We report on the observation of a charge-transfer state forming at the molecular interface between a conjugated polymer and a fullerene based electron acceptor. Electron hole recombination in this state results in a luminescent transition at 840nm, energetically separated from the polymer emission. This transition can be directly photoexcited by tuning the excitation energy below the conjugated polymer bandgap, demonstrating that the charge-transfer state originates from a ground-state interaction. By electric field induced quenching of the photoluminescence, we determine a binding energy of 130meV for excitons in the charge-transfer state.
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.
We correlate carrier recombination via charge transfer excitons (CTEs) with the short circuit current, Jsc, in polymer/fullerene solar cells. Near infrared photoluminescence spectroscopy of CTE in three blends differing for the fullerene acceptor, gives unique insights into solar cell characteristics. The energetic position of the CTE is directly correlated with the open-circuit voltage, Voc, and more important Jsc decreases with increasing CTE emission intensity. CTE emission intensity is discussed from the perspective of blend morphology. The work points out the fundamental role of CTE recombination and how optical spectroscopy can be used to derive information on solar cell performances.
Among the different recombination mechanisms in organic solar cells the
photoluminescence (PL) of charge transfer excitons (CTEs) has been
identified has one of the most important, impacting both the open circuit
voltage and the short circuit current. Here, we study their recombination
dynamics, monitoring the decay of the PL on a time scale spanning three
orders of magnitude from nanoseconds to microseconds. As a model system we
investigate blends of the conjugated polymer
poly(2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylene-vinylene) (MDMO-PPV)
and the fullerene derivative [6,6]-phenyl C61-butyric acid methyl
ester (PCBM). We observe that the dynamics of recombination follows a
power-law, which is independent of sample morphology. Upon application of a
transient electric field, which is capable of separating the bound charge
pairs, we observe different dynamics of recombination only for the separated
pairs. Those also follow a power-law and show a strong dependence on the
film morphology.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.