SPLTRAK Abstract Submission
Optical Characterization of Thin Film CuxAlOy in the CdTe Device Configuration 
Indra Subedi, Kamala Khanal Subedi, Prabin Dulal, Adam B Phillips, Michael J Heben, Randy J Ellingson, Nikolas J Podraza
Department of Physics & Astronomy and Wright Center for Photovoltaics Innovation & Commercialization, The University of Toledo, Toledo, OH, United States

Cadmium telluride (CdTe) based thin film solar cells are the most commercially produced photovoltaic (PV) devices after wafer-based crystalline silicon cells. Most of the well-known and widely used transparent conducting oxides (TCO) thin film materials commonly used in PV devices such as aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO), and tin doped indium oxide (ITO) are n-type materials with only a few existing materials showing p-type conductivity and visible spectral range transparency. Solution processed thin film copper aluminum oxide (CuxAlOy) has p-type conductivity and can be used as the transparent back contact and passivation layer for both mono-facial and bifacial CdTe based thin film solar cells. Thin film CuxAlOy layer is deposited by low cost, non-vacuum, and solution processed spin coating method. We use spectroscopic ellipsometry from the near infrared to ultraviolet range to evaluate the complex optical properties of thin film CuxAlOy deposited on sodalime glass as well as structural parameters in the CdTe solar cell device stack.  For thin film CuxAlOy , the direct optical bandgap obtained to be 3.64 ± 0.01 eV. Further characterization is also done with this layer on CdTe / CdS / highly resistive transparent (HRT) layer / TCO device stack. CuxAlOy conformally coats CdTe in the CdTe / CdS / HRT layer / TCO device stack indicating improved surface passivation and potential reduction in electronic losses at the rear contact.