Organic photovoltaic (OPV) devices fabricated with P3HT nanofiber (NF) networks typically exhibit poorer device performance compared to their nanoscale phase separated P3HT:PCBM counterparts despite possessing superior light harvesting properties and high in-plane charge mobility. Herein, we investigate the charge generation and recombination dynamics in P3HT-NF:PCBM blend films using transient absorption spectroscopy (TAS) spanning a wide temporal range over 7 orders of magnitude (i.e., from 100 fs to 1 μs), which are correlated with device performance studies. TAS reveals a more efficient charge generation and polaron formation rate in the NF samples as compared to the control samples at the onset which persists up to ∼2 ns. However, within the nanoseconds to microseconds time scale, there is a significant amount of nongeminate recombination in the NF system. We attribute this to the poor interfibrillar charge transport between the NFs, which tend to align parallel to the electrodes, thereby causing charge localization. These charge dynamics were validated using the analytical model proposed by Laquai and co-workers et al. J. Am. Chem. Soc. 2010, 132, 14866]. Importantly, our findings provide new insights into the factors that limit the photovoltaic performance of such P3HT-NF based devices.

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Recent work on hybrid photovoltaic systems based on conjugated polymers and III-V compound semiconductors with relatively high power conversion efficiency revived fundamental questions regarding the nature of charge separation and transfer at the interface between organic and inorganic semiconductors with different degrees of delocalization. In this work, we studied photoinduced charge generation and interfacial transfer dynamics in a prototypical photovoltaic n-type GaAs (111)B and poly(3-hexyl-thiophene) (P3HT) bilayer system. Ultrafast spectroscopy and density functional theory calculations indicate the coexistence of electron and hole transfer at the GaAs/P3HT interface, leading to the generation of long-lived species and photoinduced absorption upon creation of hybrid interfacial states. This opens up new avenues for the use of low-dimensional III-V compounds (e.g., nanowires or quantum dots) in hybrid organic/inorganic photovoltaics, where advanced bandgap and density of states engineering may also be exploited as design parameters.

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