Jiadong Zhou

An electrochemically deposited film as an interface layer to improve the performance of polymer light-emitting diodes

An insoluble electrochemically cross-linked thin film is successfully applied as an interface layer between PEDOT:PSS and the light emitting layer in solution-processed polymer light-emitting diodes for enhanced device performance.

The effect of interfacial diffusion on device performance of polymer solar cells: a quantitative view by active-layer doping

The diffusion of constituent materials at interfaces is one of the key factors for device performance and stability. In this work, the effect of interfacial diffusion of a classic interfacial material PFN on device performance of polymer solar cells was studied quantitatively by doping PFN into active layer based on P3HT:PC61BM blend. The PCEs of devices with 550 ppm PFN decrease to half compared to those of the control devices without PFN, which are mainly attributed to the decrease of short-circuit current (Jsc) and fill factor (FF). Advanced analyses of equivalent circuit, absorption spectra, and atomic force microscopy indicates that the presence of PFN in the active layer increases the leakage current, decreases the aggregation of P3HT, and reduces the phase separation. This research reveals the physical mechanism of interfacial diffusion in device performance and provides a basis for further improving the performance and stability of PSCs.

Preparation and electronic characteristics of anionic perylene bisimide films

Neutral perylene bisimides (PBI) are well-known n-type organic semiconductors, with number of challenging electronic properties in their neutral and reduced states. We report the characteristic electronic properties of PBI anionic films. We unexpectedly discovered that pristine PBI dianion film showed p-type character, while oxidized dianion film (dominant neutral state with few radical anions) showed normal n-type semiconductor character based on Seebeck effect measurements. Both kinds of films exhibit high electrical conductivity with a potential for thermoelectric applications. The mechanism of polarity reversal is proposed.

Pyridal[2,1,3]thiadiazole as strong electron-withdrawing and less sterically-hindered acceptor for highly efficient donor–acceptor type NIR materials

Pyridal[2,1,3]thiadiazole (PT) is an analogue of benzo[1,2,5]thiadiazole (BT), which is a common acceptor in charge transfer (CT) chromophores. Compared with BT, PT is more electron-deficient and less sterically hindered. Herein we demonstrate the effect of using PT as proto-acceptor in the design of D–A type NIR emitting materials. The compound p-TPA-PT-CN was synthesized, which combines PT with the donor triphenylamine (TPA) and cyano-substituent (CN), and shows NIR emission at ∼700 nm with a high PL efficiency of 0.3 in both solution and solid state. The strong D–A interaction within p-TPA-PT-CN results in a low energy charge-transfer state. The pyridine nitrogen of PT reduces the steric hindrance between PT and the adjacent TPA donor segment, resulting in increased planarity and strong mixing (hybridization) of CT and π–π states (HLCT). Such strong mixing contributes towards a higher luminous efficiency. The OLEDs fabricated with p-TPA-PT-CN as the emitting layer exhibited an EQE of 1.47% and Lmax = 640 cd m−2, which are amongst the highest values reported for NIR-OLED devices.

Conjugated ionic state and its distribution in perylene bisimide doped film: A characterization of Z -scanning in confocal Raman spectroscopy

Ion-doped states are significant for improving the performance in organic semiconductor-based devices, which require clear characterization to understand their relationship with conductivity and charge transporting mechanisms. In this paper, Raman spectroscopy is used to track the evolution of a dianion-anion-neutral mixture in a perylene bisimide (PBI)-doped film under air, with z-scanning carried out in the confocal mode. The precise distribution for the different states along the film depth is realized within 3.5 μm. The whole film is clearly divided into three regions: the ion-poor state, transition region and ion-rich state. The ion ratio and distribution are strongly related to the film conductivity and the onset voltage shift. Changes in the distribution of the ionic species during oxidation and electrode catalysis are clearly recorded by z-scanning, which is beneficial for understanding the charge transfer properties as well as the mechanism underlying working devices.

Chlorine Atoms Induced Molecular Interlocked Network in a Non-Fullerene Acceptor

The differences between the introduction of chlorine and fluorine atoms to small-molecule acceptors were deeply investigated. From the single-crystal structures of three molecules, the Cl-substitution intervention into the molecular configuration and packing mainly lies in three aspects as follows: single molecule configuration, one direction of the intermolecular arrangement, and three-dimensional (3D) molecular packing. First, the introduction of the chlorine atom in IDIC-4Cl leads to a more planar molecular configuration than IDIC-4H and IDIC-4F because of the formation of a molecular interlocked network induced by the strong Cl···S intermolecular interactions. Second, IDIC-4Cl shows the closest π-π stacking distance and the smallest dihedral angle (0°) between adjacent molecules to form ideal J-aggregation, which should be beneficial for charge transportation between different connected molecules in this direction. Finally, the interlocked interactions between Cl and S atoms lead to a highly ordered 3D molecular packing, in which the end groups will form an ideal overlapped packing among different molecules, whereas the other two analogues with H or F show less ordered packing of their 1,1-dicyanomethylene-3-indanone ending groups. Organic solar cells based on IDIC-4Cl show the highest power conversion efficiency (PCE) of 9.24%, whereas the PCEs of IDIC-4H- and IDIC-4F-based devices are 4.57 and 7.10%, respectively.