A new technique is proposed for the calculation of the width W of space charge region and consequently the concentration of uncompensated acceptors N-A-N-D, which is based on the open-circuit analysis of thin film heterojunction solar cells illuminated by monochromatic light with the wavelength within photosensitivity region. The proposed method was simulated under different values of the theoretically considered parameters (ideality coefficient n, saturation current I-0 and shunt resistance R-sh) of a CdS/CdTe heterojunction solar cell. The calculated values of W and N-A-N-D were established to be dependent on the mentioned above electrical parameters. (C) 2012 Elsevier Ltd. All rights reserved.