Charge carrier recombination in organic solar cells

Solution deposited bulk heterojunction organic solar cells are viewed as one of the most promising alternative energy sources because of their ease of processing and their potential to be produced using large scale techniques such as roll-to-roll, newspaper style, coating. Since organic materials have a relatively low dielectric constant the dissociation of an excited electron–hole pair into free collectable charge carriers is inefficient in many cases. Often the excited electron–hole pairs recombine back to the ground state in a process known as geminate recombination before they ever fully dissociate into free charge carriers. Even after dissociation, free holes and electrons can encounter each other once more and subsequently recombine back to the ground state in a process known as nongeminate recombination. In both cases the incident photon energy is lost and fewer carriers are collected at the electrodes. Hence, charge carrier recombination is one of the key loss mechanisms in organic solar cells. In this review the latest on geminate and nongeminate recombination is discussed.