Ultrafast Dynamics Group
Frédéric Laquai's Group

Interplay Between Side Chain Pattern

Interplay Between Side Chain Pattern, Polymer Aggregation, and Charge Carrier Dynamics in PBDTTPD:PCBM Bulk-Heterojunction Solar Cells

Interplay Between Side Chain Pattern, Polymer Aggregation, and Charge Carrier Dynamics in PBDTTPD:PCBM Bulk-Heterojunction Solar Cells

Clare Dyer-Smith, Ian A. Howard, Clément Cabanetos, Abdulrahman El Labban, Pierre M. Beaujuge, and Frédéric Laquai
Advanced Energy Materials, Volume 5, Issue 9, (2015)
DOI 10.1002/aenm.201401778
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Clare Dyer-Smith, Ian A. Howard, Clément Cabanetos, Abdulrahman El Labban, Pierre M. Beaujuge, Frédéric Laquai
Charge Generation, PBDTTPD, Polymer Solar Cells, Structure–Property Relationships, Transient Absorption Spectroscopy
2015

PBDTTPD polymer donors with linear side-chains yield bulk-heterojunction (BHJ) solar cell power conversion efficiencies (PCEs) of about 4% with PC71BM as acceptor, while a PBDTTPD polymer with a combination of branched and linear substituents yields a doubling of the PCE to 8%. By using transient optical spectroscopy it is shown that while the exciton dissociation and ultrafast charge generation steps are not strongly affected by the side chain modifications, the polymer with branched side chains exhibits a decreased rate of nongeminate recombination and a lower fraction of sub-ns geminate recombination. In turn the yield of long-lived charge carriers increases, resulting in a 33% increase in short circuit current (Jsc). In parallel, the two polymers show distinct grazing incidence X-ray scattering spectra indicative of the presence of stacks with different orientation patterns in optimized thin-film BHJ devices. Independent of the packing pattern the spectroscopic data also reveals the existence of polymer aggregates in the pristine polymer films as well as in both blends which trap excitons and hinder their dissociation.