Effects of activation treatment on the electrical properties of low temperature grown CdTe devices

CdTe has shown a significant potential for high mass production, resulting to be one of the cheapest photovoltaic technologies available. Efficiencies exceeding 17% have been obtained by the application of high temperature CdTe deposition. However a very different role of the CdCl2 activation treatment for the low and high temperature deposited CdTe is known: requiring a strong grain size enhancement only in the first case.In our labs, vacuum evaporated CdTe is typically treated by CdCl2–methanol saturated solution. Different amounts of this solution have been applied on CdTe layers. Final conversion efficiencies are ranging, depending on the different treatments, between 6 and 13%. The electrical properties of these finished devices have been studied by means of current–voltage, capacitance–voltage, drive level capacitance profiling and admittance spectroscopy in order to connect the electrical properties of the device with the different activation treatments. Admittance spectroscopy shows a different defect energy distribution depending on the applied activation treatment and drive level capacitance profiling the different doping profile. The different transport mechanisms are addressed by studying the behavior of dependence of current–voltage characteristics with temperature.

► Different amounts of CdCl2 have been used for CdTe solar cell preparation.
► Ideality factors and band gap are calculated and discussed.
► Shallow and deep defects of the different CdCl2 treated devices are addressed.
► Different doping profiles are observed and explained.
► Different treatments dramatically change the doping profiles and nature of the defects.