Abstract
We review recent progress in the development of organic bulk heterojunction (BHJ) solar cells employing donor–acceptor copolymers as the electron-donor and fullerene derivatives as the electron-acceptor. We discuss the role of the donor and acceptor moieties, side-chains, bridging units and atomic substitutions of the copolymers on their optoelectronic functionality. The physical properties, e.g. molecular conformation, miscibility, phase-separated lateral and vertical morphology, of various photovoltaic blends prepared via solution casting and post-treatments are reviewed and correlated with photovoltaic device performance. Factors influencing the morphological stability of polymer:fullerene BHJ thin-films are briefly discussed. Finally, we address the use of thin organic interlayers to increase the efficiency of BHJ solar cells.
Highlights
Bulk heterojunction (BHJ) organic photovoltaic (OPV) devices employing conjugated polymers as electron donors and fullerene derivatives as electron acceptors convert the energy of sunlight into electrical current using the photovoltaic effect.[1,2]
It was found that shorter side chains gave rise to a BHJ morphology, containing fullerene aggregates described by the authors as being ‘pea-like’, whereas blends of a fullerene and polymer having longer side chains formed a relatively coarse interpenetrating network characterized by larger phase separation between the components
Many novel donor–acceptor copolymers have been synthesized in the past few years, and have promoted a rapid development of high performance bulk heterojunction organic solar cells
Summary
Bulk heterojunction (BHJ) organic photovoltaic (OPV) devices employing conjugated polymers as electron donors and fullerene derivatives as electron acceptors convert the energy of sunlight into electrical current using the photovoltaic effect.[1,2] The ability to process an OPV device partly from solution makes them a promising low-cost technology for solar energy. Therea er, he joined the research group of Professor David Lidzey at the University of Sheffield (UK) to study for his Ph.D. in Organic Semiconductor Physics, which was awarded in 2012 His post-graduate research focussed on the rational understanding of common processing techniques used in the fabrication of polymer:fullerene blend lms for solar cell applications. Molecular mixing of fullerenes may in principle disrupt the packing of an amorphous polymer, such effects are o en difficult to con rm using X-ray diffraction techniques alone due to the low level of polymer crystallinity.[35] The in uence of fullerene derivative structure on the morphology and photovoltaic performance of copolymer:fullerene blend lms will be discussed in detail later in this Review. The impact of molecular structure of D–A copolymers on energy level, band-gap, charge mobility, molecular packing and photovoltaic device performance
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