Investigation of electric charge transport in conjugated polymer P3HT: PCBM solar cell with temperature dependent current and capacitance measurements

We investigated quantitatively the electronic transport properties of a bulk heterojunction polymer/fullerene solar cell, based on structure Glass/ITO/P3HT:PCBM/Al. The current-voltage I-V characteristics in the intermediate positive bias and temperature regime (0.2 V <= V <= 1.5 V, 180 K <= T <= 250 K) can be well fitted by a modified Poole-Frenkel PF detrapping model. Combining these results with the high frequency capacitance measurements, we could then derive independently the absorber thickness and its dielectric constant. At low temperature (80 K <= T <= 170 K), the I-V data can be well accounted for with Space Charge Limited Current (SCLC) regimes. At intermediate positive bias (1V <= V <= 2.3V), the current is dominated by the trapped space charges with an exponential traps distribution, while at high positive bias (2.5 V <= V <= 4 V), the space charges due to injected free carrier play an important role for the conduction. From the fits to the two different SCLC models, we could then extract the electrically active defects parameters controlling the transport. These parameters were confirmed by space charge capacitance spectroscopy. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim