Gregory M. Su

Recent progress in the morphology of bulk heterojunction photovoltaics

A review of current research in the characterization of the morphology of semiconducting polymer:fullerene bulk heterojunctions (BHJs) is presented. BHJs are complex blends of polymers and fullerenes with nanostructures that are highly dependent on materials, processing conditions, and post-treatments to films. Recent work on the study of the morphology of BHJs is surveyed. Emphasis is placed on emerging work on BHJs of poly(3-hexylthiophene), P3HT, and [6,6]-phenyl-C61-butyric acid methyl ester, PCBM, along with BHJs of donor–acceptor polymers that have high power conversion efficiency.

Linking morphology and performance of organic solar cells based on decacyclene triimide acceptors

Bulk heterojunction photovoltaic devices consisting of a novel non-fullerene acceptor based on a decacyclene triimide core and the common polymer donor poly(3-hexylthiophene) exhibit good power conversion efficiency (∼1.6%) as-cast. However, thermal annealing results in a drastic decrease in both the efficiency and the electron current. Polarized soft X-ray spectroscopy and grazing incidence X-ray scattering reveal that thermal annealing results in a reorientation of the acceptor molecules to an edge-on orientation with their π–π stacking direction predominantly in-plane with the substrate and overall hexagonal packing among planar columnar structures. This packing motif greatly hinders vertical electron transport in bulk heterojunction films. Furthermore, in situ X-ray scattering studies show that this critical reorientation occurs even at relatively low temperatures (∼60 °C). These results are some of the first to highlight differences between the morphology of non-fullerene and fullerene-based bulk heterojunctions and critical parameters that must be controlled when designing future high-performance non-fullerene acceptor molecules.