5739wileyonlinelibrary.com deposition method, which is facile, benign, and which can deposit a uniform MS thin fi lms is highly desirable. Although various available techniques such as chemical vapor deposition, [ 9,10 ] atomic layer deposition, [ 11,12 ] molecular beam epitaxy, [ 13,14 ] electrodeposition, [ 7,15 ] successive ionic layer adsorption and reaction, [ 16,17 ] vapor sublimation, [ 18 ] etc., are able to produce thin fi lms of MS, they lack generality or need sophisticated instrumentation, and are complicated. In this context, chemical bath deposition is inarguably the simplest method for thin fi lm deposition. Generally, a suitable complexing agent and pH regulating agents are added in order to avoid spontaneous precipitation in an aqueous bath, which makes the process complicated due to extremely critical optimization for concentration of complexing agents and pH adjustment for an individual MS case. [ 4,[19][20][21][22] As a result, development of MS fi lms by solution-based method has often been a case of trial-and-error with poor reproducibility, which remained as an unexplored research fi eld yet in material science and technology. In order to tackle the above problems in aqueous solution, the fi lm deposition reaction is carried out in ethanol solution without the use of any complexing and/or pH-regulating agents. This protocol relies on dissolution of metal salts and thioacetamide in ethanol and heating the solutions at 70 °C. Although very few reports on MS fi lm deposition from nonaqueous solution has been reported, [ 23,24 ] no general protocol is available that can be applied overall to deposit all variety of MS thin fi lms under similar conditions with good reproducibility. The proposed protocol is extremely simple and general, which can lay simple guidelines to fabricate almost all types of metal sulfi des uniformly over all area of the substrate, provided that the corresponding metal salts are soluble in ethanol. The as-deposited MS fi lms are highly crystalline even without thermal treatment. Interestingly, the fi lms can be directly grown on variety of conducting as well as non-conducting substrates such as glass, plastic, fl uorine doped tin oxide (FTO), Ti-foil, carbon paper, Whatman fi lter paper, etc., which can be of great technological importance. As an example of potential application of these thin fi lms, we demonstrate the use of NiS fi lm deposited on fl exible plastic substrates as FTO-free dual-functioned (electronic support + electrocatalytic) counter electrode in dye-sensitized solar cells
Revisiting Metal Sulfi de