Passivating Surface Defects and Reducing Interface Recombination in CuInS2 Solar Cells by a Facile Solution Treatment

TL;DR

This study demonstrates that a simple sulfur-based solution treatment effectively passivates interface defects in CuInS2 solar cells, reducing recombination and improving open-circuit voltage, thereby enhancing device efficiency.

Contribution

It introduces a facile sulfur-based post-deposition treatment that passivates interface defects and reduces recombination in CuInS2 solar cells, improving their voltage performance.

Findings

Significant reduction in VOC deficit after S-PDT.

Increased activation energy indicating reduced interface recombination.

Reduction of slow metastable defects in treated devices.

Abstract

Interface recombination at the absorber buffer interface impedes the efficiency of a solar cell with an otherwise excellent absorber. The internal voltage or the quasi-Fermi level splitting (qFLs) measures the quality of the absorber. Interface recombination reduces the open circuit voltage (VOC) with respect to the qFLs. The present work explores a facile sulfur-based post-deposition treatment (S-PDT) to passivate the interface of CuInS2 thin films grown under Cu-rich conditions, which show excellent qFLs values, but much lower VOCs. The CuInS2 absorbers are treated in three different S-containing solutions at 80 oC. Absolute calibrated photoluminescence and current-voltage measurements demonstrate a reduction of the deficit between qFLs and VOC in the best S-PDT device by almost one third compared to the untreated device. Analysis of temperature dependence of the open-circuit voltage shows increased activation energy for the dominant recombination path, indicating less interface recombination. In addition, capacitance transient measurements reveal the presence of slow metastable defects in the untreated solar cell. The slow response is considerably reduced by the S-PDT, suggesting passivation of these slow metastable defects. The results demonstrate the effectiveness of solution based S-treatment in passivating defects, presenting a promising strategy to explore and reduce defect states near the interface of chalcogenide semiconductors.