Amjad Islam

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.

Non-Doped Sky-Blue OLEDs Based on Simple Structured AIE Emitters with High Efficiencies at Low Driven Voltages

Blue organic light-emitting diodes (OLEDs) are necessary for flat-panel display technologies and lighting applications. To make more energy-saving, low-cost and long-lasting OLEDs, efficient materials as well as simple structured devices are in high demand. However, a very limited number of blue OLEDs achieving high stability and color purity have been reported. Herein, three new sky-blue emitters, 1,4,5-triphenyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (TPEI), 1-(4-methoxyphenyl)-4,5-diphenyl-2-(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (TPEMeOPhI) and 1-phenyl-2,4,5-tris(4-(1,2,2-triphenylvinyl)phenyl)-1H-imidazole (3TPEI), with a combination of imidazole and tetraphenylethene groups, have been developed. High photoluminescence quantum yields are obtained for these materials. All derivatives have demonstrated aggregation-induced emission (AIE) behavior, excellent thermal stability with high decomposition and glass transition temperatures. Non-doped sky-blue OLEDs with simple structure have been fabricated employing these materials as emitters and realized high efficiencies of 2.41 % (4.92 cd A-1 , 2.70 lm W-1 ), 2.16 (4.33 cd A-1 , 2.59 lm W-1 ) and 3.13 % (6.97 cd A-1 , 4.74 lm W-1 ) for TPEI, TPEMeOPhI and 3TPEI, with small efficiency roll-off. These are among excellent results for molecules constructed from the combination of imidazole and TPE reported so far. The high performance of a 3TPEI-based device shows the promising potential of the combination of imidazole and AIEgen for synthesizing efficient electroluminescent materials for OLED devices.

Benzophenone-based small molecular cathode interlayers with various polar groups for efficient polymer solar cells

A series of novel benzophenone-based small molecular cathode interfacial materials with different polar groups including hydroxyl groups, neutral amino groups, amino N-oxide, and sulfobetaine ions were synthesized for PTB7:PC71BM-based polymer solar cells between the active layer and Al electrode. The photovoltaic properties of the devices with these interfacial materials were studied. The differences in interface modification performance of hydroxyl and amino interfacial materials were investigated for the first time. The devices with a solution-processed amino N-oxide-based interlayer showed a PCE of 9.34% with the highest short-circuit current density and fill factor by reducing the series resistance and charge recombination compared to the devices with the other interlayers in this work. The study of structure–property relationships proposes the significant guidance for the design of efficient cathode interface materials in organic solar cells.

High-Performance Polymer Solar Cells Employing Rhodamines as Cathode Interfacial Layers

The development of simple and water-/alcohol-soluble interfacial materials is crucial for the cost-effective fabrication process of polymer solar cells (PSCs). Herein, highly efficient PSCs are reported employing water-/alcohol-soluble and low-cost rhodamines as cathode interfacial layers (CILs). The results reveal that rhodamine-based CILs can reduce the work function of the Al cathode and simultaneously increase the open-circuit voltage, current density, fill factor, and power conversion efficiency (PCE) of PSCs. The solution-processed rhodamine-based PSCs demonstrated a remarkable PCE of 10.39%, which is one of the best efficiencies reported for thieno[3,4-b]thiophene/benzodithiophene:[6,6]-phenyl C71-butyric acid methyl ester-based PSCs so far. The efficiency is also 42.3% higher than that of the vacuum-deposited Ca-based device (PCE of 7.30%) and 21.5% higher than that of the complicated solution-processable polymeric electrolyte poly[(9,9-bis(3-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)]-based device (PCE of 8.55%). Notably, rhodamines are very economical and have been extensively used as dyes in industries. Our work indicates that rhodamines have shown a strong potential as CILs compared to their counterparts in the large-area fabrication process of PSCs.

Furan-containing conjugated polymers for organic solar cells

Development of organic semiconductors is one of the most intriguing and productive topics in material science and engineering. Many efforts have been made on the synthesis of aromatic building blocks such as benzene, thiophene and pyrrole due to the facile preparation accompanied by the intrinsic environmental stability and relatively efficient properties of the resulting polymers. In the past, furan has been less explored in this field because of its high oxidation potential. Recently, furan has attracted obsession due to its weaker aromaticity, the greater solubilities of furan-containing π-conjugated polymers relative to other benzenoid systems and the accessibility of furan-based starting materials from renewable resources. This review elaborates the advancements of organic photovoltaic polymers containing furan building blocks. The uniqueness and advantages of furan-containing building blocks in semiconducting materials are also discussed.

Enhanced high-open circuit voltage in fluorinated benzoselenadiazole-based polymer solar cells

Three new donor–acceptor copolymers (PCDTBSe, PCDTFBSe, and PCDTDFBSe) were designed and synthesized with 2,7-carbazole as the donor (D) unit and benzoselenadiazole (BSe), monofluoro-benzoselenadiazole, and difluoro-benzoselenadiazole as the acceptor (A) units, respectively. The structure–property relationship of these polymers was elucidated in bulk heterojunction polymer solar cells. All the polymers were fully characterized and exhibited good thermal stability and broad absorption. The highest occupied molecular orbitals (HOMOs) of the PCDTBSe (−5.29 eV), PCDTFBSe (−5.32 eV), and PCDTDFBSe (−5.35 eV) were decreased by incorporating fluorine atoms on the polymer backbone. The low-lying HOMO energy level suggested that the polymers would exhibit high open circuit voltage (V OC) when blended with fullerene as the electron acceptor. Solar cell based on PCDTFBSe displayed a power conversion efficiency of 1.09% with a short-circuit current density (JSC) of 4.29 mA cm−2, a VOC of 0.78 V, and a fill factor (FF) of 32.51%, under the illumination of AM1.5G, 100 mW cm−2.

Research Progress and Manufacturing Techniques for Large-Area Polymer Solar Cells

For organic photovoltaic (OPV) to ensure the best technology that can gain credibility among other existing solar cells, large-area devices must be prepared and shared widely to gain harmony on performance, such as operational stability and power conversion efficiency (PCE). Progress in large-area polymer solar cells is mainly addressed in context of the processing techniques leading to the fabrication of complete devices. In this contribution, we review the techniques of film formation such as spin coating, screen printing, inkjet printing, doctor blading, and roll-to-toll. In addition, the structure, operational principles, and characteristics of OPV are described as well.