Key factors behind the superior performance of polymer-based NFA blends

All-small molecule (ASMs) solar cells have great potential to actualize the commercialization of organic photovoltaics owing to their higher solubility, lesser batch-to-batch variety and simpler synthesis routes compared to the blend systems that utilize conjugated polymers. However, the efficiencie...

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Bibliographic Details
Published in:Materials horizons 2024-10, Vol.11 (21), p.534-5312
Main Authors: Sa lamkaya, Elifnaz, Shadabroo, Mohammad Saeed, Tokmoldin, Nurlan, Melody, Tanner M, Sun, Bowen, Alqahtani, Obaid, Patterson, Acacia, Collins, Brian A, Neher, Dieter, Shoaee, Safa
Format: Article
Language:English
Subjects:
Carrier mobility
Charge transfer
Chemical synthesis
Commercialization
Current carriers
Electron transport
Excitons
Heterojunctions
Photovoltaic cells
Polymer blends
Polymers
Solar cells
Space charge
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Summary:All-small molecule (ASMs) solar cells have great potential to actualize the commercialization of organic photovoltaics owing to their higher solubility, lesser batch-to-batch variety and simpler synthesis routes compared to the blend systems that utilize conjugated polymers. However, the efficiencies of the ASMs are slightly lacking behind the polymer: small molecule bulk-heterojunctions. To address this discrepancy, we compare an ASM blend ZR1:Y6 with a polymer:small molecule blend PM7:Y6, sharing the same non-fullerene acceptor (NFA). Our analyses reveal similar energetic offset between the exciton singlet state and charge transfer state (Δ E S 1 -CT ) in ZR1:Y6 and PM7:Y6. In comparison to the latter, surprisingly, the ZR1:Y6 has noticeably a stronger field-dependency of charge generation. Low charge carrier mobilities of ZR1:Y6 measured, using space charge limited current measurements, entail a viable explanation for suppressed charge dissociation. Less crystalline and more intermixed domains as observed in the ZR1:Y6 system compared to polymer:Y6 blends, makes it difficult for NFA to form a continuous pathway for electron transport, which reduces the charge carrier mobility. Suppressed face-on stacking and crystallinity in ZR1:Y6 reduce charge dissociation, leading to more field-dependent charge generation compared to PM7:Y6, despite similar energy offsets in both blends.
ISSN:2051-6347
2051-6355
2051-6355
DOI:10.1039/d4mh00747f