Energy Level Tuning of Non-Fullerene Acceptors in Organic Solar Cells (original) (raw)
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Research Article, 2022
Four Acceptor-Donor-Accepter (A-D-A) type of triangular shaped sub-phthalocyanines (SubPcs) donor molecules namely SubPcs-EDM (sub-phthalocyanines-ethylidene di-malononitrile as M1), SubPcs-ETFM (sub-phthalocyanines-ethylidene tetrafluoro-malononitrile as M2), SubPcs-ETFOM (sub-phthalocyanines-ethylidene tetrafluoro-oxo malononitrile as M3) and SubPcs-EOM (sub-phthalocyanines-ethylidene oxo malononitrile as M4) have been designed for computing its optoelectronic properties with state-of-the-art density functional theory B3LYP/LanL2DZ (d, p) model. In designed molecules, the non-fullerene acceptors are attached at the center of donor moieties. The SubPcs-ETFOM exhibited lowest band gap of energy 2.48 eV with broad absorption band at 645.53 nm. The open circuit voltage (V OC) of M3 is 2.55 V in comparison with phenyl-C 60-butyric acid methyl ester which abbreviated as PCBM. This computational study explains that engineered molecules
Enabling low voltage losses and high photocurrent in fullerene-free organic photovoltaics
Nature Communications
Despite significant development recently, improving the power conversion efficiency of organic photovoltaics (OPVs) is still an ongoing challenge to overcome. One of the prerequisites to achieving this goal is to enable efficient charge separation and small voltage losses at the same time. In this work, a facile synthetic strategy is reported, where optoelectronic properties are delicately tuned by the introduction of electron-deficient-core-based fused structure into non-fullerene acceptors. Both devices exhibited a low voltage loss of 0.57 V and high short-circuit current density of 22.0 mA cm −2 , resulting in high power conversion efficiencies of over 13.4%. These unconventional electron-deficient-core-based non-fullerene acceptors with near-infrared absorption lead to low non-radiative recombination losses in the resulting organic photovoltaics, contributing to a certified high power conversion efficiency of 12.6%.
ACS Omega, 2022
In the present work, five novel non-fullerene acceptor molecules are represented to explore the significance of organic solar cells (OSCs). The electro-optical properties of the designed A−D−A-type molecules rely on the central core donor moiety associated with different halogen families such as fluorine, chlorine, and bromine atoms and acyl, nitrile, and nitro groups as acceptor moieties. Among these, M1 exhibits the maximum absorption (λ max) at 728 nm in a chloroform solvent as M1 has nitro and nitrile groups in the terminal acceptor, which is responsible for the red shift in the absorption coefficient as compared to R (716 nm). M1 also shows the lowest value of the energy band gap (2.07 eV) with uniform binding energy in the range of 0.50 eV for all the molecules. The transition density matrix results reveal that easy dissociation of the exciton is possible in M1. The highest value of the dipole moment (4.6 D) indicates the significance of M4 and M2 in OSCs as it reduces the chance of charge recombination. The low value of λ e is given by our designed molecules concerning reference molecules, indicating their enhanced electron mobility. Thus, these molecules can serve as the most economically efficient material. Hence, all newly designed non-fullerene acceptors provide an overview for further development in the performance of OSCs.
Applied Physics Letters, 2020
Introduction of interface layers can maximize the performance of certain organic solar cells. We demonstrate that high efficiency non-fullerene acceptor based solar cells can be further improved with the insertion of PC 70 BM as an interlayer between the electron transport layer and the active layer. The combination of ZnO and PC 70 BM layers between a cathode and a bulk heterojunction active layer appears to serve as a better selective contact by reducing charge transport barrier and recombination. The enhanced short-circuit current density (J SC) is characterized by a low series-resistance (<2 X cm 2), improved charge collection efficiency, and power conversion efficiency. These features are reflected in impedance spectroscopy and electrical noise measurements and provide a route for large-area organic solar cells.
Photovoltaic properties of M-phthalocyanine/fullerene organic solar cells
Photovoltaic devices made from M-phthalocyanine and fullerene have been fabricated and characterized by current–voltage response, lateral time-of-flight photoconductivity, UV-visible absorption and scanning electron microscopy. The effect of varying the central moi-ety on the photovoltaic performance is examined, and demonstrates that the monovalent and divalent phthalocyanines tend to yield higher efficiencies in blended structures, whereas the trivalent and tetravalent phthalocyanines tend to yield higher efficiencies in a bilayer structure. The apparent reason for the disparity is the measured decrease in the hole transport efficiency in trivalent and tetravalent phthalocyanine upon blending with C 60. Furthermore, the open circuit voltages of M-phthalocyanine/fullerene solar cells are grouped together according to the valency of the central moiety.
Mapping the energy level alignment at donor/acceptor interfaces in non-fullerene organic solar cells
Nature Communications, 2022
Energy level alignment (ELA) at donor (D)-acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1-2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor-non-fullerene-acceptor systems.
ACS applied materials & interfaces, 2018
The open-circuit voltage ( V) loss has always been a major factor in lowering power conversion efficiencies (PCEs) in bulk heterojunction organic photovoltaic cells (OPVs). A method to improve the V is indispensable to achieve high PCEs. In this paper, we investigated a series of perylene diimide-based ladder-type molecules as electron acceptors in nonfullerene OPVs. The D-A ladder-type structures described here lock our π-systems into a planar structure and eliminate bond twisting associated with linear conjugated systems. This enlarges the interface energy gap (Δ E), extends electronic delocalization, and hence improves the V. More importantly, these devices showed an increase in V without compromising either the J or the FF. C5r exhibited a strong intermolecular interaction and a PCE value of 6.1%. Moreover, grazing-incident wide-angle X-ray scattering analysis and atomic force microscopy images suggested that our fused-ring acceptors showed a suitable domain size and uniform ble...