Determination of Grain Boundary Charging in Cu(In,Ga)Se2 Thin Films

C. S. Jiang, M. A. Contreras, I. Repins, H. R. Moutinho, R. Noufi, M. M. Al-Jassim

Research output: Contribution to conferencePaperpeer-review

7 Scopus Citations


Surface potential mapping of Cu(In,Ga)Se2 (CIGS) thin films using scanning Kelvin probe force microscopy (SKPFM) aims to understand the minority-carrier recombination at the grain boundaries (GBs) of this polycrystalline material by examining GB charging, which has resulted in a number of publications. However, the reported results are highly inconsistent. In this paper, we report on the potential mapping by measuring wide-bandgap or high-Ga-content films and by using a complementary atomic force microscopy-based electrical technique of scanning capacitance microscopy (SCM). The results demonstrate consistent, positively charged GBs on our high-quality films with minimal surface defects/charges. The potential image taken on a low-quality film with a 1.2-eV bandgap shows significantly degraded potential contrast on the GBs and degraded potential uniformity on grain surfaces, resulting from the surface defects/charges of the low-quality film. In contrast, the potential image on an improved high-quality film with the same wide bandgap shows significantly improved GB potential contrast and surface potential uniformity, indicating that the effect of surface defects is critical when examining GB charging using surface potential data. In addition, we discuss the effect of the SKPFM setup on the validity of potential measurement, to exclude possible artifacts due to improper SKPFM setups. The SKPFM results were corroborated by using SCM measurements on the films with a CdS buffer layer. The SCM image shows clear GB contrast, indicating different electrical impedance on the GB from the grain surface. Further, we found that the GB contrast disappeared when the CdS window layer was deposited after the CIGS film was exposed extensively to ambient, which was caused by the creation of CIGS surface defects by the ambient exposure.

Original languageAmerican English
Number of pages6
StatePublished - 2012
Event38th IEEE Photovoltaic Specialists Conference, PVSC 2012 - Austin, TX, United States
Duration: 3 Jun 20128 Jun 2012


Conference38th IEEE Photovoltaic Specialists Conference, PVSC 2012
Country/TerritoryUnited States
CityAustin, TX

Bibliographical note

See CP-5200-54111 for preprint

NREL Publication Number

  • NREL/CP-5200-56911


  • CIGS
  • grain boundary
  • scanning capacitance microscopy
  • surface potential scanning Kelvin probe force microscopy


Dive into the research topics of 'Determination of Grain Boundary Charging in Cu(In,Ga)Se2 Thin Films'. Together they form a unique fingerprint.

Cite this