Intercalated vs Nonintercalated Morphologies in Donor-Acceptor Bulk Heterojunction Solar Cells: PBTTT:Fullerene Charge Generation and Recombination Revisited
- In this Letter, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and nonintercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the nonintercalated system and almost vanishes when energetic disorder is included in the model. Despite these differences, both femtosecond-resolved transient absorption spectroscopy (TAS) and time-delayed collection field (TDCF) exhibit extensive first-order losses in both systems, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene-aggregated domains (1:4 PBTTT:PC70BM) is the only one that shows slow,In this Letter, we study the role of the donor:acceptor interface nanostructure upon charge separation and recombination in organic photovoltaic devices and blend films, using mixtures of PBTTT and two different fullerene derivatives (PC70BM and ICTA) as models for intercalated and nonintercalated morphologies, respectively. Thermodynamic simulations show that while the completely intercalated system exhibits a large free-energy barrier for charge separation, this barrier is significantly lower in the nonintercalated system and almost vanishes when energetic disorder is included in the model. Despite these differences, both femtosecond-resolved transient absorption spectroscopy (TAS) and time-delayed collection field (TDCF) exhibit extensive first-order losses in both systems, suggesting that geminate pairs are the primary product of photoexcitation. In contrast, the system that comprises a combination of fully intercalated polymer:fullerene areas and fullerene-aggregated domains (1:4 PBTTT:PC70BM) is the only one that shows slow, second-order recombination of free charges, resulting in devices with an overall higher short-circuit current and fill factor. This study therefore provides a novel consideration of the role of the interfacial nanostructure and the nature of bound charges and their impact upon charge generation and recombination.…
| Author details: | Elisa Collado-Fregoso, Samantha N. Hood, Safa Shoaee, Bob C. Schröder, Iain McCulloch, Ivan Kassal, Dieter NeherORCiDGND, James R. Durrant |
|---|---|
| DOI: | https://doi.org/10.1021/acs.jpclett.7b01571 |
| ISSN: | 1948-7185 |
| Pubmed ID: | https://pubmed.ncbi.nlm.nih.gov/28777583 |
| Title of parent work (English): | The journal of physical chemistry letters |
| Publisher: | American Chemical Society |
| Place of publishing: | Washington |
| Publication type: | Article |
| Language: | English |
| Year of first publication: | 2017 |
| Publication year: | 2017 |
| Release date: | 2020/04/20 |
| Volume: | 8 |
| Number of pages: | 8 |
| First page: | 4061 |
| Last Page: | 4068 |
| Funding institution: | UNVEIL; BMBF project; EPSRC [EP/IO1927B/1, EP/M023532/1, EP/K011987/1]; Welsh Assembly Government Ser Cymru programme; CONACyT [309929]; Kernahan Fund from Imperial College London; Westpac Bicentennial Foundation; Australian Research Council through a Discovery Early Career Researcher Award [DE140100433]; Australian Research Council through Centre of Excellence for Engineered Quantum Systems [CE110001013] |
| Organizational units: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie |
| Peer review: | Referiert |
