Large cubic tin sulfide–tin selenide thin film stacks for energy conversion

• Large cubic tin sulfide and tin selenide thin films are stacked via chemical deposition.
• When heated, the stacks produce solid solutions of SnS-Se-CUB.
• Such stacks have optical band gap 1.5 eV and electrical conductivity 0.01 Ω− 1 cm− 1.
• They are promising materials for solar cells and thermoelectric conversion.

Large cubic (CUB) polymorphs of SnS and SnSe were identified in nanocrystals and in thin films during 2015–16. We present how thin films of SnS-CUB and SnSe-CUB can be stacked in different sequences to thickness of 450 nm by chemical deposition. Grazing incidence X-ray diffraction pattern of the films establishes how these stacks of materials with a lattice constant a = 11.59 Å for SnS-CUB and 11.96 Å for SnSe form, upon heating at 300 °C, composite layers of SnS-CUB + SnS0.75Se0.25-CUB + SnSe-CUB. The layers so formed have optical band gap of nearly 1.52 eV, intermediate to that of SnSe-CUB and SnS-CUB, of 1.38 and 1.73 eV, respectively. With optical absorption coefficient exceeding 105 cm− 1 in the visible region, the stacks would produce light generated current density of 28–31 mA/cm2 in solar cells for air mass 1.5 global solar radiation. Electrical conductivity of 0.01 Ω− 1 cm− 1, and Seebeck coefficient of up to 0.48 mV/K of the layers suggest their possible application in thermoelectric converters as well.