Role of EV+0.98 eV trap in light soaking-induced short circuit current instability in CIGS solar cells

TL;DR

This study identifies a specific EV+0.98 eV deep level trap in CIGS solar cells as a key factor in light soaking-induced short circuit current instability, linking trap concentration to performance degradation.

Contribution

It reveals the role of the EV+0.98 eV trap in JSC degradation and distinguishes it from other traps affecting VOC stability, advancing understanding of light-induced instabilities in CIGS cells.

Findings

EV+0.98 eV trap concentration correlates with JSC reduction

Light soaking reduces depletion depth and carrier collection

Different traps influence JSC and VOC stability separately

Abstract

Light-induced instabilities/degradation in Cu(In,Ga)Se2 (CIGS) solar cells are a prevalent and urgent issue to resolve to improve performance, uniformity, and reliability. Here, mechanisms contributing to light-induced instabilities are identified focusing on an observed short circuit current (JSC) reduction. External quantum efficiency measurements before and after light soaking identified a reduction in long wavelength photon carrier collection efficiency in the CIGS absorber layer. Using deep level optical spectroscopy (DLOS), the concentration of CIGS EV+0.98 eV deep level is correlated with the amount of JSC degradation, Finally, capacitance voltage (C-V) measurements reveal light induces a large reduction in the depletion depth and reduction of carrier collection and are all correlated with the JSC reduction. Finally, the EV+0.53 eV trap concentrations are shown to correlate with VOC instability but not the JSC reduction confirming that multiple trap-induced mechanism are responsible for the light-induced instabilities.