Light induced degradation of Cu(In,Ga)Se2 thin film surfaces

Abstract

We investigate light-induced degradation of Cu(In,Ga)Se2 (CIGSe) layers by means of time-resolved photoluminescence (TRPL) measurements. Illumination in the range of minutes with 1 sun white light equivalent leads to a strong reduction of the carrier lifetime as determined by TRPL. Ambient storage in the dark, however, does not cause degradation. X-ray photoelectron spectroscopy of the CIGSe surface reveals a light induced enhancement of Na 1s and O 1s core-level emission. The position of the O 1s peak at 531.6 eV is related to a Na-O-CIGSe bonding complex. The light-induced degradation of the CIGSe layer finally translates into inferior open circuit voltages due to the dominance of interface recombination in completed solar cell devices. This study has implications for laboratory research and may need to be regarded in CIGSe module production.

High‐performance low bandgap thin film solar cells for tandem applications

“…The activation energy given by the open‐circuit voltage extrapolated to 0 K is comparable to the bandgap for each cell as shown in Figure , indicating that the dominant recombination path is in the bulk of these absorbers . The extrapolated activation energies at 0 K show slightly higher values compared to the bandgap extracted from EQE because of an expected 75 meV additional activation energy accounting for the temperature‐dependent thermal velocity and effective density of states indicated in and reported in as well. To identify the defects present in these cells, admittance measurements at 0 V bias voltage were performed in the dark after keeping the samples in the dark at room temperature overnight.…”

Impact of air‐light exposure on the electrical properties of Cu(In,Ga)Se2 solar cells

“…One sample was stored as reference also in air but in darkness. In consequence, all bare CIGSe layers stayed for the identical duration in ambient air and differ only in the yielded light dose; for more details, see Hölscher et al After the ALE, the samples were directly covered with CdS and stored in N 2 and darkness until sputtering a 50‐nm intrinsic and 350‐nm Al‐doped ZnO layer. For electrical characterization, a Ni/Al/Ni metal grid was evaporated on top of the layer stack.…”

“…Recently, we reported on the effect of air‐light exposure (ALE) on the apparent decay time of time‐resolved photoluminescence (TRPL) measured on bare CIGSe layers . The TRPL decay time was found to strongly degrade upon ALE.…”

“…The TRPL decay time was found to strongly degrade upon ALE. While the effect of light degradation of TRPL decay times has been known since long, the requirement of combined air and light exposure only recently came out to be the decisive step . In this contribution, we investigate the impact of ALE of bare CIGSe layers on the performance of completed solar cell devices.…”

Direct Nanoscale Characterization of Deep Levels in AgCuInGaSe2 Using Electron Energy‐Loss Spectroscopy in the Scanning Transmission Electron Microscope

“…Although there are multiple methods for characterizing trap electronic properties and energiese.g., deep-level transient spectroscopy (DLTS), [25] admittance spectroscopy, [26] and photoluminescence [27] -determination of the underlying physical structures that are specifically at fault is highly challenging using these techniques due to their lack of sufficient spatial and chemical resolution. For example, in wide-gap power-handling field effect structure, and chemical resolution, the origin and nature of the associated defects.…”