Effective Electron Transport Layer Research Articles

Improved characteristics of polymer light-emitting diode based on poly(alkylfluorene) with functional layer fabricated by contact printing method

In the organic light-emitting diode, the multilayer structure is useful to achieve the effective carrier injection and transport, and improve the emission efficiency. The characteristics of the polymer light-emitting device with a functional layer by contact printing method are investigated. Hole transport material, the guest and electron transport material are mixed at each layer with the same host. Poly (9,9-dioctylfluorene) (F8) and Tris[1-phenylisoquinolinato-C2,N]iridium(III) (Ir(piq)3) are used as the host and guest materials. We focused on the effects of a functional layer with 1,3,5-Tris (1-phenyl-1H-benzimidazol-2-yl)benzene(TPBi) as the electron transport material doped in F8. For a non-heterostructure device with F8:TPBi functional layer, electrons are injected from the cathode interface to TPBi and transported through F8. TPBi acts as the effective hole blocking and electron transport layer as TPBi is mixed in F8 at the cathode side. Non-heterostructure device exhibits improved emission efficiency and lower driving voltage.

Effects of ytterbium on electrical and optical properties of BCP/Ag/WO3 transparent electrode based organic photovoltaic cells

This study introduces dielectric/metal/dielectric multilayers based on a WO3/Ag/WO3 (WAW) anode and Yb/BCP/Ag/WO3 (Yb/BAW) cathode for use in organic photovoltaic cells (OPVs). Here, the Yb/BCP hybrid multilayer provides an effective electron transport layer (ETL), while the Yb doping ensures that voltage loss due to interfacial band bending is effectively suppressed. Transparent OPVs produced with a structure of WAW/P3HT:PCBM/Yb/BAW are shown to exhibit a power conversion efficiency (PCE) of up to 2.42%, achieving a 65.4% fill factor (FF) under one sun irradiation. These results indicate that the use of Yb in transparent OPVs is vastly superior to other ETLs, as it improves the majority of critical parameters such as short circuit current (Jsc), fill factor (FF) and PCE. This is attributed to a decrease in the series resistance and increase in the shunt resistance, while an increase in electron mobility also helps to ensure faster sweep out.

Solution‐Processable Ultrathin Black Phosphorus as an Effective Electron Transport Layer in Organic Photovoltaics

2D van der Waals crystals, possessing excellent electronic and physical properties, have been intriguing building blocks for organic optoelectronic devices. Most of the 2D materials are served as hole transport layers in organic devices. Here,it is reported that solution exfoliated few layers black phosphorus (BP) can be served as an effective electron transport layer (ETL) in organic photovoltaics (OPVs) for the first time. The power conversion efficiencies (PCEs) of the BP‐incorporated OPVs can be improved to 8.18% in average with the relative enhancement of 11%. The incorporation of BP flakes with the optimum thickness of ≈10 nm can form cascaded band structure in OPVs, which can facilitate electron transport and enhance the PCEs of the devices. This study opens an avenue in using solution exfoliated BP as a highly efficient ETL for organic optoelectronics.

Simple solution-processed titanium oxide electron transport layer for efficient inverted polymer solar cells

Titanium oxide (TiOX) is an effective electron transport layer (ETL) in polymer solar cells (PSCs). We report efficient inverted PSCs with a simple solution-processed amorphous TiOX (s-TiOX) film as an ETL. The s-TiOX film with high light transmittance was prepared by spin-coating titanium (IV) isopropoxide isopropanol solution on indium tin oxide coated glass in inert and then placed in air under room temperature for 60min. The introduction of s-TiOX ETL greatly improved the short circuit current density of the devices. PSCs based on poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester and poly(4,8-bis-alkyloxy-benzo[1,2-b:4,5-b′]dithiophene-alt-alkylcarbonyl-thieno[3,4-b]thiophene):[6,6]-phenyl- C71-butyric acid methyl ester using s-TiOX film as ETL shows high power conversion efficiency of 4.29% and 6.7% under the illumination of AM 1.5G, 100mW/cm2, which shows enhancements compared to the conventional PSCs with poly(styrenesulfonate)-doped poly(ethylenedioxythiophene) as anode buffer layer. In addition, the device exhibits good stability in a humid ambient atmosphere without capsulation. The results indicate that the annealing-free, simple solution processed s-TiOX film is an efficient ETL for high-performance PSCs.

Facile preparation of TiOXfilm as an interface material for efficient inverted polymer solar cells

Titanium oxide (TiOX) is an effective electron transport layer in polymer solar cells (PSCs). Here, we report an efficient inverted polymer solar cell based on P3HT and fullerenes using a high density, single-step solution processed amorphous TiOX (α-TiOX) film as an electron transport layer. The α-TiOX film was prepared by spin coating tetrabutyl titanate (TBT) isopropanol solution onto ITO coated glass in a glovebox filled with N2 and then annealing at different temperatures in air. The films with high light transmittance are very smooth. The PSCs with the α-TiOX electron transport layer showed enhanced photovoltaic performance in comparison with the device using PEDOT:PSS as the anode buffer layer. The optimized power conversion efficiency (PCE) of the PSCs based on P3HT/PC61BM and P3HT/PC71BM with the α-TiOX electron transport layer reached 4.25% and 4.65%, respectively, under AM1.5G illumination (100 mW cm−2). In addition, the PSCs with the α-TiOX electron transport layer exhibited good stability. The results indicate that facile preparation of α-TiOX films using cheap TBT is promising for high-efficiency PSCs and large-scale fabrication of flexible electronics.

The investigation of the diffusion length of cathode materials in organic light emitting devices through impedance characteristics

A non-destructive method to measure the diffusion length of the cathode materials into the organic layers in organic light emitting diodes (OLEDs) is demonstrated. The measurement is based on a correlation between the transition voltage in the impedance-voltage (Z-V) characteristics, the density of the accumulation charges, and the thickness of the electron transport layers (ETLs). The transition voltages in Z-V characteristics deviate from the theoretical values owing to the decrease of the effective ETL thickness caused by the diffusion of the cathode materials, which can be used to measure the diffusion length of metal ions into organic layers in OLEDs.

Low-temperature growth and characterization of ZnO thin films for flexible inverted organic solar cells

Flexible inverted organic solar cells (IOSCs) with a zinc oxide (ZnO) thin film layer acting as an effective electron transport layer and a low reflective light absorber were fabricated in this study. The high quality ZnO thin films on flexible indium tin oxide-coated polyethersulfone (PES) substrates were grown in a non-vacuum process using mist pyrolysis chemical vapor deposition at a low temperature of 180 °C without any thermal damage to the PES substrate. The power conversion efficiency of the flexible IOSCs with ZnO thin films averaged 3.1% at a simulated air-mass of 1.5 global full-sun (100 mW cm−2) illumination, which was greater than that of flexible IOSCs with a ZnO thin film formed using a sol–gel method (approximately 2.3%).

Cobaltocene-Doped Viologen as Functional Components in Organic Electronics

Given the energy level alignment between viologen and cobaltocene, cobaltocene readily transfers electrons to the intrinsically insulating viologen, resulting in the formation of an electron transfer complex with high electron density. When cobaltocene−viologen is incorporated as active layers in organic thin-film transistors, the output current of devices scales with increasing cobaltocene concentrations. We further demonstrate that cobaltocene−viologen makes effective electron transport layers in inverted polymer solar cells.