Achieving and Understanding of Highly Efficient Ternary Organic Photovoltaics: From Morphology and Energy Loss to Working Mechanism

Abstract

design and device configuration innovation, the power conversion efficiencies (PCEs) of OPVs have been boosted rapidly in the recent few years. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] Currently, the most advanced OPVs are based on Y-series non-fullerene acceptors (NFAs), for which a series of molecular structure optimizations, including alkyl chain tuning, [24,25] asymmetric terminals, [12,[26][27][28] and heteroatom exchanging, [29,30] are explored, and various ternary or tandem devices are also developed to advance the PCEs to exceed 19% for single-junction devices and 20% for tandem devices, [31][32][33][34][35][36] thus speeding up the progress for the industrialization of OPVs. [37] For OPV devices, the whole working process for photon-to-electron conversion includes five steps: 1) exciton generation after light absorption; 2) exciton diffusion to donor/acceptor (D/A) interfaces; 3) exciton dissociation into free charges; 4) free charge transport to buffer layers; 5) charge collection by the electrodes. [38] Among them, the intermediate three steps, which all face the big issue of charge recombination, mainly govern the achievement of high efficiencies. [39][40][41] Generally, exciton diffusion is correlated with domain sizes and exciton lifetimes, exciton dissociation is related with interface abundance and driving force, while charge transport is affected by molecular orientation and charge mobility. [42][43][44] And all above mentioned factors point to the same key topic: morphology control, [45] which can be modulated by tuning the photovoltaic material properties, for example, temperature-dependent aggregation for polymer donors, [46,47] dominant face-on orientation of small molecule acceptors, [48,49] or applying post-treatments including thermal annealing, solvent additive, etc. [50][51][52][53] Besides, utilizing ternary blend by introducing a third component is another effective and convenient way to achieve morphology control for higher efficiencies. [54][55][56] The well-refined active layer morphology may be equipped with some of the following features: bi-continuous interpenetrating network, modest domain sizes, defined vertical phase separation, fibril-like form, etc. [35,[57][58][59][60] In device parameters, through morphology control, short-circuit current density (J sc ) and fill factor (FF) can be managed significantly, while the open-circuit voltage (V oc ) is heavily dependent on the energy loss (E loss ). [61] Different from inorganic solar cells, the tightly Coulombic bounded Frenkel excitons in OPVs bring a critical problem that Ternary strategy, adding an additional donor (D) or acceptor (A) into conventional binary D:A blend, has shown great potential in improving photovoltaic performances of organic photovoltaics (OPVs) for practical applications. Herein, this review is presented on how efficient ternary OPVs are realized from the aspects of morphology, energy loss, and working mechanism. As to morphology, the role of third component on the formation of...

Diffusion‐Limited Accepter Alloy Enables Highly Efficient and Stable Organic Solar Cells

“…The CV characterization shows that the onset oxidation/reduction potentials (ϕ ox /ϕ red ) of Y6, Y6: ZCCF3, and ZCCF3 specimens are 1.31 V/-0.34 V, © 2023 Wiley-VCH GmbH 1.30 V/-0.43 V, and 1.29 V/-0.48 V, respectively, yielding their corresponding E HOMO /E LUMO of -5.65 eV/-4.00 eV, -5.64 eV/-3.91 eV, -5.63 eV/-3.86 eV (Figure 2b, Table 1). The results suggest that the structural torsion of ZCCF3 leads to a different electronic effect in both neat and dual acceptor blend, and its diazepine group can raise LUMO energy level to help boost the V OC output in OSCs, [43] consistent with the proposed molecular geometry aforementioned.…”

Symmetry breaking: an efficient structure design of nonfullerene acceptors to reduce the energy loss in organic solar cells

“…18,[52][53][54][55][56] These results strongly imply that the molecular structures of NFAs and their molecular packing behaviors in the solid state play critical roles in determining the E loss and the final device performance. In this regard, new structural optimization strategies for FREAs have been continuously explored to further reduce the E loss , 15,57 among which symmetry breaking has recently been proven as an effective strategy. Compared to the symmetric structure, asymmetric structural design can endow the resulting FREAs with a larger dipolar moment and an enhanced intermolecular binding energy, leading to intensified intermolecular interactions and increased packing order, both of which are desired for suppressing NRR loss.…”

Refined molecular microstructure and optimized carrier management of multicomponent organic photovoltaics toward 19.3% certified efficiency

“…[31][32][33] In addition, a multicomponent strategy introducing extra donor or acceptor components to binary systems is commonly used to improve the carrier dynamics and device parameters, especially in pursuing a higher V oc . [34][35][36][37][38][39][40][41] However, how the extra component combines with the host materials at the nanoscale level is not yet well understood, building barriers to acquiring design rules for successful multicomponent blends. 42 In summary, the field of nanoscale study on interfaces is still blank but is critical to the exploration of successful multicomponent systems with comprehensive carrier management, particularly with non-radiative recombination loss mitigation.…”