Recombination and charge transfer states in organic photovoltaics: from small molecules to ultra-low band gap polymers (Conference Presentation)

• DOI: 10.1117/12.2319926
• Publication Date: 2018-09-17T16:18:21Z
• Authors: Tracey M. Clarke; Kealan Fallon; Michelle Vezie; Enrico Salvadori; Jordan Shaikh; Christopher Kay; Artem Bakulin; Jenny Nelson; Hugo Bronstein
• Keywords: Intersystem crossing; HOMO/LUMO

Diketopyrrolopyrrole (DPP) is one of the most common building blocks for small molecules and conjugated polymers designed organic electronic applications. Transient absorption spectroscopy (TAS) time-resolved electron paramagnetic resonance (TR-EPR) were used to examine bulk heterojunction blend films a diketopyrrolopyrrole-based molecule, TDPP, with fullerene derivatives PC60BM PC70BM. Following pulsed laser excitation, spectral signatures anion TDPP triplet state are observed on picosecond timescale by TAS. The presence these species imply formation TDPP:PCBM charge transfer that subsequently undergoes ultra-fast spin-mixing geminate recombination produce state. overall photophysical mechanism confirmed TR-EPR spectroscopy, which unambiguously shows formed via in state, rather than direct intersystem crossing from excited singlet Furthermore, ultra-low band gap INDT investigated further using transient pump-push photocurrent measurements. Different fullerenes trialled assess effect photogeneration. LUMO levels donor acceptor almost isoenergetic (implying virtually zero driving force separation) this reflected inefficient A ketolactam deeper produces higher level Interestingly, it was discovered may possibly generate an intramolecular CT state-like exciton, only able be efficiently separated deep enough LUMO.