Photovoltaic properties and femtosecond time‐resolved fluorescence study of polyoxometalate‐containing rod–coil diblock copolymers

The photovoltaic properties and exciton decay dynamics of three polyoxometalate (POM)-containing hybrid rod–coil diblock copolymers (HDCPs), PS-Mo6-PT1–3, are studied. Single-component photovoltaic cells of PS-Mo6-PT2 and inverted solar cells based on ZnO nanorod arrays/PS-Mo6-PT1–3 are fabricated showing power conversion efficiencies only up to 0.055%. To understand the poor photovoltaic performance, femtosecond fluorescence up-conversion technique is used to study the exciton decay dynamics of all three HDCPs. Drastically different fluorescence dynamics of the three HDCPs are observed in dilute solutions, which is attributed to the different extent and different type of interpolymer association depending on the P3HT rod block length and the cluster loading ratio. While both cation-mediated POM cluster association and P3HT-P3HT π-stacking contribute significantly to PS-Mo6-PT2 aggregation, the aggregation of PS-Mo6-PT1 and that of PS-Mo6-PT3 is driven predominantly by cluster association and π-stacking, respectively. In conjunction with the high residual polarization anisotropy, it is concluded that charge transfer from P3HT excitons to POM clusters in all three HDCPs is inefficient. An improved system with direct π-conjugation between the POM clusters and the rod block addressing this issue has been proposed. © 2013 Wiley Periodicals, 2014, 52, 122–133