Highly efficient green and orange-red PhOLEDs with low efficiency roll-off enabled by a bipolar violet-blue phenanthroimidazole-based fluorophore.

Organic solar cells (OSCs) have attracted wide attention due to their economy, environmental protection, and potential for large-scale commercial production. The layer-by-layer (LbL) solution processing method, where donor solution and acceptor solution are coated sequentially, is a simple and effective way to fabricate OSCs, achieving a high power conversion efficiency (PCE) of up to 17%. Compared with bulk-heterojunction (BHJ) OSCs, LbL solution-processed OSCs separately adjust different layers, making the components distribute ideally in the vertical direction that is beneficial for exciton dissociation, charge transport, and charge collection. Moreover, the LbL approach has better potential in the preparation of large-area devices, which is a key link in the commercialization of OSCs. Herein, the basic principles and the latest research progress of LbL solution-processed OSCs are summarized, and the existing challenges and prospects of the LbL solution processing method in industrial production are discussed.

Efficient solution-processed exciplex OLEDs were developed by incorporating a novel small molecule electron-donor and utilizing the strategy of ternary exciplexes.

For comprehensive development of organic solar cells (OSCs), some factors such as environmental stability, low cost, insensitive film thickness, component contents tolerance, and green preparation processes are equally crucial to achieve high power conversion efficiencies (PCEs). In this work, a small molecule 3-(diethylamino)-7-imino-7H-benzo[4,5]imidazo[1,2-a]chromeno[3,2-c]pyridine-6-carbonitrile (DIBC), which is commercially available at low cost, is utilized to realize high-performance ternary OSCs. Demonstrated via Fourier transform infrared and 2D-1 HNMR, DIBC can form hydrogen bond interactions with [6,6]-phenyl-C 71 -butyric acid methyl ester (PC 71 BM) in solid films. Further electrostatic potential (ESP) calculations indicate that the hydrogen bond interaction enhances the ESP of PC 71 BM and accelerates charge transport between donor and acceptor. As a result, poly(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl) benzo[1,2-b;4,5-b0]dithiophene-2,6diylalt-(4-(2-ethylhexyl)-3-fluorothieno[3,4-b]thiophene-)-2-carboxylate-2-6-diyl(PTB7-Th):DIBC:PC 71 BM-based ternary OSC achieves a maximum efficiency of 12.17%, which is the best result of green solvent processed fullerene OSCs at present. It is noteworthy that the ternary OSCs also show great tolerance to film thickness and blend ratios. These unique properties are attributed to the hydrogen-bond-linked DIBC and PC 71 BM, which modulates molecule distribution and improves film morphology with an interpenetrating network structure. Furthermore, the DIBC containing device also exhibits good thermal and light radiation stability. These results illustrate that intermolecular hydrogen bond interaction has great potential for realizing high-performance OSCs.

Three deep-blue emitters PPi-Pid, PPi-Xid, and PPi-Mid based on a novel conjugated system phenantroimidazole-π-indolizine have been designed and synthesized. Here, indolizine with appropriate π-conjugation length was used as the acceptor profited from its high-photoluminescence quantum yield and good electron-withdrawing ability. Fluorescent organic light-emitting diodes (OLEDs) based on PPi-Pid, PPi-Xid, and PPi-Mid achieved deep-blue emissions with the Commission Internationale de L'Eclairage coordinates of (0.151, 0.076), (0.155, 0.052), and (0.153, 0.052); high brightness of 14350, 4377, and 4002 cd/m; and high external quantum efficiencies (EQEs) of 6.01, 3.90, and 4.28%, respectively. Moreover, it is noticeable that all of the devices exhibited efficiencies increasing with brightness. In particular, the PPi-Pid-based device exhibited high EQE over 6% at a high brightness of 14350 cd/m. Such high brightness along with high EQE is very rare whether in deep-blue fluorescent or thermally activated delayed fluorescent OLEDs.

Blue and white solution-processed OLEDs with low driving voltages, over 20% maximum external quantum efficiency and moderate efficiency decrease were realized by using interfacial exciplex hosts.

Deep blue emitters with high quantum yield, good stability, and multifunctionality are still the key technology for white organic light‐emitting diodes (WOLEDs). To address this, two multifunctional deep‐blue materials 4‐{2‐[4′‐(1,4,5‐triphenyl‐4,5‐dihydro‐1H‐imidazol‐2‐yl)‐biphenyl‐4‐yl]‐3a,11b‐dihydro‐phenanthro[9,10‐d]imidazol‐1‐yl}‐benzonitrile (CPD) and 4‐(2‐{4′‐[1‐(4‐tert‐butyl‐phenyl)‐4,5‐diphenyl‐4,5‐dihydro‐1H‐imidazol‐2‐yl]‐biphenyl‐4‐yl}‐3a,11b‐dihydro‐phenanthro[9,10‐d]imidazol‐1‐yl)‐benzonitrile (tCPD) based on phenanthroimidazole units are designed, synthesized, and characterized. Both the materials show high quantum yields and good stabilities. The deep‐blue fluorescent devices using CPD and tCPD as emitters show maximum external quantum efficiency (EQE) of 5.80% and 4.71% along with Commission Internationale de I'Eclairage (CIE) coordinates of (0.15, 0.07) and (0.15, 0.09), respectively. Two‐color based WOLEDs are demonstrated by doping Ir(MDQ)2acac into CPD and tCPD with a low doping concentration, both devices show high EQEs of 16.4% and 16.6% and CIEs of (0.49, 0.34) and (0.48, 0.32), respectively. Furthermore, three‐color based fluorescence/phosphorescence‐WOLEDs (F/P‐WOLEDs), with reasonable exciton management, are fabricated to enhance exciton utilization and improve device performance. CPD‐based WOLED shows high efficiencies of 49.4 cd A−1, 53.5 lm W−1, 19.0%, and CIE coordinate of (0.46, 0.46). With the same structure, tCPD‐based device also shows high efficiencies of 40.6 cd A−1, 47.2 lm W−1, 19.4% along with CIE coordinate of (0.43, 0.45). These results are among the best of reported deep‐blue OLEDs and F/P‐WOLEDs.

High performance green phosphorescent OLEDs using novel bromine-substituted compounds as hole transport layers were fabricated.