The power conversion efficiencies (PCEs) of organic solar cells (OSCs) have improved considerably in recent years with the development of fused-ring electron acceptors (FREAs). Currently, FREAs-based OSCs have achieved high PCEs of over 19% in single-junction OSCs. Whereas the relatively high synthetic complexity and the low yield of FREAs typically result in high production costs, hindering the commercial application of OSCs. In contrast, noncovalently fused-ring electron acceptors (NFREAs) can compensate for the shortcomings of FREAs and facilitate large-scale industrial production by virtue of the simple structure, facile synthesis, high yield, low cost, and reasonable efficiency. At present, OSCs based on NFREAs have exceeded the PCEs of 15% and are expected to reach comparable efficiency as FREAs-based OSCs. Here, recent advances in NFREAs in this review provide insight into improving the performance of OSCs. In particular, this paper focuses on the effect of the chemical structures of NFREAs on the molecule conformation, aggregation, and packing mode. Various molecular design strategies, such as core, side-chain, and terminal group engineering, are presented. In addition, some novel polymer acceptors based on NFREAs for all-polymer OSCs are also introduced. In the end, the paper provides an outlook on developing efficient, stable, and low-cost NFREAs for achieving commercial applications.
Comprehensive Summary
Bithiophene imide (BTI)‐based polymers have been promising photovoltaic materials due to their high mobility and tunable energy levels. However, BTI polymers have rarely been revisited since organic solar cells (OSCs) entered the era of non‐fullerene electron acceptors (NFEA) likely owing to their incompatibility with NFEAs. Herein, fine‐tuning the aggregation and orientation of BTI‐based donor‐π‐acceptor (D‐π‐A) polymer donors was achieved by incorporating the linear n‐octyl group into thiophene π‐bridge. The resulting polymer donor G15 shows excellent compatibility with NFEA L15 (polymer acceptor). The G15‐based all‐polymer OSCs achieve high power conversion efficiency of 15.17%. This is significantly higher than that (< 5%) of its analogue with isomerized branched alkyl chains and also among the highest values for all‐polymer OSCs. The results highlight that well‐tailored BTI polymer donors are attractive photovoltaic materials for further exploration in non‐fullerene organic solar cells.
Hole transport materials (HTMs) are of great significance to improve the efficiency and long-term stability of perovskite solar cells (PVSCs). Herein, a series of new HTMs based on isomeric dithienothiophene (DTT) are designed and synthesized. Effects of sulphur (S) atoms positions on defect passivation and performance of PVSCs are systematically investigated through theoretical computation, X-ray diffraction, X-ray photoelectron spectroscopy, etc. The three molecules display noticeable isomeric effect in energy level, light absorption, and hole mobility. With S atoms varied from bottom-bottombottom in 3T-1 to bottom-bottom-top in 3T-2, then to bottom-top-bottom in 3T-3, the grown perovskite crystallite on the corresponding HTMs shows more homeogenous film morphology and less pinhole traps. Meanwhile, nonradiative recombination losses can be suppressed and hole extraction efficiency at HTM/perovskite surface can be improved from 3T-1 to 3T-3. As a result, the remarkable improvement of short-circuit current density nd open-circuit voltage in inverted perovskite solar cells can be realized with increasing the sulphur atoms contribution to the molecular conjugation. More importantly, 3T-3-based dopant-free HTM achieves a top power conversion efficiency of 19.23% in PVSCs with good device stability under green solvent processing. These results demonstrate the role of S atoms positions in HTMs on photovoltaic performance of PVSCs and the potential of DTT in developing eco-friendly HTMs toward efficient PVSCs.
Polymerized small molecule acceptors have recently greatly facilitated the development of all‐polymer solar cells (All‐PSCs) with respect to the power conversion efficiencies (PCEs). However, high‐performance and low‐cost polymer donors for All‐PSCs are still lacking, limiting further large‐scale manufacturing of All‐PSCs. Herein, this work designs and synthesizes a new thiophene derivative, FETVT, featuring vinyl‐bridged fluorine and ester‐substituted monothiophene. Incorporation of FETVT into a polymer yields a high‐performance polythiophene derivative PFETVT‐T, which exhibits deep‐lying HOMO level, suitable solution pre‐aggregation ability, finely‐tuned polymer crystallinity, and appropriate thermodynamic miscibility with the polymer acceptor L15. As a result, binary based on PFETVT‐T achieves a record PCE of 11.81% with agood stability, representing a breakthrough for polythiophenes and their derivatives‐based All‐PSCs, which is also significantly higher than that (1.92%) of All‐PSCs based on its isomerized analog. Remarkably, PFETVT‐T achieves an impressive PCE exceeding 16% via the implementation of a ternary blend design. These findings offer a hopeful pathway toward attaining high‐performance, stable, and cost‐effective PSCs.
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