On a better estimate of the charge collection function in CdTe solar cells: Al2O3 enhanced electron beam induced current measurements

The electron beam induced current technique (EBIC) was applied to substrate configuration CdTe solar cells in order to estimate the current density loss due to incomplete charge collection. In order to improve the measurement accuracy a thin Al2O3 layer was deposited on the device cross section by atomic layer deposition. Absorption coefficients and internal quantum efficiency (IQE) of the CdTe absorber layer and device were derived from reflection and transmission measurements. An estimate for the IQE was then calculated from EBIC measurements for devices with and without Al2O3 coating. The comparison of this estimate to the measured IQE shows that the Al2O3 enhances the accuracy of the EBIC measurements. Details of the EBIC profile and an estimate for the residual IQE i.e. current loss are discussed. Finally, a tentative explanation for the improved accuracy of the Al2O3 enhanced EBIC measurement is presented.