancing the open‐circuit voltage ( V OC ).…”