【作者】 王晓；

【导师】 于军胜；

【作者基本信息】 电子科技大学 ， 光学工程， 2018， 博士

【摘要】 基于有机半导体材料的光电探测器件,由于其材料来源广泛、制备工艺简单、成本低、可柔性化等优点,受到业界的广泛关注。目前,有机光电探测器件（organic photodetectors,OPDs）的研究在国际上还处于起步阶段,尽管取得了显著的进展,但是与无机光电探测器件相比,在探测能力、光谱选择性以及能量损失机理等方面的研究明显滞后。鉴于此,本论文基于不同的有机半导体材料体系,以提高器件的探测性能为目标,从器件结构和制备工艺等方面进行优化设计,探索实现可溶液加工制备的高性能OPDs的新途径;同时,分析研究器件的材料体系-响应光谱特性,以及电荷转移和能量损失机理,为多功能和高性能OPDs的实现提供理论基础。本论文的主要内容分为以下四个方面:1.基于聚乙烯咔唑:富勒烯衍生物材料体系的OPDs的性能研究通过体异质结（bulk heterojunction,BHJ）活性层的调控、功能层的引入和器件结构的优化等方法,提升了OPDs的紫外光探测性能。结果表明:优化活性层厚度和退火温度可以降低器件的暗电流,提高探测率（specific detectivity,D^*）。当活性层厚度为100 nm,退火温度为100 ^oC时,在0.6 mW/cm² 350 nm紫外光照射下,-1.5 V偏压下的D^*为1.07×10¹² Jones;电子阻挡层增加了注入能级势垒,有效阻挡了暗态条件下电子的反向注入,降低了器件的暗电流。当引入8 nm1,1-bis（（di-4-tolylamino）-phenyl）cyclohexane（TAPC）作为电子阻挡层时,器件的D^*提升到5.59×10¹² Jones;基于氧化锌/poly（N,N’-bis-4-butylphenyl-N,N’-bisphenyl）benzidine（poly-TPD）中间连接层的双层结构器件能够有效降低暗电流,增加光响应度,器件的D^*提高了15.6倍。2.基于热激活延迟荧光受体材料的非富勒烯OPDs的性能研究采用三种热激活延迟荧光（thermally activated delayed fluorescence,TADF）作为电子受体材料,研究了TADF材料的选择以及新型器件结构对OPDs紫外探测性能的影响。结果表明:基于poly（N-vinylcarbazole）（PVK）:3,4,5,6-tetrakis（carbazol-9-yl）-1,2-dicyanobenzene（4CzPN）活性层的器件探测性能最优,在0.5 mW/cm² 350 nm紫外光照射下,-9 V偏压下的D^*为1.09×10¹² Jones;通过减小银（silver,Ag）电极的厚度,可以实现半透明紫外OPDs,最优器件可见光透过率达到43%,在同等测试条件下,D^*为2.09×10¹¹ Jones;氧化钼（molybdenum oxide,MoO_x）/Ag/MoO_x叠层结构可以作为高效导电电极取代氧化铟锡（indium tin oxide,ITO）,用于半透明器件的制备。其中,最优器件的可见光透过率达到46.7%,D^*为5.31×10¹⁰ Jones,且器件具有峰值在380 nm处的双侧入射响应特性。3.光谱选择性全聚合物光电探测器件的性能研究采用聚合物作为电子受体材料,系统研究了活性层厚度调控及器件结构对响应光谱特性、探测性能及能量损失机理的影响。结果表明:由于受体层的滤光作用以及载流子传输对厚度的依赖特性,基于双层结构全聚合物OPDs的响应光谱随受体层厚度的改变具有选择性。随着受体层厚度的增加,OPDs由300 nm-750 nm的全光谱响应转变为峰值为450 nm和780 nm波长处的双峰响应,且响应光谱随外加电场的增强而拓宽;基于BHJ结构OPDs,响应光谱随BHJ厚度（150 nm-2μm）的改变具有选择性。当BHJ厚度为150 nm时,实现了响应波段为300 nm-750 nm的全光谱响应OPDs;当BHJ厚度增加到2μm时,实现了峰值响应位于770 nm处的窄带近红外响应OPDs,D^*为1.61×10¹¹ Jones;基于双层和BHJ结构器件中的光学损失率和双分子复合损失率相近,而双层结构OPDs中的一阶复合损失率较低,器件的光响应度较高。4.基于石墨烯材料导电电极、可溶性小分子材料体系OPDs的性能研究基于可溶性小分子材料benzodithiophene-terthiophene-rhodanine（BQR）:[6,6]-phenyl C₇₁butyric acid methyl ester(PC₇₁BM)体系,采用三层石墨烯材料取代ITO作为透明导电电极,制备了柔性OPDs,并研究了界面修饰作用以及器件的能量损失机理。结果表明:界面修饰层MoO_x有效降低了polyethylene terephthalate（PET）/石墨烯电极的表面电阻和粗糙度,增加了电极的功函数;基于PET/石墨烯电极和基于玻璃/ITO电极OPDs的双分子复合损失率相近,而基于石墨烯电极OPDs较低的光响应度主要是由器件内较高的光学吸收损失及一阶复合损失造成的。更多还原

【Abstract】 Photodetectors made of solution-processed organic semiconductors have recently emerged as candidates for the next-generation light detecting.They combine ease of processing,integratable,compatibility with flexible substrates and good performance.Although a significant progress has been made in the field of organic photodetectors（OPDs）,their performance regarding the detectivity,color selectivity and energy losses are still inferior to their inorganic counterparts.In this thesis,we explored ways to improve the overall performance of OPDs by synergistic combining the materials and device engineering.Additionally,the characters of photo-responses and charge transport properties were studied,which provided a better understanding of OPDs fabrication,facilitating the progress toward the realization of next generation high-performance and multifunctional optoelectronics.1 OPDs consisting of a polymer active layer of poly（N-vinyl carbazole）（PVK）:[6,6]-phenyl-C71-butyric acid methyl ester(PC₇₁BM)were fabricated,and the photodetection properties of OPDs were systematically investigated by optimizing the active layer and structure engineering.Through thickness modulation and thermal annealing,the ultraviolet detectivity of OPD was improved with an optimized value of1.07×10¹² Jones under 350 nm-ultraviolet（UV）light illumination（0.6 mW/cm²）.In addition,by inserting an 8 nm-TAPC layer as the electron blocking layer,a remarkable reduction in dark current was achieved with the maximum D^*value of 5.59×10¹² Jones.Lastly,we introduced a double-layer photodetector with zinc oxide（ZnO）/poly（N,N’-bis-4-butylphenyl-N,N’-bisphenyl）benzidine（poly-TPD）interconnecting layer.The device was able to double the photocurrent and reduce the dark current,leading to a remarkably enhanced in detectivity by 15.6 folds.2 Three thermally activated delayed fluorescence（TADF）materials with strong UV absorption were firstly utilized as the electron acceptors in solution-processed OPDs.The best comprehensive detectivity could reach to 1.09×10¹² Jones under 0.5mW/cm² 350 nm UV light at-9 V.Additionly,by using a ultra-thin silver layer as the electrode,visibly semitransparent OPDs with an average transmittance of 43%were obtained,and the detectivity could reach to 2.09×10¹¹ Jones under the same testing conditions.Moreover,by utilizing the molybdenum oxide（MoO_x）/silver（Ag）/MoO_x（MAM）structure as the bottom transparent electrode,high performance indium-tin-oxid（ITO）-free semitransparent OPDs have been realized.The champion device exhibited a high transmittance of 46.7%,and a peak response located at 380 nm.3 PNNT and PNNTH have been prepared as polymeric electron acceptors for OPDs.By tuning the thickness of the active layer,the resultant performance and the charge transport properties of the all-polymer photodetectors were systematic studied.Firstly,the response spectra of OPDs with layer-by-layer（bilayer）structures varied from broadband to narrowband,which was due to the filter effect of PNNT layer.The broadband response showed the visible spectral region of 300 nm-750 nm,while the narrowband responses located at 450 nm and 780 nm,respectivity.Secondly,by tuning the thickness of BHJ from 150 nm to 2μm,spectrally selective all-polymer photodetectors with broad and narrow band responses were realized.The OPDs with 2μm-thickness had a narrowband D^*of 1.61×10¹¹ Jones at 770 nm.Lastly,the bimolecular recombination losses and optical losses were found to be remarkably similar for the two systems,and our observation of the higher light current for bilayer devices was shown to result from the higher charge generation yield due the smaller first-order recombination losses.4 Graphene was developed as the transparent conducting electrode（TCE）for OPDs to meet the requirements for the development of flexible devices.We used a non-polymeric molecular benzodithiophene-terthiophene-rhodanine（BQR）as donor and[6,6]-phenyl C71 butyric acid methyl ester as acceptor to make the bulk heterojunction.The effect of MoO_x were investgated,along with the power loss mechanism within the devices.By utilizing the thermally evaporated MoO_x interlayer,the graphene anode showed a remarkably reduced sheet resistance,smoother surface and increased work function,which leveled the sharp difference in various parameters for ITO and graphene TCEs.In comparison,we found the limited photoresponse in flexible devices were mainly due to the optical losses and less charge generation,although the bimolecular recombination has no function for the loss mechanism.更多还原