Shi-Jian Su

Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in polymer solar cells

Simultaneous enhancement of open-circuit voltage, short-circuit current density, and fill factor in highly efficient polymer solar cells by incorporating an alcohol/water-soluble conjugated polymer as cathode interlayer is domonstrated. When combined with a low-bandgap polymer PTB7 as the electron donor material, the power efficiency of the devices is improved to a certified 8.370%. Due to the drastic improvement in efficiency and easy utilization, this method opens new opportunities for PSCs from various material systems to improve towards 10% efficiency.

Ultra High Efficiency Green Organic Light-Emitting Devices

We developed ultra high efficiency green organic light-emitting devices (OLEDs) using a novel electron transport material containing dipyridylphenyl moieties and green phosphorescent emitter, fac tris(2-phenylpyridine)iridium, Ir(ppy)3. An OLED with a simple structure of glass/indium–tin oxide/polymer buffer layer/arylamine derivative as a hole transport layer/Ir(ppy)3-doped dicarbazolylbiphenyl as an emitter layer/dipyridylphenyl derivative as an electron transport layer/LiF/Al exhibited low drive voltages, which were 2.5 V at 100 cd/m2 and 2.9 V at 1000 cd/m2. High external quantum efficiencies of 29% at 100 cd/m2 and 26% at 1000 cd/m2 were also observed, which lead to the ultra high power efficiencies of 133 lm/W at 100 cd/m2 and 107 lm/W at 1000 cd/m2.

Solution-processed bulk heterojunction solar cells based on a porphyrin small molecule with 7% power conversion efficiency

A porphyrin small molecule with less bulky substituents at the porphyrin periphery has been synthesized as a donor material, which exhibits a power conversion efficiency of up to 7.23% under AM 1.5 G irradiation (100 mW cm−2) for the solution-processed bulk heterojunction solar cells with PC61BM as the acceptor material.

Tuning Energy Levels of Electron-Transport Materials by Nitrogen Orientation for Electrophosphorescent Devices with an ‘Ideal’ Operating Voltage

In the last two decades, many studies have focused on improving external electroluminescence effi ciency ( η ext ) of organic lightemitting devices (OLEDs). [ 1 ] Lowering operating voltages is also crucially important to improve their power conversion effi ciency especially for high power-effi ciency applications such as in mobile devices. [ 2 ] OLEDs with p-doped hole-transport layers (HTLs) and n-doped electron-transport layers (ETLs), called p-i-n OLEDs, have been developed as low-voltage effi cient lighting sources. [ 3 ] However, a hole/exciton-block buffer layer is crucially important to prevent exciton quenching in the emissive layer (EML) by the alkaline metal dopants in the ETL, and insertion of the hole/exciton-block buffer layer and usage of n -doped ETL may induce more complexity of device structure and thus higher cost. In addition, the approach of using alkaline metals might be hampered by stability issues and leads to manufacturing diffi culties. We report here on a series of 1,3,5-triazine-core-containing electron-transport materials (ETMs) as an undoped ETL, whose energy levels can be tuned by introducing pyridine rings on the periphery of the molecule and also orientation of nitrogen. An unprecedented low operating voltage of 2.42 V, corresponding to the emitting photon energy ( hv ), was achieved for the fac -tris(2-phenylpyridine) iridium (Ir(PPy) 3 ) based green phosphorescent OLEDs at 100 cd m − 2 without consumption of their effi ciency. Moreover, the threshold voltage for electroluminescence can be even 0.1 ∼ 0.2 V lower than the minimum value of hv /e. As an ETM that can act as an ETL as well as a hole/excitonblock layer, it should posses a low-lying lowest unoccupied molecular orbital (LUMO) energy level to give a low electron injection barrier, a low-lying highest occupied molecular orbital (HOMO) energy level to block hole leakage from EML, and a

Novel Four-Pyridylbenzene-Armed Biphenyls as Electron-Transport Materials for Phosphorescent OLEDs

A series of four-pyridylbenzene-armed biphenyl derivatives were designed and synthesized as an electron-transport and exciton- and hole-block layer for the fac-tris(2-phenylpyridine)iridium (Ir(PPy)3)-based green phosphorescent organic light-emitting devices (OLEDs), giving improved efficiency in comparison to that with both the electron-transport layer of tris(8-hydroxyquinoline)aluminum (Alq3) and the exciton- and hole-block layer of 2,9-dimethyl-4,7-diphenylphenathroline (BCP).

A Series of New Medium‐Bandgap Conjugated Polymers Based on Naphtho[1,2‐c:5,6‐c]bis(2‐octyl‐[1,2,3]triazole) for High‐Performance Polymer Solar Cells

A series of novel conjugated copolymers based on naphtho[1,2-c:5,6-c]bis(2-octyl-[1,2,3]triazole) (TZNT) are synthesized. These copolymers exhibit medium bandgaps of ≈1.9 eV. One of them demonstrates a high performance of up to 6.10% power conversion efficiency in a bulk-heterojunction (BHJ) solar-cell device. The performance can be further enhanced to 7.11% when applied in an inverted device architecture, using PF3 N-OX as an interfacial modifier.

Three-carbazole-armed host materials with various cores for RGB phosphorescent organic light-emitting diodes

A series of three-carbazole-armed host materials containing various arylene cores, like benzene (1,3,5-tris(3-(carbazol-9-yl)phenyl)-benzene, TCPB), pyridine (2,4,6-tris(3-(carbazol-9-yl)phenyl)-pyridine, TCPY), and pyrimidine (2,4,6-tris(3-(carbazol-9-yl)phenyl)-pyrimidine, TCPM), were developed for red, green, and blue phosphorescent organic light-emitting diodes (OLEDs). An intramolecular charge transfer was observed for TCPY and TCPM with heterocyclic cores of pyridine and pyrimidine, giving bathochromic shifts in the photoluminescent spectrum and reduced energy band gaps in comparison with TCPB with a benzene core. In addition, lower energy singlet and triplet excited states, reduced lowest unoccupied molecular orbital (LUMO) energy level, smaller singlet–triplet exchange energy (ΔEST), and improved bipolarity were also achieved with introducing heterocycles of pyridine and pyrimidine instead of benzene. In contrast to the slightly decreased triplet energy (ET), a significantly decreased ΔEST was achieved by introducing heterocycles of pyridine and pyrimidine as the core, and the more nitrogen atoms in the central heterocycle, the smaller ΔEST is achieved. Reduced driving voltages were achieved for the green and red phosphorescent OLEDs by utilizing TCPY and TCPM as the host due to their decreased ΔEST and lower-lying LUMO energy level, proving that more carriers must be injected into the emitting layer through the host molecules rather than direct carrier trapping by the dopant. Moreover, improved efficiency and suppressed efficiency roll-off were also achieved for the green and red phosphorescent OLEDs based on TCPY and TCPM due to their improved bipolarity and thus improved carrier balance.

Nitrogen heterocycle-containing materials for highly efficient phosphorescent OLEDs with low operating voltage

Since their discovery, phosphorescent organic light-emitting diodes (PHOLEDs) have been developed for more than ten years. To improve the electricity-to-light conversion efficiency of PHOLEDs, it is of great importance to improve their external quantum efficiency and to decrease their operating voltage. The improvement of functional materials such as host materials and carrier transport materials, especially electron transport materials, plays the most important role in reaching these targets. In this feature article, we provide a brief review of the recent developments in nitrogen heterocycle-containing functional materials for PHOLEDs. Special attention is paid to the issue of how to utilise the molecular design strategy in achieving the development of high-performance host and electron transport materials and of how to use these nitrogen heterocycle-containing materials to create PHOLEDs with efficiencies and operating voltages that reach the theoretical limits.

Fluorescent Organic Planar pn Heterojunction Light‐Emitting Diodes with Simplified Structure, Extremely Low Driving Voltage, and High Efficiency

Fluorescent organic light-emitting diodes capable of radiative utilization of both singlet and triplet excitons are achieved via a simple double-layer planar pn hetero-junction configuration without a conventional emission layer, leading to high external quantum efficiency above 10% and extremely low driving voltages close to the theoretical minima.

High-Efficiency WOLEDs with High Color-Rendering Index based on a Chromaticity-Adjustable Yellow Thermally Activated Delayed Fluorescence Emitter.

A chromaticity-adjustable yellow thermally activated delayed fluorescence (TADF) material, PXZDSO2 as a triplet harvester provides a rational device concept, giving two-color and three-color pure organic white organic light-emitting diodes (WOLEDs) with unprecedented color-rendering index of 95 and external quantum efficiency of 19.2%.