In this contribution we present an in situ method for the preparation of CuInS2-poly(3-(ethyl-4-butanoate)thiophene)(P3EBT)nanocomposite layers and their application in nanocomposite solar cells. A precursor solution containing copper and indium salts, thiourea and the conjugated polymer was prepared in pyridine, which was coated onto glass/ITO substrates followed by a heating step at 180 degrees C. The heating step induced the formation of the CuInS2 nanoparticles homogeneously dispersed in the conjugated polymer matrix. The formation of the nanocomposite was investigated in situ by X-ray scattering techniques and TEM methods showing that nano-scaled CuInS2 was formed. By addition of small amounts of zinc salt to the precursor solution, zinc containing CuInS2 (ZCIS) was formed. ZCIS-P3EBT active layers exhibited higher V-OC than CuInS2-P3EBT layers and showed efficiencies of about 0.4%. Additionally the stability of the solar cells was tested over a time scale of 172 h. (C) 2010 Elsevier B.V. All rights reserved.