Effect of energetic disorder on the open-circuit voltage in organic bulk heterojunction composites

Abstract

Under open-circuit condition, the current is not extracted and the photogenerated carriers in principle disappear only by recombination. We study the open-circuit voltage and transient photovoltage under the effect of bulk recombination in a medium with energetic disorder by using the multiple trapping (MT) model. The key parameter in the MT model is the dispersion parameter given by the ratio of thermal energy to the characteristic energy of trap states. We show that depends linearly on the logarithm of the light intensity and the slope depends on the of the MT model. Under the continuous irradiation of light, the photovoltage response to the weak perturbation by a pulsed light obeys pseudo-first-order decay. The rate as a function of is independent of the dispersion parameter. However, it obeys the power law as a function of light intensity, and the exponent is given by , which reduces to 1/2 in the absence of energetic disorder.