Xinhua Ouyang

Efficient polymer solar cells based on the synergy effect of a novel non-conjugated small-molecule electrolyte and polar solvent

A novel non-conjugated small-molecule electrolyte was invented as a cathode interlayer in PTB7:PC71BM-based polymer solar cells (PSCs). We discovered a significant synergy effect for improving the device efficiency between methanol treatment and the interlayer. The methanol treatment mainly contributed to the open-circuit voltage, while the interlayer primarily enhanced the short-circuit current and fill factor. Under the effective synergy effect, power conversion efficiencies (PCEs) of PTB7:PC71BM-based PSCs were largely improved from 3.89% to 9.79% for conventional PSCs and from 7.34% to 9.10% for inverted PSCs. Our findings create a new path of interfacial modification for highly efficient PSCs.

Highly efficient single- and multi-emission-layer fluorescent/phosphorescent hybrid white organic light-emitting diodes with ∼20% external quantum efficiency

A blue fluorophore of N,N-diphenyl-4′′-(1-phenyl-1H-benzo[d]imidazol-2-yl)-[1,1′:4′,1′′-terphenyl]-4-amine (BBPI) was utilized as the blue fluorescent emitter and the host of a phosphorescent emitter to fabricate highly efficient fluorescent/phosphorescent (F/P) hybrid white organic light-emitting diodes (WOLEDs) in a single- or multi-emission-layer architecture. For the single-emission-layer WOLEDs consisting of only the blue emitter BBPI and yellow complementary phosphorescent emitter PO-01 in the emission layer, a maximal current efficiency (CE) of 49.1 cd A−1, power efficiency (PE) of 52.0 lm W−1, and external quantum efficiency (EQE) of 16.3% were achieved by modulating the dopant concentration, indicating efficient singlet and triplet exciton separation and utilization ability in the emission layer. An improved EQE of 17.1%, broader spectral coverage, and higher color rendering index (CRI) were achieved by inserting a non-doped blue emission layer of BBPI and a green emission layer of CBP:Ir(PPy)3. A further improved EQE of up to 19.7% could be achieved when an orange-red phosphorescent emitter PQ2Ir was used instead of PO-01, and it is one of the best reported values for the F/P hybrid WOLEDs.

Highly-efficient hybrid white organic light-emitting diodes based on a high radiative exciton ratio deep-blue emitter with improved concentration of phosphorescent dopant

An improved concentration of phosphorescent dopant for highly-efficient hybrid white organic light-emitting diodes based on a high radiative exciton ratio (80%) deep-blue emitter has been developed. The high radiative exciton ratio for the deep-blue emitter was found to be the transfer from the higher triplet (T5) to the lowest singlet state (S1) by a “hot-exciton” process. Notably, when the concentration of Ir(2-phq)3 is up to 0.9 wt%, the OLED still exhibited white emission with a maximum total EQE, CE and PE of 22.3%, 53.7 cd A−1 and 60.2 lm W−1, respectively. The exciton transfer mechanism in a high concentration of phosphorescent dopant was also discussed. The studies provide a way to obtain high performance F/P hybrid WOLEDs with a simple architecture and improved doping concentration.

Anthradithiophene-benzothiadiazole-based small molecule donors for organic solar cells

A new A–D–A small molecule involving anthradithiophene as a donor and benzothiadiazole as an acceptor unit has been synthesized by Stille coupling reaction. Its thermal, optical and electronic properties, hole mobility and photovoltaic properties have been fully characterized. The resulting material shows a broad absorption range (300–750 nm), a low band gap (1.59 eV) and a moderate hole mobility (8.81 × 10−4 cm2 V−1 s−1). We used the new small molecule blended with PC71BM as the active layer to fabricate solution-processed organic solar cells (OSCs), and employed a variety of post-treatment methods to optimize the device performance. With the help of polar solvent exposure, the highest power conversion efficiency (PCE) of 0.55% was obtained. These results would supply useful information to understand the relationship between molecular structure and photovoltaic properties of anthradithiophene/benzothiadiazole-based OSCs.

Highly efficient polymer solar cells using a non-conjugated small-molecule zwitterion with enhancement of electron transfer and collection

A novel non-conjugated small-molecule zwitterion is developed as a cathode interfacial material to enhance the electron transfer and collection properties of high-performance PSCs. The devices show significantly increased performance with power conversion efficiencies up to 9.51%. It is noteworthy that the results here provide significant scientific insights into further improvement of interfacial modification and performance of polymer solar cells.

Comparative studies on OLED performances of chloro and fluoro substituted Zn(II) 8-hydroxyquinolinates

Two novel 8-hydroxyquinoline metallic derivatives, (E)-2-[(2,3,4,5-tetrafluorophenyl)ethenyl]-8-hydroxyquinolate zinc (5) and (E)-2-[2-(2,6-dichlorophenyl)ethenyl]-8-hydroxyquinolate zinc (6) were synthesized and characterized by 1H NMR, ESI-MS, FT-IR and elemental analysis. Photoluminescence spectra revealed that the complexes showed strong fluorescence with maximum emissions at 575 and 607 nm. Compared with that of complex 5, the fluorescence quantum yield and average fluorescence lifetime of complex 6 were efficiently reduced. The heavy atom effect of Cl and distinct molecular interactions were found to play an important role in modulating or improving the properties of the complexes. Multilayer organic light-emitting diodes (OLEDs) were fabricated using these complexes. The results show they are good candidates for yellow OLEDs with maximum luminance of 7123 cd m−2 for compound 5 and 9143 cd m−2 for compound 6, as well as luminance efficiencies of 2.26 cd A−1 and 2.60 cd A−1, respectively. As the substituents are changed from fluorine to chlorine, the organic electroluminescent device based on the complex 6 shows overall better performance than that of complex 5. The calculated HOMO–LUMO energy gaps for complexes 5 and 6 were in good agreement with the experimental results.

Multifunctional emitters for efficient simplified non-doped blueish green organic light emitting devices with extremely low efficiency roll-off

Highly efficient organic light-emitting diodes (OLEDs) with simplified device structures are widely desired for both scientific research and industrial applications. However, a very limited number of simplified OLEDs have been reported to date. In this work, two multifunctional blueish green emitters, BPTPETPAI and 2TPETPAI, are designed and synthesized. Owing to the presence of a tetraphenylethene (TPE) moiety, their aggregation induced emission (AIE) properties are also investigated. High photoluminescence efficiencies of the two compounds in non-doped films render them good emitters for non-doped devices. Multilayer non-doped devices based on these emitters achieve maximum external quantum efficiencies (EQEs) and current efficiencies (CEs) of 3.13% and 6.14 cd A−1 as well as 3.25% and 6.70 cd A−1 for BPTPETPAI and 2TPETPAI, respectively. Given their shallow highest occupied molecular orbital (HOMO) energy levels, both emitters can also be used as hole injection and hole transporting materials. Based on this, single layer devices show even higher efficiencies with extremely low efficiency roll-off, achieving maximum CEs as high as 7.12 cd A−1 and 7.80 cd A−1 using BPTPETPAI and 2TPETPAI, respectively. These results demonstrate a bright prospect for the development of highly desired multifunctional emitters as well as simplified OLEDs with significant reduction in the fabrication cost of the device.

CCDC 915957: Experimental Crystal Structure Determination

Related Article: Ying Liu, Yang Wang, Ling Ai, Zhiyang Liu, Xinhua Ouyang, Ziyi Ge|2015|Dyes Pigm.|121|363|doi:10.1016/j.dyepig.2015.05.032