【作者】 孟凡旭；

【导师】 陈维友；

【作者基本信息】 吉林大学 ， 微电子学与固体电子学， 2014， 博士

【摘要】 有机电子学在过去的60多年里一直是物理和化学领域的一大研究热点。由于具有成本低，质量轻和可制备大面积器件等优点，有机半导体非常有潜力成为无机半导体的替代材料。近年来，在有机半导体材料研究方面所取得的显著进展使有机光电器件的研制成为了可能，如有机发光二极管OLED、有机光伏器件OPV和有机光探测器件OPD等。尤其是OLED，如今已经在平板显示和室内照明方面达到了商业化应用的水平。但是目前OPV和OPD的性能与实用化的目标还有一定的距离，所以对于OPV和OPD的研究还有很长一段路要走。基于导电聚合物的光电器件作为有机光电器件中的一类，由于具有相对较高的性能和相对简单的溶液制备方法，近几年得到了非常广泛的研究。本论文的工作研究了低维无机纳米材料对于聚合物太阳能电池和有机/无机杂化紫外光探测器性能的影响。在聚合物太阳能电池方面:尽管目前新型的窄带隙聚合物给体材料层出不穷，但由于在450-600nm蓝绿光波段具有良好的吸收和较高的载流子迁移率，P3HT仍然是难以被取代的聚合物给体材料之一。若要从根本上提高P3HT/PCBM共混太阳能电池的能量转换效率，除了改善器件对入射光的利用率之外，必须突破材料自身固有的限制，进一步提高电池器件的开路电压。首先，采用NaF、YCl3·xH2O作为前驱体反应物，PVP作为表面活性剂，通过方法简便的溶剂热法合成了PVP包覆的NaYF4纳米颗粒。XRD数据显示，制备的纳米颗粒为立方相的β-NaYF4；SEM和TEM的表征结果表明，纳米颗粒的粒径分布在30-45nm之间。而且，可以清楚的观察到在纳米颗粒表面包覆有一层薄薄的PVP，使得NaYF4纳米颗粒能够溶于P3HT:PCBM的邻二氯苯混合溶液中。然后，将制备好的NaYF4纳米颗粒按不同质量比掺入到P3HT:PCBM（1:1）的邻二氯苯混合溶液中配制成有源层溶液，并设计制作结构为ITO/TiO2/P3HT:PCBM:NaYF4/WO3/Ag的聚合物体异质结太阳能电池器件。当NaYF4纳米颗粒的质量分数为0.45wt%时，器件的性能达到最优，对应的光伏性能参数为：开路电压为0.62V，短路电流密度为9.63mA/cm2，填充因子为58.3%，能量转换效率为3.48%，与无纳米颗粒掺杂的器件相比，器件性能得到了明显的提升。通过对掺入质量分数为0.75wt%的PVP且结构为ITO/TiO2/P3HT:PCBM:PVP/WO3/Ag的对比器件的研究发现，器件开路电压的提升主要是由包覆在NaYF4纳米颗粒表面的PVP引起。由于PVP能够与PCBM形成电荷转移复合物，而且PVP的HOMO能级（-5.93eV）比P3HT的HOMO能级（-5.21eV）更深，所以掺入PVP能够增大有源层的有效带隙，提高器件的内建电势，从而提高器件的开路电压。但是没有了NaYF4纳米颗粒载体，器件的填充因子明显变差。通过对没有WO3空穴传输层的且结构为ITO/TiO2/P3HT:PCBM:NaYF4/Ag的对比器件的研究发现，纳米颗粒的引入可以改善有源层的内部形貌，有效地提高器件的填充因子。通过对NaYF4颗粒掺杂的且器件结构为ITO/PEDOT:PSS/P3HT:PCBM:NaYF4/LiF/Al的正型结构对比器件的研究发现，PVP包覆的NaYF4纳米颗粒对基于P3HT:PCBM共混有源层的聚合物体异质结太阳能电池器件性能的提升是具有普遍性的，与器件是否为正型或者反型结构无关。在有机/无机杂化紫外光探测器方面：基于GaN、SiC或金刚石等无机宽禁带半导体材料的紫外光探测器一般需要通过金属有机化学气相沉积（MOCVD）或分子束外延（MBE）等复杂的制备方法来实现，导致探测器的生产成本较高。而且，无机半导体材料的禁带宽度调节起来也十分困难。相比之下，有机半导体材料及其与无机半导体材料形成的杂化材料为低成本、可大面积制备的紫外光探测器件的实现提供了相对简单的途径。另外，通过调整有机材料的化学结构可以比较容易地调节材料的吸收边位置，所以基于这类材料的紫外光探测器件在实现光响应的光谱选择特性时表现的更为灵活。基于以上原因，本论文选取带隙较宽且具有空穴传导能力的聚乙烯基咔唑（PVK）作为电子给体材料，N型的TiO2二维纳米碗阵列（NBs）作为电子受体材料，并利用PVK/TiO2NBs异质结制成具有光谱选择特性的有机/无机杂化紫外光探测器。首先，利用聚苯乙烯（PS）小球胶体模板法和溶胶-凝胶法在ITO衬底表面制备一层高度有序的TiO2二维纳米碗阵列。重点研究了TiO2溶胶溶液的浓度对纳米碗阵列形貌的影响，经过优化后制备得到的TiO2纳米碗结构的直径约为375nm,碗壁高度约为50nm，宽度约为100nm。由于TiO2的比表面积比较大，可以增加PVK和TiO2异质结的作用面积。然后，在TiO2二维纳米碗阵列结构表面旋涂一层PVK薄膜，制成结构为ITO/TiO2NBs/PVK/WO3/Ag的有机/无机杂化紫外光探测器器件。ITO在作为电极的同时，还起到了短波长滤镜的作用，使器件表现出了一定程度的光谱选择特性。器件的具体性能参数为：器件的光响应度峰值位于330nm处，十分靠近UV-B波段（280-320nm），响应波长范围290-375nm，半峰宽约为38.5nm，且在光照强度为144mWcm-2、波长为330nm的紫外光照射条件下，偏压为-5V时，响应度峰值约为8.14A/W。通过对TiO2二维纳米碗阵列正面和背面的反射光谱进行研究发现，纳米碗阵列结构正面在330nm纳米处存在一个反射峰，而背面在375nm处存在一个反射峰，这对整个器件的波长选择特性具有积极的作用。更多还原

【Abstract】 Organic electronics has been the focus of a growing body of investigation in the fieldsof physics and chemistry for more than60years. Organic semiconductors are expected tobe a potential alternative to the inorganic counterparts, due to their peculiar advantages,such as low cost, light weight, large-area fabrication, and so on. And the significant researchprogresses of organic semiconductors provide a feasible way to fabricate organicoptoelectronics devices, such as organic light-emitting diodes (OLEDs), organicphotovoltaic devices (OPVs), and organic photodetectors (OPDs). Especially, OLED hasbeen successfully applied for commercial use in display and interior illumination today.However, the performance of OPV and OPD has not been good enough yet for practicalapplication. Thus, there is a long way to go for the research of OPV and OPD. Conductingpolymer based optoelectronics devices, which belong to the category of organic electronicsdevices, are widely investigated in recent years due to their comparatively higherperformance and solution process. In this work, we investigated and identified the influenceof low dimensional inorganic nanomaterials on the performance of polymer solar cells(PSCs) and organic/inorganic hybrid ultraviolet photodetectors (UVPDs).Polymer solar cells:Even though the low-bandgap conjugated polymer donor materials emerge in anendless stream now, poly(3-hexylthiophene)(P3HT) is still one of the most popular donormaterials due to its high electron mobility and good absorption at the wavelength band of450-600nm. For the purpose of fundamentally enlarging the power conversion efficiency of polymer solar cells based on P3HT:PCBM bend, an further enhancement in the open-circuitvoltage of the devices is needed by breaking the intrinsic limitation of materials, besides theimprovement in the utilization of incident light.Firstly, NaYF4nanoparticles (NPs) was prepared by a facile solvothermal approachusing NaF and YCl3·xH2O as precursors, and polyvinylpyrrolidone (PVP) as a surfactant.The X-ray diffraction peaks of NaYF4sample are in good agreement with the data ofcubic-phase NaYF4nanocrystals. From the image of SEM and TEM, it can be estimatedthat the as-prepared NaYF4NPs have an average size of30-45nm, and a thin layer of PVPcapping on the surface of NPs can be observed clearly, which makes the NPs well dispersedin the blend of P3HT:PCBM in o-dichlorobenzene.Secondly, the NaYF4NPs were blended into the P3HT:PCBM solution with differentweight ratios, and the polymer bulk heterojunction (BHJ) solar cells were fabricated with astructure of indium tin oxide (ITO)/nano-crystal titanium dioxide(nc-TiO2)/P3HT:PCBM:NaYF4NPs/tungsten oxide (WO3)/silver (Ag). Comparing with theundoped devices, the best performance was achieved for the device with0.45wt%NPs,which exhibited a power conversion efficiency (PCE) of3.48%with short-circuit currentdensity (Jsc) of9.63mA/cm2, open-circuit voltage (Voc) of0.62V, and fill factor (FF) of58.3%under AM1.5G illumination with an intensity of100mW/cm2.A control experiment was performed by simply adding PVP (1mg/ml) into theformulation without the NPs. The result showed that the enhanced Voc could be attributedto the incorporation of PVP，which can form into charge transfer complex (CTC) withPCBM and have a deeper HOMO level (-5.93eV) than that of P3HT (-5.21eV). Therefore,the effective bandgap of BHJ can be enlarged due to the addition of PVP, leading to ahigher build-in potential. The Voc was eventually enhanced as a result. However, the devicegot a poor FF by simply adding PVP without NPs carriers.The devices without the hole selective layer of WO3were also fabricated with astructure of ITO/TiO2/P3HT:PCBM:NaYF4/Ag. The result showed that FF can be effectively improved by the introduction of NaYF4NPs, which can tune the internalmorphology of the active layer.The non-inverted standard cell with an architecture of ITO/PEDOT: PSS/P3HT:PCBM:NPs/LiF/Al was also fabricated. The results showed that the NaYF4NPs cappedwith PVP played a positive role in both inverted and non-inverted cells.Organic/inorganic hybrid ultraviolet photodetectors:UVPDs based on individual inorganic wide-bandgap semiconductors such as GaN, SiC,or diamond would require complicated fabrication processes, such as metalorganic chemicalvapor deposition (MOCVD) and molecular beam epitaxy (MBE), leading to a high cost. Inaddition, it’s hard to modulate the bandgap of inorganic semiconductors. Organicsemiconductors or their hybrids with inorganic semiconductors by contrast have provided acomparatively simple way for UV detection to achieve low cost and large-sale application.Since the absorption of organic materials can be easily tuned by tailoring their chemicalstructure, UVPDs based on these materials seem to possess more flexibility in realizing aspectral selective response.According to the above reasons, the high spectrum selectivity hybrid ultravioletphotodetectors were fabricated with poly(N-vinylcarbazole)(PVK) and a n-type2D TiO2nanobowls (NBs) array as the electron donor and acceptor, respectively.Firstly, the highly ordered2D TiO2NBs array was prepared on the surface of ITOsubstrate via a sol–gel method and using colloidal templates of polystyrene (PS) spheres.The influences of the TiO2sol concentration on the morphology of2D TiO2NBs array wereinvestigated. The finally prepared TiO2NBs have a diameter of about375nm, and theridges are about50nm high and100nm thick. The effective area of PVK/TiO2heterojuntion can be reasonably increased due to the large surface area of TiO2NBs.Secondly, the organic/inorganic hybrid UVPDs were fabricated with a structure ofITO/TiO2NBs/PVK/WO3/Ag. The ITO substrate acted as not only an electrode but also aoptical filter for short wavelength. The spectral selectivity of the device was achieved by theinterplay of the transmission of ITO and the absorption of TiO2NBs and PVK together. The response peak of the devices centered at330nm with a full width at half maximum of38.5nm, which is very close to the ultraviolet-B band (UVB,280–320nm). The bestperformance of the device is observed at330nm by applying a bias of-5V, correspondingto a photoresponsivity of8.14A/W under the illumination of144mW/cm2330nm UVlight.The reflectance spectra of the TiO2NBs array from the top and bottom were alsostudied. An obvious reflectance peak is obtained at330nm when the NB array isilluminated from the top, which will help PVK to efficiently reuse the330nm UV lightreflected by the Ag electrode. Meanwhile, there is a significant reflectance peak at375nmwhen the NBs are illuminated from the bottom, which can also contribute to the sharplong-wave photoresponse onset at375nm.更多还原