Novel, Facile Back Surface Treatment for CdTe Solar Cells

Formation of a Te-rich surface on the CdTe absorber is beneficial to the formation of a low barrier contact at the back junction in CdTe solar cells. Regardless of the CdTe fabrication method, surface etching processes are widely used to form Te-rich surfaces. Here, we show that methylammonium iodide (CH
₃
NH
₃
I, MA!) can simply and controllably react with the CdTe surface to produce elemental tellurium. Both X-ray diffraction and Raman spectroscopy confirmed formation of a Te layer. Devices constructed with the MAI-treated CdTe absorber exhibited higher photovoltaic parameters of open circuit voltage (V
_oc
) and fill factor (FF) relative to similar devices prepared without the MA! treatment. This indicates a reduction in the Schottky barrier at the back contact due to the MAI surface treatment. CdTe samples that were treated with 125 mM MAI solution and heated to 150 °C for 10 minutes showed the best power conversion efficiency (PCE) of 13.5% while without treating the standard device efficiency was 12.7%.