Chunpeng Yang

White light from polymer light-emitting diodes: Utilization of fluorenone defects and exciplex

A white light polymer light-emitting diode was demonstrated with a double layer configuration: poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) blended with poly(N-vinylcarbazole) as both hole-transporting layer and electron-blocking layer, blue-emissive poly(9,9-dihexylfluorene-alt-co-2,5-dioctyloxy-para-phenylene) (PDHFDOOP) blended with green-emissive poly[6,6′-bi-(9,9′-dihexylfluorene)-co-(9,9′-dihexylfluorene-3-thiophene-5′-yl)] as an emissive layer. By annealing the emissive layer at a relatively high temperature, fluorenone defects were generated into PDHFDOOP, which formed an exciplex with poly-TPD, as a red emitter. The devices exhibit a maximum brightness of ∼4800cd∕m2 and a maximum luminous efficiency of ∼3cd∕A. Moreover, the Commission Internationale de L’Eclairage coordinates of the emitted light is close to that of pure white light and is insensitive to the applied voltages.

Enhanced performance of white polymer light-emitting diodes using polymer blends as hole-transporting layers

AU: PLEASE CONFIRM CHANGES MADE IN THE BYLINE.White polymer light-emitting diodes (WPLEDs) with the Commission Internationale de l’Enclairage coordinates of (0.32, 0.34) are demonstrated with poly(9,9-dioctylfluorene-2,7-diyl) as host and poly(5-methoxy-2-(2′-ethyl-hexylthio)-p-phenylenevinylene) as guest. Blends of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD) and poly(N-vinyl-carbazole) (PVK) are introduced into bilayer devices as hole-transporting layers (HTLs). Because the blends combined the hole-injection and hole-transporting capabilities of poly-TPD with electron-blocking capability of PVK, WPLEDs with the blends as HTLs exhibit enhanced performance in comparison with single-layer device and bilayer devices with pure poly-TPD or pure PVK as HTL. With a 1:1 weight ratio of poly-TPD to PVK in the blend, the WPLED achieves a maximum brightness of ∼5000cd∕m2 with a maximum electroluminescent efficiency of 3.15cd∕A.

Facile preparation of TiOX film 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.

Simple O2 Plasma-Processed V2O5 as an Anode Buffer Layer for High-Performance Polymer Solar Cells

UNLABELLED A simple O2 plasma processing method for preparation of a vanadium oxide (V2O5) anode buffer layer on indium tin oxide (ITO)-coated glass for polymer solar cells (PSCs) is reported. The V2O5 layer with high transmittance and good electrical and interfacial properties was prepared by spin coating a vanadium(V) triisopropoxide oxide alcohol solution on ITO and then O2 plasma treatment for 10 min [V2O5 (O2 plasma)]. PSCs based on P3HT:PC61BM and PBDTTT-C:PC71BM using V2O5 (O2 plasma) as an anode buffer layer show high power conversion efficiencies (PCEs) of 4.47 and 7.54%, respectively, under the illumination of AM 1.5G (100 mW/cm(2)). Compared to that of the control device with PBDTTT-C:PC71BM as the active layer and PEDOT PSS (PCE of 6.52%) and thermally annealed V2O5 (PCE of 6.27%) as the anode buffer layer, the PCE was improved by 15.6 and 20.2%, respectively, after the introduction of a V2O5 (O2 plasma) anode buffer layer. The improved PCE is ascribed to the greatly improved fill factor and enhanced short-circuit current density of the devices, which benefited from the change in the work function of V2O5, a surface with many dangling bonds for better interfacial contact, and the excellent charge transport property of the V2O5 (O2 plasma) layer. The results indicate that an O2 plasma-processed V2O5 film is an efficient and economical anode buffer layer for high-performance PSCs. It also provides an attractive choice for low-cost fabrication of organic electronics.

High-Performance Small Molecule/Polymer Ternary Organic Solar Cells Based on a Layer-By-Layer Process.

UNLABELLED The layer-by-layer process method, which had been used to fabricate a bilayer or bulk heterojunction organic solar cell, was developed to fabricate highly efficient ternary blend solar cells in which small molecules and polymers act as two donors. The active layer could be formed by incorporating the small molecules into the polymer based active layer via a layer-by-layer method: the small molecules were first coated on the surface of poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) ( PEDOT PSS), and then the mixed solution of polymer and fullerene derivative was spin-coated on top of a small molecule layer. In this method, the small molecules in crystalline state were effectively mixed in the active layer. Without further optimization of the morphology of the ternary blend, a high power conversion efficiency (PCE) of 8.76% was obtained with large short-circuit current density (Jsc) (17.24 mA cm(-2)) and fill factor (FF) (0.696). The high PCE resulted from not only enhanced light harvesting but also more balanced charge transport by incorporating small molecules.

Two color plasmon excitation in an electron-hole bilayer structure controlled by the spin-orbit interaction

The dispersion and intensity of coupled plasma excitation in an electron-hole bilayer with Rashba spin-orbit coupling is calculated. We propose to use the spin-orbit coupling in individual layers to tune the intensity of two plasmons. The mechanism can be used to develop a two color terahertz source with tunable intensities.

Efficient P3HT:PC61BM solar cells employing 1,2,4-trichlorobenzene as the processing additives

The efficiency of the poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) based organic solar cells was enhanced by using 1,2,4-trichlorobenzene (TCB) as a processing additive to control the blend morphology. The addition of TCB improved the arrangement of P3HT which resulted in good phase separated blend films. Correspondingly, the optimized solar cells showed a power conversion efficiency (PCE) of 4.17% with a fill factor (FF) of 0.69, which were higher than those of common thermal annealing devices (PCE 3.84%, FF 0.67). The efficiency was further improved to 4.74% by thermal annealing at 150 °C for 10 min with a higher FF of 0.74.