Analysis of voltage and temperature dependent photocurrent collection in p3ht/pcbm solar cells

Current-voltage (J-V) analysis of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) blend organic solar cells (OSC) at various temperatures has been recorded and analyzed. The photovoltaic parameters extracted from a lumped circuit analysis completely describe the illuminated J-V data from far reverse bias to beyond the open circuit voltage (V-oc). A simple model for carrier collection, previously applied to inorganic thin film solar cells, has been used to describe the voltage dependence of the photocurrent, J(L)(V), with only one adjustable parameter, L-c/D, the ratio of the carrier collection length to the active-layer thickness. Measured J-V curves of a variety of OSCs with varying thickness and blend ratios are closely fit with this model. Effect of resistive and collection losses has been quantified and removed, allowing the intrinsic junction behavior to be uncovered. The temperature dependence of V-oc is linear with negative temperature coefficient, dV(oc)/dT, similar to -1 mV/K. The values of the effective bandgap of the blend obtained from the intercept at T = 0 K decrease with the increase of the PCBM concentration. Our data support the idea of existence of mid-bandgap states, which increase with the increase in the disorder in the active layer. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4768910]