Probing the arsenic distribution and dopant activation in poly-crystalline CdTe1−xSex solar cell absorbers

Abstract

We examine the arsenic distribution and its influence on dopant activation in poly-crystalline CdTe1−xSex solar cell absorbers prepared by vapor transport deposition followed by CdCl2 annealing. For as-deposited CdTe:As, local-electrode atom probe (LEAP) tomography reveals non-uniform distributions of arsenic clusters in the top “doped” layers. Following CdCl2 annealing, secondary ion mass spectrometry suggests that arsenic has diffused into the entire CdTe layer, while LEAP tomography reveals dissolution of the clusters, with nearly uniform distribution of arsenic atoms in CdTe. Since the arsenic fraction (fAs) is 1 × 1018 cm−3, but the hole density ranges from 7.5 to 9.5 × 1015 cm−3, we hypothesize that a large fraction of the arsenic has been incorporated into interstitial sites or cadmium substitutional sites, resulting in limited dopant activation.