Search

The hole and electron mobilities of the amorphous films of the organic semiconductor 4,4′- N, N′-dicarbazole-biphenyl (CBP) at different electric fields were measured through the time of flight (TOF) method. Based on its crystalline structure, the hole and electron mobilities of CBP were calculated. A detailed comparison between experimental and theoretical results is necessary for further understanding its charge transport properties. In order to do this, charge mobilities at zero electric field, μ(0), were deduced from experimental data as a link between experimental and theoretical data. It was found that the electron transport of CBP is less affected by traps compared with its hole transport. This unusual phenomenon can be understood through the distributions of frontier molecular orbitals. We showed that designing materials with frontier molecular orbitals localized at the center of the molecule has the potency to reduce the influence of traps on charge transport and provide new insights into designing high mobility charge transport materials. [ABSTRACT FROM AUTHOR]

In this letter, the authors investigated the photostability of pentacene organic thin film transistors (OTFTs) with Ta2O5 gate insulators. Under illumination, the threshold voltage shift of the Ta2O5-based OTFTs reached 5.51 V. The obvious photoinstability was attributed to the electron trapping ability of the Ta2O5 film. To solve this problem, poly(4-vinylphenol) (PVP), a type of polymer with low trap density and high photostability was used to modify Ta2O5. It was found that OTFTs with Ta2O5/PVP double gate insulators showed improved performance, and the voltage shift after illumination was greatly reduced to 0.04 V. [ABSTRACT FROM AUTHOR]

Electron transport layer (ETL) is a functional layer of great significance for boosting the power conversion efficiency (PCE) of perovskite solar cells (PSCs). To date, it is still a challenge to simultaneously reduce the surface defects and improve the crystallinity in ETLs during their low‐temperature processing. Here, a novel strategy for the mediation of in situ regrowth of SnO2 nanocrystal ETLs is reported: introduction of controlled trace amounts of surface absorbed water on the fluorinated tin oxide (FTO) or indium–tin oxide (ITO) surfaces of the substrates using ultraviolet ozone (UVO) pretreatment. The optimum amount of adsorbed water plays a key role in balancing the hydrolysis–condensation reactions during the structural evolution of SnO2 thin films. This new approach results in a full‐coverage SnO2 ETL with a desirable morphology and crystallinity for superior optical and electrical properties, as compared to the control SnO2 ETL without the UVO pretreatment. Finally, the rigid and flexible PSC devices based on the new SnO2 ETLs yield high PCEs of up to 20.5% and 17.5%, respectively. [ABSTRACT FROM AUTHOR]

Here, a simple and generally applicable method of fabricating efficient and stable Pb‐Sn binary perovskite solar cells (PVSCs) based on a galvanic displacement reaction (GDR) is demonstrated. Different from the commonly used conventional approaches to form perovskite precursor solutions by mixing metal halides and organic halides such as PbI2, SnI2, MAI, FAI, etc., together, the precursor solutions are formulated by reacting pure Pb‐based perovskite precursor solutions with fine Sn metal powders. After the ratios between Pb and Sn are optimized, high PCEs of 15.85% and 18.21% can be achieved for MAPb0.4Sn0.6I3 and (FAPb0.6Sn0.4I3)0.85(MAPb0.6Sn0.4Br3)0.15 based PVSCs, which are the highest PCEs among all values reported to date for Pb‐Sn binary PVSCs. Moreover, the GDR perovskite‐based PVSCs exhibit significantly improved ambient and thermal stability with encapsulation, which can retain more than 90% of their initial PCEs after being stored in ambient (relative humidity (RH) ≈50%) for 1000 h or being thermal annealed at 80 °C for more than 120 h in ambient conditions. These results demonstrate the advantage of using GDR to prepare tunable bandgap binary perovskites for devices with greatly improved performance and stability. A simple and generally applicable method to fabricate efficient and stable Pb‐Sn binary perovskite solar cells (PVSCs) based on a galvanic displacement reaction (GDR) is demonstrated. With optimizing the ratio of Pb and Sn, high PCEs of 15.85% and 18.21% are achieved for Pb‐Sn binary based PVSCs. Moreover, these Pb‐Sn based PVSCs exhibit improved stability with encapsulation. [ABSTRACT FROM AUTHOR]

Abstract: Efficient single emitting layer electrophosphorescent white organic light-emitting diodes (WOLEDs) based on small molecules were fabricated by solution process. A solution processible wide-gap compound 9,9-bis[4-(3,6-di-tert-butylcarbazol-9-yl)phenyl] fluorene (TBCPF) was used as the host material and 1,3-bis[(4-tert-butylphenyl)-1,3,4-oxidiazolyl]phenylene (OXD-7) was doped to enhance the electron transport in the emission layer. The optimized single active layer WOLED with three phosphorescent dopants showed a maximum luminance efficiency of 20.8cd A−1 and a maximum luminance of 26,600cdm−2. And the maximum efficiency of double-layer WOLEDs with an additional hole-blocking/electron-transporting layer was further improved to 29.6cd A−1. The color of the devices shifted slightly with the bias voltage. The energy transfer processes and the origin of the white emission in the single emitting layer were also discussed based on the measurement of the transient photoluminescence. [Copyright &y& Elsevier]

Abstract: A series of zinc complexes with salicylidene–aniline and its derivatives as ligands have been designed and synthesized for electron transport in organic light-emitting diodes (OLEDs). A systematic study on their thermal, photophysical, electrochemical and electron transport properties has been carried out and demonstrated that the substitution of −CH3, −OCH3, −CN and −N(CH3)2 on aniline ring of ligands can finely tune the properties of the corresponding zinc complexes. The density functional theory calculations of location and distribution of the frontier molecular orbital states unveiled the relationships between the substituents and the photophysical and electrochemical properties of these complexes. OLEDs with bis(salicylidene-p-methylaniline)zinc(II) (Zn(sama)2) as the electron transport layer exhibited high current efficiency, indicating its great potential as a useful electron transport material for OLEDs. [Copyright &y& Elsevier]

• A simple and low-cost non-toxic RbF modifier is introduced for the first time in the ETL-free PSCs. • A superior efficiency of 18.79% along with a reduced J-V hysteresis in the ETL-free PSCs is achieved. • The barrier-free FTO/perovskite contact favors efficient electron transfer and suppresses the carrier recombination. The development of highly efficient electron transport layer free perovskite solar cells (ETL-free PSCs) with simplified and economical device configurations can significantly motivate the commercialization of PSCs. However, the performance of ETL-free PSCs has been hampered by the sluggish charge extraction and severe charge carrier recombination due to the energy-level mismatch at the interface of the perovskite and the transparent conductive electrode FTO (fluorine doped tin-oxide). In this study, this issue is well solved by modifying the FTO surface with a simple, low-cost and non-toxic rubidium fluoride (RbF) interlayer. An interfacial dipole layer is formed on the FTO surface by inserting a RbF layer, which tunes the work function of FTO, eliminates the electron transport barrier and optimizes the energy-level alignment at the FTO/perovskite interface, thereby enhancing the charge transfer and suppressing the carrier recombination. Consequently, the rigid ETL-free PSCs with RbF layer yield high efficiencies of up to 18.79%, higher than that of ETL-free devices on bare FTO (16.03%). By virtue of the low-temperature processability, a superior PCE of 15.7% has been achieved by flexible ETL-free PSCs fabricated on RbF modified plastic substrate. This study provides a simple, efficient and environmentally friendly approach to modify the FTO electrode for fabricating ETL-free PSCs, which contribute to promote the design of advanced interface materials for simplified and high-performance perovskite photovoltaics. [ABSTRACT FROM AUTHOR]