Selenization of copper indium gallium disulfide nanocrystal films for thin film solar cells

Recently, numerous non-vacuum methods have been demonstrated for the fabrication of Cu(In_xGa_1-x)Se₂ (CIGSe) thin films and solar cells via selenization of various precursor materials. However, composition control and uniformity at all scales remains a challenge. Here we present a promising alternative approach using Cu(In_1-xGa_x)S₂ (CIGS) nanocrystal inks for low cost fabrication of CIGSSe absorber films. By using nanocrystal inks of CIGS as the precursor for selenization, the composition can be controlled at all scales. Nanocrystals with varying Ga concentration can also be used to form graded band gap CIGSSe absorber film. Initial devices fabricated using a graded CIGSSe absorber layer showed a photon to electricity conversion efficiency of 6.23% corresponding to an active area efficiency of 7.10% under AM1.5 illumination.