PROBLEM TO BE SOLVED: To provide an aqueous solution composition capable of forming metal sulfide with few impurities by a solution deposition method; a metal sulfide thin film formed by using the aqueous solution composition; a photoelectric conversion element using the thin film as a buffer layer; and metal sulfide particles.SOLUTION: The aqueous solution composition includes a thiourea derivative, represented by R, R-N-C(=S)-N-R, Rwhere at least one of Rto Ris other than an H atom and at least one contains an N atom, and a metal ion which forms a poorly soluble sulfide. Also provided are a metal sulfide film and powder in an IR spectrum of which, when a maximum intensity in 2000 to 2100 cmis denoted by IR-1, a maximum intensity in 1000 to 1200 cmby IR-2, and a maximum intensity in 1500 to 1700 cmby IR-3, both IR-1/IR-2 and IR-1/IR-3 are less than 0.5.
