Boron doped CdS films were prepared by chemical bath deposition, which is a low-cost and large-area technique and appears to be well-suited for the manufacture of thin film solar cells, using boric acid (H3BO3) as dopant source, and their properties were investigated as a function of doping concentration. In addition, effects of the boron doping of the CdS films on the characteristics of CdS/CdTe solar cells were investigated. As the boron doping concentration increased, the resistivity of CdS films rapidly decreased and exhibited the lowest resistivity of 2 Omega cm at 0.01 of H3BO3/CdAc2 mole ratio. Boron doping into CdS films improved the optical transmittance in the visible region of light and increased the optical band gap. The photovoltaic characteristics of CdS/CdTe solar cells using boron doped US film as the window layer were improved due to the increase of the electrical conductivity and the optical band gap of CdS films. (C) 2003 Elsevier Science B.V. All rights reserved.