Enhanced Photogeneration of Triplet Excitons in an Oligothiophene–Fullerene Blend

Abstract

Photoinduced and transient absorption spectroscopy is used to study triplet exciton dynamics in thin films of a new thiophene-based oligomer (DCV3T) and blends of DCV3T and fullerene C60. We find enhanced DCV3T triplet exciton generation in the blend layer, which is explained as an excitonic ping-pong effect: singlet energy transfer from DCV3T to C60, followed by immediate intersystem crossing to C60, and triplet exciton back-transfer. Estimations of the rate constants involved show that the ping-pong effect has an overall efficiency close to unity. The singlet-singlet energy transfer from DCV3T to C60 is demonstrated by efficient quenching of DCV3T luminescence in the blend, leading to sensitized emission of C60. We discuss a promising new concept of solar cells with an enlarged active-layer thickness based on potentially long-ranged triplet exciton diffusion in combination with efficient intersystem crossing.

Selective Triplet‐State Formation during Charge Recombination in a Fullerene/Bodipy Molecular Dyad (Bodipy=Borondipyrromethene)

“…A similar strategy has been proposed for increasing the triplet yield in oligophenylene-C 60 blends and termed the "ping-pong" mechanism. [49] For Bodipy-C 60 , the equilibrated mixture of triplet states is dominated by the C 60 triplet. Thus, from the energy gap, the percentage Bodipy triplet in the mixture is calculated to be 15 % at 25 8C, whereas spectral records indicate that the mixture contains % 25 % of the Bodipy triplet.…”

Organic Thin‐Film Photovoltaic Cells Based on Oligothiophenes with Reduced Bandgap

“…The second type of solar cells comprises a blend layer of DCV3T and C 60 . The admixture of C 60 to DCV3T leads to an enhanced generation of triplet excitons on DCV3T, [9] which can diffuse to the interface of a donor-type layer, where they are separated into pairs of free charge carriers. Because of their long lifetime, these triplet excitons have the potential to reach long diffusion lengths and thus to increase the thickness of the photoactive layer.…”

“…9) indicate that singlet excitons on the DCV3T are transferred to a singletexciton-state on the C 60 . [9] On the C 60 molecules, the singlet excitons undergo inter-system-crossing (ISC) to the triplet state, which is known to be very efficient in C 60 . [23] Finally, triplet-excitons are transferred back to the DCV3T as we could show by photoinduced absorption spectroscopy (PIA) at low temperatures (T = 10 K): [9] The PIA spectra (Fig.…”

“…[9] On the C 60 molecules, the singlet excitons undergo inter-system-crossing (ISC) to the triplet state, which is known to be very efficient in C 60 . [23] Finally, triplet-excitons are transferred back to the DCV3T as we could show by photoinduced absorption spectroscopy (PIA) at low temperatures (T = 10 K): [9] The PIA spectra (Fig. 10) of both neat DCV3T layers and blend layers with C 60 show the same feature at 1.5 eV attributed to a triplet-triplet (T 1 → > T n ) transition of DCV3T.…”

Ferrocenyl‐Ended Thieno–Vinylene Oligomers: Donor–Acceptor Polarization and Mixed‐Valence Properties with Emphasis on the Raman Mapping of Localized‐to‐Delocalized Transitions

“…One of the most useful organic molecules in (opto)-electronics is the family of oligothiophenes which have been implemented in devices such as field effect transistors (FETs), [1] light emitting diodes (LEDs), lasers, [2] and photovoltaic cells. [3] Very advantageous in this field is the possibility of the tuning of the molecular architecture pursuing optimal electronic response and, consequently, oligomers of thiophene have been co-oligomerized or combined in the same conjugational path with other conjugating groups such as acetylene, benzene, pyrrol and vinylene. [4] Another strategy is the substitution of the terminal a-positions with electro-active groups trying to facilitate electronic communication and charge polarization.…”