The evolution of charge carriers mobility mu and their concentration p in the diode devices with the architecture: indium tin oxide (ITO)/poly(3-hexylthiophene) (P3HT)/Al, subjected to photothermal aging in argon atmosphere was investigated using Current Extracted by the non-Linearly Increasing Voltage (CEnLIV) technique based on measuring charge carrier extraction under applied voltage pulses of arbitrary shape and limited amplitude. The kinetics of accumulation of radicals in the P3HT films was explored by the electron spin resonance (ESR) spectroscopy under similar conditions. A remarkable dynamics of mu and p in the system was observed after applying bias voltage to the photothermally aged P3HT-based diode devices. This process was shown to be fully reversible and the system undergoes relaxation to the original state after removal of the bias voltage. The experimental data reflecting the photothermal degradation of P3HT in the presence of trace amounts of oxygen trapped in the films were explained by the proposed kinetic scheme describing the interactions of free charge carriers with the donor-acceptor pairs. (C) 2016 Elsevier B.V. All rights reserved.