Benzothiadiazole-based non-fullerene acceptors

Harnessing energy from the sun is attracting increasing attention as the traditional fossil-based energy sources are being depleted. Photovoltaics (PV) is now an established technology and the most promising method...

Recent Progress in Organic Solar Cells Based on Non-Fullerene Acceptors: Materials to Devices

Ternary organic solar cells based on non-fullerene acceptors: A review

Organic photovoltaic (OPV) cells have recently undergone a rapid increase in power conversion efficiency (PCE) under AM1.5G conditions, as certified by the National Renewable Energy Laboratory (NREL), which have jumped from 11.5% in October 2017 to 18.2% in December 2020. However, the NREL certified PCE of large area OPV modules is still lagging far behind (11.7% in July 2020). Additionally, there has been a rapidly growing interest in the use of OPVs for dim light indoor applications, with reported PCE of some large area (≥1 cm2) devices, under 1000 lux, well above 20%. The transition of OPV from the lab to the market requires the development of effective manufacturing processes that can scale‐up laboratory‐scale devices into large area devices, without sacrificing performance and simultaneously minimizing associated manufacturing costs. This review article focuses on four important challenges that OPV technology has to face to achieve a reliable lab‐to‐fab transfer, namely: i) The upscaling of indium‐tin‐oxide (ITO)‐based single cells and the interconnection of single cells into large area modules; ii) the development of alternatives to vacuum processing; iii) the development of alternatives to ITO‐based substrates; and iv) strategies for improving the lifetime of large area OPV devices.

Progress in Upscaling Organic Photovoltaic Devices

The ternary blending strategy of introducing a third component into binary organic solar cells (BOSCs) is a feasible and efficient strategy to optimize the performance of BOSCs. Ternary organic solar cells (TOSCs) have an adjustable absorption band for matching the solar light characteristics, easily adjustable photoelectric performance and tunable micro-morphology; therefore, they have become a hotspot in the field of OSC research. Currently, the power conversion efficiency (PCE) of TOSCs has been boosted over 17%. Herein, we give a review on the four possible working mechanisms of TOSCs, roles of the third component in TOSCs, recent progress made in different kinds of active layer materials of TOSCs based on solution-processed non-fullerene acceptors (NFAs), and recent advances in large-area TOSCs and their long-term stability. This review can provide some guidance for the further development of TOSCs. Finally, to help researchers understand the future of TOSCs, the challenges and prospects of TOSCs based on solution-processible NFAs have been provided.

Recent progress in ternary organic solar cells based on solution-processed non-fullerene acceptors

It is challenging to afford efficient and stable organic solar cells based on an as-cast active layer without any external treatments. We present a planar organic electron acceptor, BPTCN, with high electron mobility as a third component in nonfullerene ternary polymer solar cells, which comprises an electron-deficient 4,7-bis(5H-4,6-dioxothieno[3,4-c]pyrrol-1-yl)benzo[c][1,2,5]thiadiazole core, doubly endcapped by 2-(3-ethyl-5-methylene-4-oxothiazolidin-2-ylidene)malononitrile through the alkylated thiophene-2,5-ylene unit. It shows a π–π stacking distance of 3.60 A and μe of 1.31 × 10−3 cm2 V−1 s−1. BPTCN exhibits an absorption maximum at 569 nm in the as-cast film and good miscibility with the NIR-absorption acceptor COi8DFIC, leading to complete forster energy transfer in the blends. Adding BPTCN into the PTB7-Th:COi8DFIC blend produces multiple beneficial effects: (i) facilitating exciton dissociation and charge transfer at the donor/acceptor interface while suppressing bimolecular and trap-assisted recombination, as revealed by analysis of the Jph–Veff, Jsc–Ilight and Voc–Ilight characteristics, (ii) increasing hole and in particular electron transport; and (iii) generally promoting the crystallinity of the polymer donor PTB7-Th, as revealed by grazing incidence X-ray diffraction results. Moreover, the phase purity is greatly improved in the ternary blend PTB7-Th : COi8DFIC : BPTCN (1 : 1.05 : 0.45 by weight). Consequently, the tentatively optimized ternary solar cell provides a PCE of 11.62% with a Voc = 0.74 V, Jsc = 25.93 mA cm−2 and FF = 60.61% in comparison with the binary systems PTB7-Th:COi8DFIC (PCE of 9.41%) and PTB7-Th:BPTCN (6.42%) in the absence of any extra treatments. After thermal aging at 80 °C for 450 h, this ternary solar cell exhibits increased stability with the PCE retaining 84.39% of the initial value.

Enhanced efficiency and stability of nonfullerene ternary polymer solar cells based on a spontaneously assembled active layer: the role of a high mobility small molecular electron acceptor

Fine-tuning the alkyl chains and end groups of non-fused ring electron acceptors (NFREAs) plays vital roles in the promotion of charge transfer (CT) and power conversion efficiency (PCE). In this work, we developed a series of A-D-A'-D-A-type NFREAs, which possess the same terminals (A), the cyclopentadithiophene unit (D), and the thieno[3,4-c]pyrrole-4,6-dione (A'). Despite the subtle difference in side chains and halogenated end groups, the six acceptors exhibit a considerable difference in the efficiency and device stability of the organic solar cells (OSCs). Among the molecules, chlorinated NFREAs show a broader light absorption than the fluorinated ones do. Compared with C8C8-4F (1-octylnonyl and fluorination) and C6C4-4Cl (2-butyloctyl and chlorination), C8C8-4Cl (1-octylnonyl and chlorination) exhibits a lower highest occupied molecular orbital level, higher electron mobility, and denser molecular packing. The OSCs based on PM6:C8C8-4Cl yield the best PCE of 14.11%, which is attributed to the faster charge transport, high miscibility, and preferable morphology. Moreover, the PM6:C8C8-4Cl devices retain 91.1% of the initial PCE after being placed in air with 67% relative humidity for 50 days. This work shows that the simultaneous optimization of side chains and end groups facilitates the CT and improves the stability in the OSCs, offering a novel view into the molecular design of A-D-A'-D-A-type NFREAs.

Simultaneous Tuning of Alkyl Chains and End Groups in Non-fused Ring Electron Acceptors for Efficient and Stable Organic Solar Cells.

Dual-Functional Ambipolar Non-Fused Ring Electron Acceptor as Third Component and Designing Similar Molecular Structure between Two Acceptors for High-Performance Ternary Organic Solar Cells

Dou Luo

Papers

Recent Progress in Organic Solar Cells Based on Non-Fullerene Acceptors: Materials to Devices

Enhanced efficiency and stability of nonfullerene ternary polymer solar cells based on a spontaneously assembled active layer: the role of a high mobility small molecular electron acceptor

Simultaneous Tuning of Alkyl Chains and End Groups in Non-fused Ring Electron Acceptors for Efficient and Stable Organic Solar Cells.

Dual-Functional Ambipolar Non-Fused Ring Electron Acceptor as Third Component and Designing Similar Molecular Structure between Two Acceptors for High-Performance Ternary Organic Solar Cells

1+1>2: Dual Strategies of Quinolinic Acid Passivation and DMF Solvent Annealing for High-Performance Inverted Perovskite Solar Cell