Charge Transfer Excitons in Polymer/Fullerene Blends: The Role of Morphology and Polymer Chain Conformation

Here, it is shown how carrier recombination through charge transfer excitons between conjugated polymers and fullerene molecules is mainly controlled by the intrachain conformation of the polymer, and to a limited extent by the mesoscopic morphology of the blend. This experimental result is obtained by combining near‐infrared photoluminescence spectroscopy and transmission electron microscopy, which are sensitive to charge transfer exciton emission and morphology, respectively. The photoluminescence intensity of the charge transfer exciton is correlated to the degree of intrachain order of the polymer, highlighting an important aspect for understanding and limiting carrier recombination in organic photovoltaics. Charge transfer excitons are one significant recombination channel in polymer/fullerene bulk heterojunction solar cells. Here, a weak dependence of their photoluminescence intensity on morphology is observed, whereas the chain conformation of the polymer plays a crucial role. Conjugated polymers such as RE‐P3HT, with a high degree of intrachain order, show a weak charge transfer emission when compared to MDMO‐PPV and ra‐P3HT. The results highlight an important strategy in limiting the recombination via charge transfer excitons.