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Keywords:

  • CIGS solar cell;
  • heterojunction;
  • photoluminescence;
  • photovoltaic effect;
  • time-resolved photoluminescence

A series of studies on photoluminescence (PL) and time-resolved PL in Cu(In,Ga)Se2 (CIGS) solar cells is presented with emphasis on the photovoltaic effect in the ZnO/CdS/CIGS heterostructure. The photovoltage created by an excitation light increases PL yield and PL decay time of the near-band-edge PL of the CIGS absorber layer in the CIGS solar cell. Under the open circuit condition, the photovoltage reduces the carrier separation field in the space charge region. This reduces the collection of photoexcited carriers, which results in the high PL yield and long PL decay time. The two-dimensional PL intensity mapping of the CIGS solar cell reflects the photovoltage distribution, and the results are compared with the light-beam-induced current image. PL characterization of the CIGS solar cell process has been studied. A chemical-bath deposition of the CdS buffer layer and the following sputter-deposition of the high-resistivity ZnO buffer layer do not change PL intensity and PL decay time of the CIGS layer. On the other hand, a metalorganic chemical vapor deposition (MOCVD) of the high-resistivity ZnO layer leads to high PL intensity and the long PL decay time. The result is discussed in terms of the thermal diffusion of Cd from CdS layer into the CIGS absorber layer during the MOCVD process at an elevated temperature. The formation of the buried pn junction in the CIGS layer due to the Cd-diffusion is discussed in terms of an electron-beam induced current measurement. The utilization of PL as a measure of the junction formation is discussed.