acceptors have garnered extensive interest due to their benefits of the simple device structure, lightweight, flexibility, and low manufacturing cost using printing technologies. [1][2][3][4] Rapid material development and device-engineering advancement in the BHJ PSC community has resulted in a major increase in PSC performance over the past few decades, culminating in substantial breakthroughs in power conversion efficiencies (PCEs), which now exceed 18%. [5][6][7] Despite the success of the field of PSCs, batch-to-batch differences in molecular weight of a conjugated polymer used as one of the active layer components within a BHJ active layer, led to inconsistency in macromolecular ordering, optoelectronic and charge transport characteristics, and ultimately device performance. [8][9][10][11] There have been several attempts to overcome the molecular weight limitations caused by synthetic polymers. For example, You's and Marks's groups independently demonstrated the possibility of controlling polymer's molecular weight via a synthetic strategy based on the classic Carothers equation, considering the comonomer ratios and degree of polymerization. [12,13] We recently established a successful stepwise polymerization methodology for synthesizing high-quality polymers with narrow polydispersity and high molecular weight. [14] McCulloch et al. also isolated polymer fractions with well-defined molecular weights and narrow polydispersity using reparative-scale recycling size exclusion chromatography (rec-SEC). [15] These findings are useful in improving batch-to-batch reproducibility. To execute these technologies successfully, the reactant monomers and palladium (Pd) catalysts must be rigorously purified via multiple purification technologies and precisely weighed to ensure proper stoichiometric balance; otherwise, fractionation via the rec-SEC equipment must be tailored to the polymers produced, making it difficult to use in large-scale production. Hence, such methods are commercially inefficient and nonproductive.In this study, effective mathematical equations capable of achieving polymer batches with controlled molecule weights have been formulated. A series of PM6 donor polymers with varying molecular weights was prepared at different reaction times to verify the equations' effectiveness. Polymers with A major difficulty in the polymer solar cell (PSC) community is discovering a methodology capable of accessing polymeric photovoltaic materials with controllable/predictable molecular weights. Effective mathematical equations that enable the reproduction of polymer batches with precisely controlled molecular weight, by mixing as-synthesized polymer batches with the ones that have different molecular weights, are formulated in this study. The properties of both the as-synthesized and mixed-different-molecular weight PM6 polymer series are systematically investigated to determine the effect of molecular weight on the performance of related PSCs. The power conversion efficiencies (PCEs) improve monotonically with an i...
Highly volatile solid additives have attracted much attention recently because they enhance molecular packing order and possibly solve the problems of poor reproducibility and instability of polymer solar cells (PSCs) with solvent additives. The shortcoming is that existing solid additives require thermal annealing (TA) to remove them from the active layer, leading to an increase in the complexity of the device fabrication process and morphology rearrangement problems. This study introduces a commercially available, low-cost, and highly volatile material, naphthalene (NA), as a solid additive used in PSCs based on PM6: Y6. NA is well mixed with a non-fullerene acceptor and can restrict excessive aggregation of the donor and acceptor, producing efficiencies comparable to PSCs processed by 1-chloronaphthalene (CN) solvent additive. As a result, a maximum power conversion efficiency (PCE) of 16.52% for NA-processed PSC is achieved, higher than that of a PCE of 16.07% for CN-processed PSC with TA. NA-processed PSCs exhibit comparable efficiencies (PCE of 16.10%) without TA treatment and higher reproducibility/stability than CN-processed PSCs. This study demonstrates a low-cost and excellent volatile solid additive to improve the device performance and the potential for exploring new solid additives that can readily be made volatile without TA.
Modifying the end-capping groups in nonfullerene acceptors
(NFAs)
is an effective strategy for modulating their properties and that
of the entire NFAs. This study reports the synthesis of a novel γ-ester-functionalized
IC end-capping group (IC-γe) and its incorporation into the
benzothiadiazole-fused central core, yielding isomer-free IC-γe
end-capped NFAs, such as Y-IC-γe, Y-FIC-γe, and Y-ClIC-γe.
The resultant NFAs exhibited similar absorption profiles but upshifted
the lowest unoccupied molecular orbital energy level compared with
those of the ester-free analogues, such as Y6 and Y7. Without thermal
annealing, an excellent power conversion efficiency (PCE) of 16.4%
is realized in the annealing-free OSC based on Y-FIC-γe with
the PM6 donor polymer, which outperforms the OSCs based on Y-IC-γe
and Y-ClIC-γe. In addition, the OSCs based on asymmetric Y-FIC-γe
and Y-ClIC-γe have higher thermal stability with more than 83%
PCE retention at an elevated temperature after 456 h than the symmetric
Y-IC-γe case. In this study, we not only establish the structure–property
relationship regarding the ester functionality and symmetricity tuning
on the NFAs but also diagnose the reasons for the best-performing
Y-FIC-γe-based OSCs, providing useful information for a novel
high-performing NFA design strategy.
Layer-by-layer (LBL) processing approach is recently under intensive investigation to fabricate efficient polymer solar cells (PSCs) reconsidering its many positive aspects over bulk-heterojunction configuration. Moreover, with recently reported successful solid...
The industrial-scale, uniform film production of active layers is a prerequisite for high-performance, reproducible organic solar cells (OSCs), becoming a significant challenge. Blade coating, one of the most suitable protocols...
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