Tailored Band Structure of Cu(In,Ga)Se2Thin-Film Heterojunction Solar Cells: Depth Profiling of Defects and the Work Function

Ha Kyung Park, Yunae Cho, Kihwan Kim, Inyoung Jeong, Jihye Gwak, Jae Ho Yun, William Jo

Research output: Contribution to journalArticlepeer-review

6 Scopus citations


An efficient carrier transport is essential for enhancing the performance of thin-film solar cells, in particular Cu(In,Ga)Se2 (CIGS) solar cells, because of their great sensitivities to not only the interface but also the film bulk. Conventional methods to investigate the outcoming carriers and their transport properties measure the current and voltage either under illumination or dark conditions. However, the evaluation of current and voltage changes along the cross-section of the devices presents several limitations. To mitigate this shortcoming, we prepared gently etched devices and analyzed their properties using micro-Raman scattering spectroscopy, Kelvin probe force microscopy, and photoluminescence measurements. The atomic distributions and microstructures of the devices were investigated, and the defect densities in the device bulk were determined via admittance spectroscopy. The effects of Ga grading on the charge transport at the CIGS-CdS interface were categorized into various types of band offsets, which were directly confirmed by our experiments. The results indicated that reducing open-circuit voltage loss is crucial for obtaining a higher power conversion efficiency. Although the large Ga grading in the CIGS absorber induced higher defect levels, it effectuated a smaller open-circuit voltage loss because of carrier transport enhancement at the absorber-buffer interface, resulting from the optimized conduction band offsets.

Original languageEnglish
Pages (from-to)34697-34705
Number of pages9
JournalACS Applied Materials and Interfaces
Issue number30
StatePublished - 3 Aug 2022

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© 2022 American Chemical Society.


  • Cu(In,Ga)Se
  • bandgap grading
  • conduction band offset
  • solar cells
  • thin film


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