Completely nonfused electron acceptors for organic photovoltaic cells
Organic photovoltaic(OPV)cells have attracted considerable attention as a renewable energy technology,owing to their outstanding advantages of flexibility,light weight,and ease of manufacturing large-area panels through low-cost solution coating processes.With the rapid development of photovoltaic materials,especially the innovation of fused non-fullerene acceptors with an acceptor-donor-acceptor structure,the power conversion efficiency(PCE)of single-junction OPV cells has successfully exceeded 20％.The fused central unit can maintain the planarity and rigidity of the conjugated backbone,which in turn enhances intramolecular π-electron delocalization and intermolecular π-π stacking.However,the synthesis routes of the fused conjugated backbones are often long and tedious,leading to high preparation costs for OPV cells;this has severely impeded the industrialization of OPV technology.Therefore,the development of low-cost nonfused acceptors has become an important topic within the OPV field.In the recent past,research on completely non-fused acceptors has made considerable progress.In terms of chemical structure,these nonfused acceptors are composed of a central donor unit,two terminal groups,and non-conjugated side chains.The donor unit chiefly consists of aromatic rings,such as benzene and thiophene,which are connected by C-C single bonds.In addition,selenophene,thiazole,and pyrrole are introduced as building units into the conjugated skeleton.The majority of terminal units are 2-(3-oxo-2,3-dihydro-1H-indene-1-yl)acetonitrile(IC)or halogen-substituted IC terminal groups.In this review,first,we classify and summarize the reported completely nonfused acceptors according to the number of aromatic rings in the donor units.Most of the reported acceptors are based on three and four aromatic ring structures,and some acceptors are based on two and five aromatic ring structures.Second,we aim to provide valuable reference and guidance for the design of high-performance nonfused acceptors by focusing on the structural changes of the molecular conjugated backbone,side chains,and end groups,followed by thoroughly discussing the correlation between the molecular structure,material properties,and photovoltaic performance.In addition,we comment on the development and challenges of materials from the aspects of efficiency,cost,and stability.By introducing two common molecular design strategies,intramolecular non-covalent interactions and large steric hindrance side chains,the PCEs of OPV cells based on fully nonfused acceptors have rapidly increased from the initial 5％to 17％,thus showing great application potential.At the same time,preliminary correlations between the chemical structure,physical properties,film morphology,and device performance have been constructed,which can provide valuable guidance for the design of high-performance nonfused acceptors.In the future,it is expected that through further innovation,molecular design strategy will achieve an efficiency breakthrough of over 20％as well as surpass the current efficiency of OPV cells based on fused acceptors.In addition,by developing low-cost end groups,the overall cost of the materials can be effectively reduced.Accordingly,we propose using machine learning technology to screen and optimize existing material structures to guide the synthesis of new materials and accelerate the innovation and development of OPV technology.Finally,it should be noted that the structures of the donor materials required to prepare nonfused acceptors-based OPV cells are mostly complex,which restricts the practical application of OPV technology.Therefore,developing low-cost donors that match these nonfused acceptors is also crucial.
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维普
