A combination of high-resolution electron microscopy and density-functional theory was used to study the atomic structure and electronic effects of structural defects, such as lamellar twins, stacking faults, and double-positioning twin boundaries in polycrystalline photovoltaic materials such as Si, CdTe, and CuInSe2. It was found that individual lamellar twins and stacking faults do not create deep levels in all these materials. However, areas with high density of these defects could form buried wurtzite layers that introduce a barrier to the majority carriers. Double-positioning twin boundaries, which contain dislocation cores, create deep levels in Si and CdTe. Surprisingly, however, they do not create deep levels in CuInSe2. These results may explain the fact that Si and CdTe solar cells usually require special passivation, whereas CuInSe2 solar cells do not. A further study of the passivation effects indicated that grain boundaries in Si could not be passivated completely by H alone. On the other hand, grain boundaries in CdTe could be passivated well by Cl and I.

Understanding the Defect Physics in Polycrystalline Photovoltaic Materials. Y.Yan, K.M.Jones, C.S.Jiang, X.Z.Wu, R.Noufi, M.M.Al-Jassim: Physica B, 2007, 401-402, 25-32