N-Benzoimidazole/Oxadiazole Hybrid Universal Electron Acceptors for Highly Efficient Exciplex-Type Thermally Activated Delayed Fluorescence OLEDs

Recently, donor/acceptor type exciplex have attracted considerable interests due to the low driving voltages and small singlet-triplet bandgaps for efficient reverse intersystem crossing to achieve 100% excitons for high efficiency thermally activated delayed fluorescence (TADF) OLEDs. Herein, two N-linked benzoimidazole/oxadiazole hybrid electron acceptors were designed and synthesized through simple catalyst-free C-N coupling reaction. 24iPBIOXD and iTPBIOXD exhibited deep-blue emission with peak at 421 and 459 nm in solution, 397 and 419 nm at film state, respectively. The HOMO/LUMO energy levels were −6.14/−2.80 for 24iPBIOXD and −6.17/−2.95 eV for iTPBIOXD. Both compounds could form exciplex with conventional electron donors such as TAPC, TCTA, and mCP. It is found that the electroluminescent performance for exciplex-type OLEDs as well as the delayed lifetime was dependent with the driving force of both HOMO and LUMO energy offsets on exciplex formation. The delayed lifetime from 579 to 2,045 ns was achieved at driving forces close to or larger than 1 eV. Two TAPC based devices possessing large HOMO/LUMO offsets of 1.09–1.34 eV exhibited the best EL performance, with maximum external quantum efficiency (EQE) of 9.3% for 24iPBIOXD and 7.0% for iTPBIOXD acceptor. The TCTA containing exciplex demonstrated moderate energy offsets (0.88–1.03 eV) and EL efficiency (~4%), while mCP systems showed the poorest EL performance (EQE <1%) and shortest delayed lifetime of <100 ns due to inadequate driving force of 0.47–0.75 eV for efficient exciplex formation

A two-dimensional matrix Padé-type approximation in the inner product space

AbstractBy introducing a bivariate matrix-valued linear functional on the scalar polynomial space, a general two-dimensional (2-D) matrix Padé-type approximant (BMPTA) in the inner product space is defined in this paper. The coefficients of its denominator polynomials are determined by taking the direct inner product of matrices. The remainder formula is developed and an algorithm for the numerator polynomials is presented when the generating polynomials are given in advance. By means of the Hankel-like coefficient matrix, a determinantal expression of BMPTA is presented. Moreover, to avoid the computation of the determinants, two efficient recursive algorithms are proposed. At the end the method of BMPTA is applied to partial realization problems of 2-D linear systems

A Study on the Development Ability of Economic Zones Above Provincial Level in Anhui Province -Based on Principal Component Analysis

This paper uses the principal component analysis method to measure the output capacity, input capacity and comprehensive development capacity of development zones in 2017, taking nine indicators reflecting the economic development capacity of 11 development zones above the provincial level in Anhui Province as the research object. The results show that the development level of 11 development zones in Anhui Province is not high on the whole, and the output capacity and comprehensive development capacity show a trend of polarization; the input capacity has three obvious levels, and the location advantage plays an important role in the development o economic zones

Synthesis of D-pi-A-pi-D Type Dopant-Free Hole Transporting Materials and Application in Inverted Perovskite Solar Cells

Synthesis of D-pi-A-pi-D Type Dopant-Free Hole Transporting Materials and Application in Inverted Perovskite Solar Cell

Achieving over 21% efficiency in inverted perovskite solar cells by fluorinating a dopant-free hole transporting material

Hole transporting materials (HTMs) play a critical role in ameliorating the performance of perovskite solar cells (PSCs). Dedicated HTMs can improve not only the hole extraction and efficiency but also the stability. Herein, PFDT-COOH and its fluorinated derivative, PFDT-2F-COOH, are introduced as dopant-free HTMs for inverted PSCs. Compared to PFDT-COOH, PFDT-2F-COOH exhibits a deeper highest occupied molecular orbital (HOMO) level, a higher work function on indium tin oxide electrodes, and an elevated built-in potential in the device. The PFDT-COOH device based on FA(1-x)MA(x)PbI(3) mixed-cation perovskite exhibits a champion power conversion efficiency (PCE) of 20.64%, while the PFDT-2F-COOH device exhibits a champion PCE of 21.68%, which is close to the highest value (21.7%) attained in inverted single-junction PSCs. The elevated efficiency is attributed to reduction of carrier recombination and enhancement of carrier extraction via the fluorination strategy. In addition, the two devices also show excellent operational and thermal stabilities. Therefore, our work offers a feasible strategy for preparing high efficiency and stable inverted PSCs

Dramatic Enhancement of Power Conversion Efficiency in Polymer Solar Cells by Conjugating Very Low Ratio of Triplet Iridium Complexes to PTB7

Various low ratios of triplet iridium complexes (0, 0.5, 1, 1.5, 2.5, and 5 mol%) are conjugated to the backbone of the famous champion donor polymer PTB7. At the same conditions, the power conversion efficiency for polymer containing 1% of Ir increases by 45%, 39%, and 31% in three batches of devices compared with control Ir-free PTB7