Understanding Processes Limiting Charge Collection in Organic Solar Cells

Organic solar cells have many advantageous properties including tailorable light absorption, low embodied energy manufacturing, structural conformality, and low material toxicity. However, owing to their low charge carrier mobilities, the competition between extraction and recombination of photogenerated charge carriers is an important factor limiting the performance of organic solar cells. This competition is further complicated by the inevitable presence of contact-induced dark carriers in the device. In this work, we clarify the effect of contact-induced dark charge carriers on photovoltaic device performance through theoretical device simulations. We find that first-order recombination between photogenerated carriers and contact-induced dark carriers is the dominant bimolecular recombination channel limiting charge collection in state-of-the-art organic solar cells. Furthermore, analytical models for the current-voltage characteristics are established. This work provides intriguing insights into the fundamental limits set by charge transport in organic photovoltaic devices.