Wentao Xiong

Ternary Organic Solar Cells Based on Two Compatible Nonfullerene Acceptors with Power Conversion Efficiency >10%

Two different nonfullerene acceptors and one copolymer are used to fabricate ternary organic solar cells (OSCs). The two acceptors show unique interactions that reduce crystallinity and form a homogeneous mixed phase in the blend film, leading to a high efficiency of ≈10.3%, the highest performance reported for nonfullerene ternary blends. This work provides a new approach to fabricate high-performance OSCs.

Non-planar perylenediimide acceptors with different geometrical linker units for efficient non-fullerene organic solar cells

Three perylenediimide (PDI) acceptors (P2O2, P2N2 and P4N4) were synthesized by functionalizing the bay positions of PDI with benzil, 2,3-diphenylquinoxaline and 2,3,7,8-tetraphenylpyrazino[2,3-g]quinoxaline as linkers, respectively. The photovoltaic properties of the three acceptor molecules have been investigated. The different PDI linker units show different physical and chemical properties of the PDIs. The three PDIs display different non-planar geometrical structures because of the different linker units, which affect the corresponding morphology of the blend films and also influence the charge mobility and fill factor (FF) of the organic solar cells (OSCs). Furthermore, the gradient energy levels of the three PDIs provide an efficient research model for the relationship of device open-circuit voltage (Voc) and energy levels. As the result, the P4N4 based non-fullerene devices show the best photovoltaic performance with a power conversion efficiency (PCE) of 5.71%, whereas the P2O2 and P2N2 based non-fullerene devices show relatively lower PCEs of 2.53% and 3.86%, respectively.

Influence of 2,2-bithiophene and thieno[3,2-b] thiophene units on the photovoltaic performance of benzodithiophene-based wide-bandgap polymers

Extending the π-conjugation length of the polymeric backbone is an effective way to enhance the photovoltaic performance of polymer solar cells (PSCs). Here, the donor–donor–acceptor (D–D–A) molecular strategy has been used to design and synthesize two wide-bandgap conjugated copolymers, in which 2,2-bithiophene (BT) or thieno[3,2-b] thiophene (TT) is introduced to the D–A polymer as a third component to investigate the influence of the conjugation backbone on photovoltaic properties. The structure–property relationship and photovoltaic performance of the polymer have been investigated. Compared to P2 (TT as the third unit), P1 (BT as the third unit) exhibits a deeper highest occupied molecular orbital (HOMO) level and a more planar backbone structure with slightly higher mobility. Based on a conventional device structure with PC70BM as the acceptor material, P1-based solar cells exhibit a maximum power conversion efficiency (PCE) of 6.93%, an open-circuit voltage (VOC) of 0.86 V, a short-circuit current (JSC) of 11.06 mA cm−2, and a fill factor (FF) of 72.9%, which are much better than those of P2-based solar cells (PCE 3.92%). These results demonstrate that extending the effective π-conjugation structure of the polymer backbone could improve the photovoltaic performance of PSCs by inserting an additional appropriate donor unit in the D–A polymer.