The impact of charged grain boundaries on thin-film solar cells and characterization

We use two-dimensional computer simulations to examine how charged columnar grain boundaries (GBs) affect transport, recombination, characterization, and performance in polycrystalline Cu(In,Ga)Se-2 solar cells. Although the simulations show that charged GBs can increase photocurrent by forming minority-carrier collection channels, this generally occurs at the expense of overall efficiency. Carrier dynamics induced by the GBs significantly alter time-resolved photoluminescence, near-field scanning optical microscopy, electron-beam-induced current microscopy, and quantum efficiency spectra. Consequently, these experiments can place bounds on the role and strength of GB charge in polycrystalline materials. Simulations of these experiments indicate that GB charge sufficient to significantly increase photocurrent collection is generally inconsistent with the actual observations for Cu(In,Ga)Se-2 solar cells. (c) 2005 American Institute of Physics.