A Robust, High-Temperature Organic Semiconductor

We introduce a new pentacene-based
organic semiconductor, 5,6,7-trithiapentacene-13-one (TTPO). TTPO
is a small-molecule organic semiconductor that is simple to synthesize
and purify, readily crystallizes, melts in air from 386–388
°C without decomposition, and is indefinitely stable against
degradation in acid-free solution. TTPO has a high molar absorptivity,
optical and electrochemical HOMO–LUMO gaps of 1.90 and 1.71
eV, respectively, and can be thermally evaporated to produce highly
uniform thin films. Its cyclic voltammogram reveals one reversible
oxidation and two reversible reductions between +1.5 and −1.5
V. The crystal structure for TTPO has been solved and its unique parallel
displaced, and head-to-tail packing arrangement has been examined
and explained using high-level density functional theory. High-resolution
scanning tunneling microscopy (STM) was used to image individual TTPO
molecules upon assembly on a pristine Au(111) surface in ultrahigh
vacuum. STM images reveal that vapor-deposited TTPO molecules nucleate
in a unique stacked geometry with a small acute angle with respect
to Au(111) surface. Preliminary TTPO-based bilayer photovoltaic devices
show increases in short circuit current density upon heating from
25 to 80 °C with a concomitant 4–160-fold increase in
power conversion efficiencies. TTPO has the potential to be used in
thin-film electronic devices that require operation over a wide range
of temperatures such as thin-film transistors, sensors, switches,
and solar cells.

本研究报道了一种新型并五苯（pentacene）基有机半导体：5,6,7-三硫代并五苯-13-酮（TTPO）。TTPO属于小分子有机半导体（small-molecule organic semiconductor），其合成与纯化简便易行，易于结晶；在空气中于386~388 ℃熔融且无分解现象，在无酸溶液中可长期稳定不发生降解。该材料具有较高的摩尔消光系数（molar absorptivity），其光学与电化学最高占据分子轨道-最低未占据分子轨道（HOMO–LUMO）能隙分别为1.90 eV和1.71 eV；可通过热蒸发工艺制备得到高度均匀的薄膜。其循环伏安图（cyclic voltammogram）显示，在+1.5 V至-1.5 V的电位区间内存在1个可逆氧化峰与2个可逆还原峰。TTPO的晶体结构已被解析，其独特的平行错位、首尾相接堆积构型通过高精度密度泛函理论（density functional theory，DFT）进行了研究与阐释。采用高分辨扫描隧道显微镜（High-resolution Scanning Tunneling Microscopy，STM）对超高真空（ultrahigh vacuum）环境下洁净Au(111)单晶表面组装的单个TTPO分子进行了成像。STM成像结果显示，气相沉积（vapor-deposited）的TTPO分子以独特的堆叠构型成核，该构型与Au(111)表面呈较小锐角。基于TTPO的初步双层光伏器件测试结果表明，当工作温度从25 ℃升至80 ℃时，器件的短路电流密度（short circuit current density）有所提升，同时功率转换效率（power conversion efficiencies）实现4~160倍的增长。TTPO有望应用于需在宽温度范围下工作的薄膜电子器件中，例如薄膜晶体管（thin-film transistors）、传感器（sensors）、开关元件（switches）以及太阳能电池（solar cells）。