While great progress has been achieved in all-polymer solar cells (all-PSCs), the efficiency of all-PSCs is primarily limited by polymer acceptors that lack a high extinction coefficient, high electron mobility, and good compatibility with polymer donors. Here we designed and developed a polymer acceptor PFA1 based on a nonfullerene acceptor framework with a fluorine substituent on the 1,1-dicyanomethylene-3-indanone unit. In combination with an electron-donating polymer, PTzBI-oF, the blend film presents an extended and intensified absorption profile, enhanced electron mobility, and favorable film morphology. The optimized all-PSCs exhibit a remarkably high efficiency of 15.11%, which is, to the best of our knowledge, the highest performance yet reported for an all-PSC. Of particular importance is the applicability of PFA1 as a universal polymer acceptor with a range of polymer donors to achieve impressively high efficiencies. These properties enable a new molecular design strategy for the construction of polymer acceptors toward applications in high-performance all-PSCs.
Fluorine substitution has been vital to the molecular design of π-conjugated polymers toward highly efficient polymer solar cells because it results in improved intermolecular contacts. However, the understanding of how regioselectivity impacts relevant optoelectronic properties in nonsymmetric fluorinated systems remains poorly developed. In response, we herein incorporated a single fluorine atom onto the πbridge of [1,2,3]triazolo[4,5-f ]isoindole-5,7(2H,6H)-dione (TzBI)-polymers to construct two regioisomeric donors, denoted as PTzBI-dF and PTzBI-pF, and investigated how these subtle structural details impact the bulk properties of solar cells. We found that the fluorine substituent position has a profound effect on molecular conformations and thus the aggregated morphology, leading to notably different optical absorption and charge transport. The resulting polymer PTzBI-dF, with fluorine atom distal to the TzBI core, exhibited a power conversion efficiency of up to 17.3% that obviously outperforms the regioisomeric counterpart. These findings highlighted the strategic superiority of materials design toward high-performance solar cells.
Interfacial modification between the electrode and the overlying organic layer has significant effects on the charge injection and collection and thus the device performance of organic photodetectors. Here, we used copper(I) thiocyanate (CuSCN) as the anode interfacial layer for organic photodetector, which was inserted between the anode and an organic light-sensitive layer. The CuSCN layer processed with ethyl sulfide solution presented similar optical properties to the extensively used anode interlayer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), while the relatively shallow conduction band of CuSCN resulted in a much higher electron-injection barrier from the anode and shunt resistance than those of PEDOT:PSS. Moreover, the CuSCN-based device also exhibited an increased depletion width for the PEDOT:PSS-based device, as indicated by the Mott–Schottky analysis. These features lead to the dramatically reduced dark current density of 2.7 × 10–10 A cm–2 and an impressively high specific detectivity of 4.4 × 1013 cm Hz1/2 W–1 under −0.1 V bias and a working wavelength of 870 nm. These findings demonstrated the great potential of using CuSCN as an anode interfacial layer for developing high-performance near-infrared organic photodetectors.
The anode interlayer plays a critical role in the performance of organic photodetectors, which requires sufficient electron-blocking ability to simultaneously attain a high photocurrent and low dark current. Here, we developed two cross-linkable polymers, which can be deposited on the top of the widely used poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and form a robust layer that can effectively suppress the electron injection from the anode under reverse bias. The optimized device with the resulting cross-linkable XP2 exhibited the lowest dark current density of 5.81 × 10 −9 A cm −2 at −0.1 V, which is about 2 orders of magnitude lower than the control devices. A remarkable responsivity of 0.5 A W −1 and a detectivity of >1 × 10 13 Jones at a near-infrared wavelength of 800 nm were achieved. Of particular importance is that the resulting device exhibited a linear dynamic range of >135 dB associated with a high working frequency that is shorter than typical commercial digital imagers. The planar heterojunction devices demonstrate that the dark current is closely correlated to the charge generation, which relied on the highest occupied molecular orbital energy levels of the developed cross-linked interlays. The Mott−Schottky analysis revealed that the optimized cross-linked interlayer increased the depletion width of the devices.
Efficient charge transfer is closely related to improvement of the performance of quantum dot (QD)-based solar cells. In this paper, the effects of surface ligands with different alkyl chain lengths ((1-dodecanethiol (DDT) and 1-octanethiol (OT)) on the electron transfer process in InP/ZnS QDs were studied by ultrafast spectroscopy. With adsorption of the electron acceptor anthraquinone (AQ), both hot electron transfer and band-edge electron transfer between the QDs and acceptor were observed. The analysis shows that there is a more efficient (hot) electron transfer process in shorter-chain ligand OT-capped QDs compared with DDT-capped QDs, which is probably because of the improved passivation and lower density of trap states for OT-capped QDs in which electron trapping may compete with electron transfer and reduce the efficiency of electron transfer. This work enhances the understanding of how the chain length of ligands affects the electron transfer process from the perspective of ultrafast photophysical properties, and it may provide valuable insight into how to improve the performance of optoelectronic devices through surface-ligand engineering.
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