Carrier Dynamics in Polymer Nanofiber:Fullerene Solar Cells

Abstract

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.

Effect of donor–acceptor molecular orientation on charge photogeneration in organic solar cells

“…7 and S5) were obtained from samples prepared using orientation-controlled singlelayer P3HT films (70 nm thick) and P3HT/PCBM bilayers (25 nm/30 nm, the same as the device fabrication conditions) prepared on quartz substrates. The spectral shape was consistent with several previous reports of TA signals in P3HT-PCBM systems 38,39,[48][49][50] . In the literature, the negative signals at approximately 550 ≤ λ ≤ 600 nm are well established to be attributable to photobleaching of the ground state of P3HT, indicating that excited species such as excitons and P3HT hole polarons were generated.…”

Recent progress in solar cells based on one-dimensional nanomaterials

“…The semiconducting polymers absorb light for charge generation and separation at the interface with electrode buffer layers. 163 To increase the charge transport and decrease charge localization, external electric field treatment of the active layer was conducted to align the randomly dispersed polymer chains to be perpendicular to the electrode. There are numerous reports focusing on the optimization of this bulk heterojunction layer containing polymer donor and acceptor to form a suitable micro-phase separation, which enhanced the carrier transport and favored high current density and fill factor.…”

Water‐Dispersed Conjugated Polyelectrolyte for Visible‐Light Hydrogen Production

“…Monitoring the transient dynamics of the GSB and PIA band would allow us to trace the evolution of these photoexcited species. As displayed in the right panel of Figure , even though photobleaching (PB) of both samples decay with almost the same trend at the earlier time, the sample containing Et 3 N exhibits longer tail dynamics ( τ 3 > 2 ns), which indicates the formation of long‐lived charges that scaped charge recombination as result of Et 3 N presence . Similar to PB signal, PIA of photogenerated charges probed at 700 nm also shows a long‐lived tail ( τ 3 > 2 ns) upon introduction of Et 3 N. The appearance of a long‐lived photoinduced absorption band beyond 600 nm indicates enhancement of free charge generation in photocatalytic system.…”