Solution Processed Cu₂CoSnS₄ Thin Films for Photovoltaic Applications

Earth abundant alternative chalcopyrite Cu₂CoSnS₄ (CCTS) thin films were deposited by a facile sol–gel process onto larger substrates. Temperature dependence of the process control of deposition and desired phase formations was studied in detail. Films were analyzed for complete transformation from amorphous to polycrystalline, with textured structures for stannite phase, as reflected from the X-ray diffraction and with nearly stoichiometric compositions of Cu:Co:Sn:S = 2:0:1:0:1:0:4:0 from EDAX analysis. Morphological investigations revealed that the CCTS films with larger grains, on the order of its thickness, were synthesized at higher temperature of 500 °C. The optimal band gap for application in photovoltaics was estimated to be 1.4 eV. Devices with SLG/CCTS/Al geometry were fabricated for real time demonstration of photoconductivity under A.M 1.5 G solar and 1064 nm infrared laser illuminations. A photodetector showed one order current amplification from ∼1.9 × 10^–6 A in the dark to 2.2 × 10^–5 A and 9.8 × 10^–6 A under A.M 1.5 G illumination and 50 mW cm^–2 IR laser, respectively. Detector sensitivity, responsivity, external quantum efficiency, and gain were estimated as 4.2, 0.12 A/W, 14.74% and 14.77%, respectively, at 50 mW cm^–2 laser illuminations. An <i>ON</i> and <i>OFF</i> ratio of 2.5 proved that CCTS can be considered as a potential absorber in low cost photovoltaics applications