CZTS solar cells on graphite without Mo-coated glass substrate

Abstract

The use of graphite substrates has been demonstrated in thin-film Cu2ZnSnS4 (CZTS) solar cells and can serve as alternative electrodes for next-generation, thin-film solar cells. From the early stages of CZTS development, Mo-coated substrates composed of copper (Cu), zinc (Zn), tin (Sn), and sulfur (S) have been employed for stability at high temperature. However, Mo has become a rare metal in recent years; correspondingly, there are potential risk of supply shortages and depletion problems. We focus herein on graphite as an electrode and substrate owing to its versatility and low cost. The CZTS precursor was prepared by radiofrequency sputtering. Subsequently, NaF was deposited using the E-B vapor deposition method to control the Na composition ratio. CZTS films were obtained by gas-phase sulfurization at 898 K for 1 h. CZTS solar cells with MgF2/Al/AZO/CdS/CZTS/graphite structure were prepared, and their characteristics were evaluated. J–V measurement of the precursor with a 20 nm thick NaF yielded η = 2.37%, V oc = 543 mV, J sc = 10.7 mA cm−2, and FF = 40.8%. These results suggest that CZTS on graphite with NaF control has the potential for realizing the low cost CZTS solar cells.