Structure–property relationships of oligothiophene–isoindigo polymers for efficient bulk-heterojunction solar cells.

Zaifei Ma, Wenjun Sun, Scott Himmelberger, Koen Vandewal, Zheng Tang, Jonas Bergqvist, Alberto Salleo, Jens Andreasen, Olle Inganas, Mats R. Andersson, Christian Muller, Fengling Zhang, Ergang Wang

    Research output: Contribution to journalArticle

    91 Citations (Scopus)

    Abstract

    A series of alternating oligothiophene (nT)-isoindigo (I) copolymers (PnTI) were synthesized to investigate the influence of the oligothiophene block length on the photovoltaic (PV) properties of PnTI:PCBM bulk-heterojunction blends. Our study indicates that the number of thiophene rings (n) in the repeating unit alters both polymer crystallinity and polymer-fullerene interfacial energetics, which results in a decreasing open-circuit voltage (Voc) of the solar cells with increasing n. The short-circuit current density (Jsc) of P1TI:PCBM devices is limited by the absence of a significant driving force for electron transfer. Instead, blends based on P5TI and P6TI feature large polymer domains, which limit charge generation and thus Jsc. The best PV performance with a power conversion efficiency of up to 6.9% was achieved with devices based on P3TI, where a combination of a favorable morphology and an optimal interfacial energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work would be a valuable guideline for the design of high performance polymers with small energy losses during the charge generation process, allowing for the fabrication of efficient solar cells that combine a minimal loss in Voc with a high Jsc.

    Original languageEnglish
    Pages (from-to)361-369
    Number of pages9
    JournalEnergy & Environmental Science
    Volume7
    Issue number1
    DOIs
    Publication statusPublished - 2014

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  • Cite this

    Ma, Z., Sun, W., Himmelberger, S., Vandewal, K., Tang, Z., Bergqvist, J., Salleo, A., Andreasen, J., Inganas, O., Andersson, M. R., Muller, C., Zhang, F., & Wang, E. (2014). Structure–property relationships of oligothiophene–isoindigo polymers for efficient bulk-heterojunction solar cells. Energy & Environmental Science, 7(1), 361-369. https://doi.org/10.1039/c3ee42989j