Controllable indium doping for high efficiency CZTS thin-film solar cells

A method for forming a photovoltaic device, comprising:

• providing an absorber layer initially devoid of indium (In) and including Cu—Zn—Sn—S(Se) (CZTSSe) on a first contact layer formed on a substrate;
• forming a buffer layer initially devoid of In and having a first surface and a second surface, the first and second surfaces in opposed relation to each other, such that the first surface is in contact with the absorber layer;
• diffusing In from an ultrathin In layer into the buffer layer such that a portion of the ultrathin In layer remains on the surface of the buffer layer, the ultrathin In layer having a valence value between dominant valence values of the absorber layer and the buffer layer;
• and
• forming a transparent conductive contact layer over the portion of the ultrathin In layer remaining on the buffer layer after In diffusion.