Study of MgCl 2 activation treatment on the defects of CdTe solar cells by capacitance-voltage, drive level capacitance profiling and admittance spectroscopy techniques

Abstract CdTe solar cells have recently reached its highest conversion efficiencies, comparable to CuInGaSe 2 and Si devices. One of the key factors for the success of these devices is the so-called “activation” treatment, which typically consists in depositing a CdCl 2 film on the CdTe absorber layer and in a subsequent annealing in air or nitrogen atmosphere. Nevertheless CdCl 2 is a carcinogenic and water-soluble compound; for this reason recent studies have found MgCl 2 as a good alternative. In this work we have studied devices (exceeding 14% efficiency) prepared by low-substrate temperature CdTe deposition and activated with MgCl 2 treatment (applied by wet deposition). The devices were characterized by means of current-voltage, capacitance-voltage, drive level capacitance profiling and admittance spectroscopy techniques. Carrier concentration and also concentration and distribution of shallow and deep defects are presented and compared with data obtained from analogous devices but activated with the standard CdCl 2 . Despite CdTe layers treated with the two different processes exhibit similar structural properties, the distribution of deep and shallow defects results to be different and moreover admittance spectroscopy technique reveals the presence of different defects, at 344 and 358 meV, which are present only in MgCl 2 treatment case.