Nowadays, organic solar cells (OSCs) with Y6 and its derivatives as electron acceptors provide the highest efficiencies among the studied binary OSCs. To further improve the performances of OSCs, the ...fabrication of ternary OSCs (TOSCs) is a convenient strategy. Essentially, morphology control and the trade-off between voltage and photocurrent are the main critical issues in TOSCs. Herein, we address these problems by constructing TOSCs where an alloy-like composite is formed between Y6 and a newly designed derivative, BTP-M. Employing an electron-pushing methyl substituent as a replacement for the electron-withdrawing F atoms on Y6, BTP-M shows higher energy levels and lower crystallinity than Y6. As a result, the obtained Y6:BTP-M alloy can simultaneously optimize energy levels to reduce energy loss as well as the morphologies of the active layers to favor photocurrent generation, leading to an enhanced open-circuit voltage (
V
oc
) of 0.875 V together with a larger short-circuit current density (
J
sc
) of 26.56 mA cm
−2
for TOSCs based on the polymer donor PM6 and Y6:BTP-M acceptor alloy. Consequently, a best efficiency of 17.03% is achieved for the corresponding TOSCs, which is among the best values for single-junction OSCs. In addition, our TOSCs also exhibit good thickness tolerance, and can reach 14.23% efficiency even though the active layer is as thick as 300 nm.
An alloy-like model based on Y6 and its derivative BTP-M is constructed to fabricate ternary organic solar cells, leading to a best efficiency of 17.03%.
The low band gap polymer based on benzodithiophene （BDT）-thieno3,4-bthiophene （TT） backbone, PBDT-TS 1, was synthe- sized following our previous work and the bulk heterojunction （BHJ） material ...comprising PBDT-TS 1/PC71BM was optimized and characterized. By processing the active layer with different additives i.e. 1,8-diiodooctane （DIO）, 1-chloronaphthalene （CN） and 1, 8-octanedithiol （ODT） and optimizing the ratio of each additive in the host solvent, a high PCE of 9.98% was obtained under the condition of utilizing 3% DIO as processing additive in CB. The effect of varied additives on photovoltaic perfor- mance was illustrated with atomic force microscopy （AFM） and transmission electron microscope （TEM） measurements that explained changes in photovoltaic parameters. These results provide valuable information of solvent additive choice in device optimization of PBDTTT polymers, and the systematic device optimization could be applied in other efficient photovoltaic polymers. Apparently, this work presents a great advance in single junction PSCs, especially in PSCs with conventional architecture.
A novel non‐fullerene acceptor, possessing a very low bandgap of 1.34 eV and a high‐lying lowest unoccupied molecular orbital level of −3.95 eV, is designed and synthesized by introducing ...electron‐donating alkoxy groups to the backbone of a conjugated small molecule. Impressive power conversion efficiencies of 8.4% and 10.7% are obtained for fabricated single and tandem polymer solar cells.
Organic solar cells (OSCs) can be unstable under ultraviolet (UV) irradiation. To address this issue and enhance the power conversion efficiency (PCE), an inorganic‐perovskite/organic four‐terminal ...tandem solar cell (TSC) based on a semitransparent inorganic CsPbBr3 perovskite solar cell (pero‐SC) as the top cell and an OSC as bottom cell is constructed. The high‐quality CsPbBr3 photoactive layer of the planar pero‐SC is prepared with a dual‐source vacuum coevaporation method, using stoichiometric precursors of CsBr and PbBr2 with a low evaporation rate. The resultant opaque planar pero‐SC exhibits an ultrahigh open‐circuit voltage of 1.44 V and the highest reported PCE of 7.78% for a CsPbBr3‐based planar pero‐SC. Importantly, the devices show no degradation after 120 h UV light illumination. The related semitransparent pero‐SC can almost completely filter UV light and well maintain photovoltaic performance; it additionally shows an extremely high average visible transmittance. When it is used to construct a TSC, the top pero‐SC acting as a UV filter can utilize UV light for photoelectric conversion, avoiding the instability problem of UV light on the bottom OSC that can meet the industrial standards of UV‐light stability for solar cells, and leading to the highest reported PCE of 14.03% for the inorganic‐perovskite/organic TSC.
A wide‐bandgap and low‐defect‐concentration CsPbBr3 film is fabricated using the vacuum‐evaporation method, and the related solar cell shows a high efficiency and robust photostability. When constructing inorganic‐perovskite/organic tandem solar cells, the top CsPbBr3‐based semitransparent perovskite solar cells can be used to filter ultraviolet (UV) light and overcome the UV‐light stability problem of the organic solar cells; they also show a record efficiency of 14.03%.
Most of the high-performance organic solar cells are fabricated with the assistance of high-boiling-point solvent additives to optimize their charge transport properties; this has adverse effects on ...the OSCs' stability and reproducibility in large-scale production. Here, we design volatilizable solid additives by considering the molecular structure feature of an acceptor-donor-acceptor-type non-fullerene acceptor. The application of solid additives can enhance the intermolecular π-π stacking of the non-fullerene acceptor and thus facilitate the charge transport properties in the active layers, leading to improved efficiencies of OSCs. Importantly, devices fabricated using volatilizable solid additives exhibit higher stability and reproducibility when compared with the OSCs processed with solvent additives. Our results not only demonstrate an approach of applying volatilizable solid additives to benefit the large-scale production of OSCs but also provide a potential direction for designing specific solid additives for different active layers.
Ternary blending and copolymerization strategies have proven advantageous in boosting the photovoltaic performance of organic solar cells. Here, 15% efficiency solar cells using copolymerization ...donors are demonstrated, where the electron‐withdrawing unit, ester‐substituted thiophene, is incorporated into a PBDB‐TF polymer to downshift the molecular energy and broaden the absorption. Copolymer‐based solar cells suitable for large‐area devices can be fabricated by a blade‐coating method from a nonhalogen and nonaromatic solvent mixture. Although ternary solar cells can achieve comparable efficiencies, they are not suitable for environment‐friendly processing conditions and show relatively low photostability compared to copolymer‐based devices. These results not only demonstrate high‐efficiency organic photovoltaic cells via copolymerization strategies but also provide important insights into their applications in practical production.
Organic solar cells achieve over 15% efficiency through the use of a copolymer donor, and simultaneously enhanced open‐circuit voltage and short‐circuit current density are obtained. High‐performance solar cells are adaptable for environment‐friendly solvents using a blade‐coating method, while showing better photostability than the corresponding ternary solar cells.
Herein, we investigated a series of fullerene-free organic solar cells (OSCs) based on six different donor:acceptor (D:A) blends with varied highest occupied molecular orbital (HOMO) offsets from ...−0.05 to 0.21 eV. First, to verify the energetic compatibility of a specific D:A pair, especially for HOMO offsets, we established a simple method to estimate the hole transfer tendencies between D and A by using bilayer hole-only devices. It reveals that the asymmetrical diode effect of the bilayer hole-only devices can correlate with the FF and J sc of the relevant OSCs. Second, to find out whether HOMO offset is the main restriction of hole transfer, we measured transient absorption spectra and examined the hole transfer behavior in the blends, revealing that the occurrence of hole transfer is independent of the HOMO offsets and ultrafast in the time scale of ≤4.6 ps for those blends with ≥0 eV HOMO offsets. In contrast, a negative HOMO offset can significantly slow down the hole transfer with a half-time of ∼400 ps. Furthermore, we compare the device parameters under varied light intensities and discover that the bimolecular recombination should be one of the main restrictions for high device performance. Surprisingly, small HOMO offsets of 0 and 0.06 eV can also enable high PCEs of 10.42% and 11.75% for blend 2 (PTQ10:HC-PCIC) and blend 3 (PBDB-TF:HC-PCIC), respectively. Overall, our work demonstrates not only the validity of high-performance OSCs operating at the near zero HOMO offsets but also the charge dynamic insights of these blends, which will help gain understanding on the further improvement of OSCs.
A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (E g ...opt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of −5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (V oc = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor–acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.
Recently, the benzodithiophene- (BDT-) based polymers with conjugated side groups attracted considerable attention due to their superior properties in polymer solar cells (PSCs), so the investigation ...of the side chain effects on the photovoltaic properties of this type of polymers is an interesting and important topic for molecular design. Herein, three conjugated polymers based on BDT and thieno3,4-bthiophene units with furan, thiophene and selenophene as side groups, named as PBDTTT-EFF, PBDTTT-EFT, and PBDTTT-EFS, were synthesized and applied in polymer solar cells. The polymers were characterized in parallel by absorption spectroscopy, thermogravimetric analysis (TGA), density functional theory (DFT), ultraviolet photoemission spectroscopy (UPS), X-ray diffraction (XRD), and photovoltaic measurements. The results show that the dihedral angles between the BDT and conjugated side groups play important roles in affecting the absorption bands, HOMO levels, crystallinities, and aggregation sizes of the polymers. The photovoltaic results indicate that PBDTTT-EFT and PBDTTT-EFS show similar photovoltaic characteristics in device, and PCEs of 9.0% and 8.78% were obtained, respectively. The device of PBDTTT-EFF shows a V oc of 0.69 V and a J sc of 11.77 mA/cm2, which are lower than those in the devices based on the other two polymers. Overall, this work suggests that the photovoltaic properties of the BDT-based polymers can be effectively tuned by introducing conjugated side groups with varied steric hindrance.
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