Large cubic tin sulfide-tin selenide thin film stacks for energy 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 angstrom for SnS-CUB and 11.96 angstrom for SnSe form, upon heating at 300 degrees 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/cm(2) in solar cells for air mass 1.5 global solar radiation. Electrical conductivity of 0.01 Omega(-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. (C) 2016 Elsevier B.V. All rights reserved.