Structure-Property Relationships of Oligothiophene-Isoindigo Polymers for Efficient Bulk-Heterojunction Solar Cells
2014 (English)In: energy and environmental science, ISSN 1754-5692, Vol. 17, no 1, 361-369 p.Article in journal (Refereed) Published
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 favorable morphology and optimal interface energy level offset ensures efficient exciton separation and charge generation. The structure-property relationship demonstrated in this work is 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.
Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014. Vol. 17, no 1, 361-369 p.
organic solar cell, fullerene, conjugated polymer, charge transfer state
Natural Sciences Engineering and Technology
IdentifiersURN: urn:nbn:se:liu:diva-99424DOI: 10.1039/c3ee42989jISI: 000329550700025OAI: oai:DiVA.org:liu-99424DiVA: diva2:656978