基于PIN结构的Rubrene/C70太阳能电池的性能研究

实验制备了ITO/V₂O₅/Rubrene/C₇₀:Rub rene/C₇₀/BCP/Al的PIN结构有机太阳能电池(OSC),其中 Rubrene、Rubrene:C₇₀和C₇₀分别作为P、I和N层。通过改变I层厚度,研究了I 层对OSC性能的影响及作用机理。实验显示,I层厚为5nm时器件的功率转换效率η达到最大值为1.580%,同时 获得了较大的短路电流密度Jsc为4.365mA· cm－2;相对PN结构器件,功率转化效率η短路电流密度Jsc和填充因子FF分别提 高了40.3%、29.7%和8.2%。我们认为,I层中激子分离效率的提高导 致了器件性能的改善。     

石墨烯掺杂Cs2CO3作为高效电子注入层的OLEDs性能研究

研制了石墨烯掺杂Cs₂CO₃(Cs₂CO₃:Graphe ne )作为高效电子注入层、结构为ITO/N,N′-bis-(1-naphthyl) -N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB)(50 nm)/tris-(8-hydroxy quinoline)-aluminum Alq₃(80 nm)/Cs₂CO₃:Gra phene (mss 20% 1nm)/Al(120 nm)的OLEDs。将其与标准器件ITO/NPB(50 nm)/Alq₃(80 n m)/LiF(0.5 nm)/Al(120 nm)作性能比较,研究石墨烯掺杂在Cs₂CO₃中作为电子注入层 对 OLEDs性能的影响。结果表明,基于Cs₂CO₃:Graphene结构作为电子注入层的器 件效率要高于LiF作为电子注入层的器件,其最大电流效率达到2.02 cd/A, 是标准器件的2.59倍;亮度也高于LiF作为电子注入层的器件,在10 V时达 到最大值7690cd/m²,是标准器件最大亮度 的2.07倍。性能得到提高的主要机理是由于Cs₂CO₃:Graphene的引入提高了电子注入效率。     

基于Bphen:BCP:Cs2CO3作为电子传输层的OLED性能研究

为了进一步平衡OLED器件内部空穴和电子载流子 的注入,制备了结构为ITO/NPB(40nm)/Alq₃(45nm)/Bphen:(X%)BCP:(5%)Cs₂CO₃(15nm)/Cs₂CO₃(1.5 nm)/Al(100nm)的OLED器件,通过改变BCP 的掺杂浓度,研究了以Bphen:BCP:Cs₂CO₃作为电子传输层对OLED器件发光亮度、电流 密度和效率等性能 的影响。结果表明,采用Bphen:BCP:Cs₂CO₃作为电子传输层能提高器件的电子注入能力 ,改善器件的性能, 相比于未引入BCP的器件,采用BCP掺杂浓度为10%的Bphen:BCP:Cs₂CO₃作为电子传输层 ,可以使器件 的最大电流效率提高46%,达到3.89cd/A,且 在电压从为5V上升至10V的过程中,器件的色坐标一直为 (0.35,0.55),具有很高的稳定性。原因是由于BCP的高LUMO能级和高 HOMO能级,能够有 效阻挡空穴到达阴极,减小空穴漏电流,同时使电子的注入更容易,电子和空穴的注入更加 平衡,发光也更加稳定。     

WO3对Rubrene/C70有机太阳能电池性能的改善

研究了WO₃对Rubrene/C₇₀有机太阳能电池 (OSCs)性能的 改善,制备了结构为ITO/WO₃/Rubrene/C₇₀/BCP/Al的OSCs,其中WO₃插入在I TO和Rubrene中间作为阳极修饰层。通过优化WO₃的厚度,研究了WO₃对OSCs性能的改善及其作用机理。实验发现,器件的短路电流Jsc、开路电压V_oc、 填充因子(FF)、光电转换效率(PCE)和串联电阻Rs等性能参数随WO₃厚度的变化呈规律性变化;当 WO₃厚度小于80 nm时,器件PCE随着厚度的增加不断增大;当W O ₃厚大于80 nm时,器件PCE随着厚度的 增加不断减小;当WO₃厚度为80 nm 时,器件PCE达到最高为1.03%, 相应的J sc、V_oc、FF分别为2.81mA·cm－2、 0.83V、43.85%,Rs为45.3Ω·cm²,对比没有WO₃修饰层, 器件的J_sc、V_oc、FF和PCE分别提高了31%、137%、17%,Rs降低了33%。     

TiO2基染料敏化太阳能电池的表面修饰及性能研究

采用水热法制备TiO₂浆料,用La(NO₃)₃溶 液浸泡TiO₂薄膜获得修饰电极。用X射线光电子能谱(XPS) 和扫描电子显微镜(SEM)对修饰电极的主要成分及形貌进行表征的结果显示,电极薄膜分为 上下两层,表 面包覆层粒径较大,为La₂O₃颗粒;下层颗粒粒径较小,为TiO₂颗粒。电流-电压测 试结果显示,与修饰 前相比,用La(NO₃)₃溶液浸泡30min获得的膜电极性能最优,使 开路电压和短路电流分别提高了6.8%和 18.5%。电化学阻抗谱(EIS)测试结果表明,相同偏压下,TiO₂/La ₂O₃电极界面复合电阻比TiO₂要大,说明 La₂O₃包覆层在一定程度上抑制了界面的电子复合,改善了电池的光电化学性能。     

双阴极修饰层改善Rubrene/C70有机太阳能电池的性能

采用NTCDA/PTCBI双阴极修饰层制备了结构为ITO /MoO₃/Rubrene/C70/NTCDA/PTCBI/Al有机太阳能 电池(OSC),研究了双阴极修饰层对Rubrene/C70 OSC性能的影 响。实验结果表明,引入双阴极修饰层 后,器件的各性能参数有了显著提高。通过对PTCBI厚度优化发现,当PTCBI厚为5nm时器件 的各性 能参数最佳,器件的功率转换效率(PCE)=3.19%,电流密度Jsc=8.99mA·cm－2,开路电 压Voc=0.85V, 填充因子(FF)=41.58%,与未插入PTCBI 层相比器件的各性能分别提高了538%、338.5% 、13.3%和16.5%。     

ZnO缓冲层改善Rubrene/C70有机太阳能电池的性能

通过制备结构为ITO/ZnO/C₇₀ /Rubrene/MoO₃/Al 的有机太阳能电池(OSCs),研究了ZnO作为阴极 修饰层对Rubrene/C70有机太阳能电池性能的改善。同时通过 优化ZnO的厚度研究了ZnO的工作机理。 从实验结果可以看出,随着ZnO厚度的变化,器件的短路电流密度(J_sc)、开路电压(V_oc)、填充因子 (FF)、光电转换效率(PCE)和串联电阻(R_s)等性能参数呈现出了规律 性变化,当ZnO层厚度比较 薄时,器件PCE随着厚度的增加不断增大,当ZnO层厚度为53nm时,器件PCE达到最高为1.13%, 对应的J_sc、V_oc、FF分别为2.82mA·cm－2、0. 84V、45.86%,R_s为66.2Ω·cm²,当ZnO层厚度继续增 加时,器件PCE开始减小。对比没有ZnO阴极修饰层,器件最优时 的Jsc、V_oc、FF和PCE 分别提高了49%、17%,R_s降低了56%。     

退火温度对银-二氧化硅核壳(Ag@SiO2/TiO2)薄膜结构，光学特性以及光催化性能的影响

局部表面等离子共振广泛应用于光催化和太阳能 电池等领域。采用电子束和热沉积技 术,在融石英和Si片上制备了Ag@SiO₂/TiO₂薄膜。在300 ℃,400 ℃,500 ℃,600 ℃ 温度下,薄膜在空气氛围下退火2h。采用拉曼光谱仪,紫外-可见分光光度 计(UV-Vis)等手段对微结构,光学性能等特性进行了表征。利用能谱仪测定了元素成分及含 量。考察了薄膜在水溶液中降解甲基橙的光催化活性。结果表明:Ag@SiO₂/TiO₂薄膜具有优 异的光催化性能。测试结果表明:在250℃下制备的TiO₂薄膜为无定形结构;在本实验条 件下,随着退火温度的升高,薄膜呈锐钛矿结构;锐钛矿相表现出了更好的光催化性能。     

TiO2表面预处理对钙钛矿太阳电池性能的影响

采用一步法制作了基于 n-i-p结构的钙钛矿太阳电池。为了提高钙钛矿活性层以及TiO₂与钙钛矿活性层接触面的质量,用 MAI、MABr和PbI₂溶液对TiO₂层进行预处理,研究了预处理对电池性能的影响。结果显示对TiO₂进行预处理能够改善钙钛矿活性层薄膜的质量并提升钙钛矿太阳电池的性能。通过溶液预处理,太阳电池的能量转换效率和器件稳定性有显著提高,同时滞后效应明显减弱。     

MoO3修饰氧化石墨烯作为空穴注入层影响研究

研究了MoO₃修饰氧化石墨烯(GO)作为空穴注入层的影响。采用旋涂的方法制备了GO, 再真空蒸镀修饰层MoO₃,得到了空穴注入能力强和透过率高的复合薄膜。MoO₃的厚分 别采用0、3、5和8nm。通过优化MoO₃的厚度发现,当MoO₃的厚为5nm时,复合薄膜 的透过率达到最大值,在 550nm的光波长下透光率为88%,且此时采用 复合薄膜作为空穴注入层制备的结构为 ITO/GO/MoO₃(5nm)/NPB(40nm)/Alq₃(40nm)/LiF(1nm)/Al(100nm)的有机电致发光器件(OLED)性能 最佳。通过对OLED进一步的优化,改变Alq₃的厚度,分别取50、60和70nm,测量其电压 、电流、亮度、色坐标和电致发光(EL)光谱等参数发现,当Alq₃的厚为50nm时器件性能最 佳。最终制备了结构为ITO/GO/MoO₃(5nm)/NPB(50nm)/Alq₃(50nm)/LiF(1nm)/Al(100 nm)的OLED,在电压为10V时,最大电流效率达到5.87cd/A,与GO单独作为空穴注入层制备的器件相比,提高了50%。     

Reactive ion etching of gallium nitride films

Reactive ion etching (RIE) was performed on gallium nitride (GaN) films grown by electron cyclotron resonance (ECR) plasma assisted molecular beam epitaxy (MBE). Etching was carried out using trifluoromethane (CHF₃) and chloropentafluoroethane (C₂ClF₅) plasmas with Ar gas. A conventional rf plasma discharge RIE system without ECR or Ar ion gun was used. The effects of chamber pressure, plasma power, and gas flow rate on the etch rates were investigated. The etch rate increased linearly with the ratio of plasma power to chamber pressure. The etching rate varied between 60 and 500Å/min, with plasma power of 100 to 500W, chamber pressure of 60 to 300 mTorr, and gas flow rate of 20 to 50 seem. Single crystalline GaN films on sapphire showed a slightly lower etch rate than domain-structured GaN films on GaAs. The surface morphology quality after etching was examined by atomic force microscopy and scanning electron microscopy.     

利用Cs2CO3和Cs2CO3:BPhen改善OLED的光电性能

碳酸铯(Cs2CO3)是优秀的电子注入材料,本文通过器件ITO/MoO3(3nm)/NPB(40nm)/C545T:Alq3(99∶1,30nm)/Alq3(30nm)/Cs2CO3(xnm)/Al(100nm)优化了Cs2CO3作为电子注入层(EIL)的厚度。Cs2CO3作为EIL,提高了器件的电子注入能力,使更多的电子得以与空穴在发光层复合发光。实验结果表明,Cs2CO3作为EIL的优化厚度为1.5nm时,对应器件的效率是不含Cs2CO3的3倍以上。在Cs2CO3作为EIL的基础上,研究器件结构为ITO/NPB(40nm)/Alq3(45nm)/Cs2CO3:Bphen(0%,5%,10%,15nm)/Cs2CO3(1.5nm)/Al(100nm)时不同浓度的Cs2CO3掺杂电子传输层Bphen(Cs2CO3:Bphen)对器件性能的影响。结果表明,Cs2CO3掺杂浓度较低时(5%)能进一步改善器件的电子传输和注入能力,进而提高器件的发光效率;而掺杂浓度较高时(10%),由于Cs扩散严重,形成淬灭中心,使得发光效率衰减严重。     

Low-cost supercritical CO2/H2O2 treatment on ITO anodes of fluorescent organic light-emitting diodes

A simple and cost-effective approach is proposed as an alternative to conventional oxygen plasma treatment to modify surface property of Indium tin oxide (ITO) anode of a fluorescent organic light-emitting diode (OLED). This was achieved by treating the ITO anode in supercritical CO₂ (SCCO₂) fluids with hydrogen peroxide (H₂O₂). The SCCO₂/H₂O₂ treatment yielded an ITO work function of 5.35 eV after 15 min treatment at 85 °C and 4000 psi, which was significant higher than 4.8 eV of the as-cleaned ITO surface and was slightly less than 5.5 eV of the ITO surface treated by oxygen plasma. The highest work function achieved was 5.55 eV after 45 min SCCO₂/H₂O₂ treatment. The SCCO₂/H₂O₂ treatment can be used to tailor the ITO work function through changing the operation pressure of the treatment. In addition, the correlated dependence of OLED performance on the ITO anodes with and without the treatments was investigated. The maximum power efficiency of 1.94 lm/W was obtained at 17.3 mA/cm² for the device with 15 min SCCO₂/H₂O₂ treatment at 4000 psi. This power efficiency was 19.3% and 33.8% higher than those of the oxygen plasma treatment and as-clean, respectively. The improvement in device efficiency by the SCCO₂/H₂O₂ treatments can be attributed to enhanced hole injection and balance in charge carriers due to increased work function and surface energy of the ITO anodes.     

Superior suppression of gate current leakage in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors

AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al₂O₃/Si₃N₄ bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si₃N₄-based MIS-HFET devices. Al₂O₃/Si₃N₄ bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si₃N₄-based MIS devices under reverse gate bias, and leakage as low as 1×10⁻¹¹ A/mm at −15 V has been achieved in Al₂O₃/Si₃N₄-based MIS devices. By using ultrathin Al₂O₃/Si₃N₄ bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si₃N₄-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al₂O₃ and nitrides. This work demonstrates that Al₂O₃/Si₃N₄ bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.     

Photo-degradation of the indium tin oxide (ITO)/organic interface in organic optoelectronic devices and a new outlook on the role of ITO surface treatments and interfacial layers in improving device stability

This work focuses on the effect of light exposure on ITO/organic interface in organic optoelectronic devices, including organic light emitting devices (OLEDs), organic photo-detectors (OPDs) and organic solar cells (OSCs). The results show that irradiation by light in the visible and UV range leads to a gradual deterioration in charge injection and extraction across the interface. A correlation between the performance stability of the devices and the photo-stability of the ITO/organic contacts is established. Studies also show that this photo-induced degradation can be significantly reduced by means of ITO surface treatment or through the insertion of interfacial layers between ITO and the organic layers. X-ray Photoelectron Spectroscopy (XPS) measurements reveal detectable changes in the interface characteristics after irradiation, indicating that the photo-degradation of the ITO/organic contacts is chemical in nature. Changes in XPS characteristics after irradiation suggest a possible reduction in bonds between ITO and its adjacent organic layer. The results shed light on a new material degradation mechanism that appears to have a wide presence in ITO/organic contacts in general, and which may play a key role in limiting the stability of various organic optoelectronic devices such as OLEDs, OSCs and OPDs.     

共沉淀法制备Y2O2SO4:Eu3+荧光粉及其光致发光研究

采用商业Y(NO3)3·6H2O、Eu(NO3)3·6H2O、(NH4)2SO4和NaOH为实验原料,通过共沉淀法制备了Y2O2SO4:Eu3+荧光粉。利用热分析(DTA-TG-DTG)、傅里叶变换红外(FT-IR)光谱、X射线衍射(XRD)、扫描电子显微镜(SEM)和光致发光(PL)光谱等手段对合成的粉体进行了表征。结果表明,当(NH4)2SO4引入到反应体系中时,前驱体具有非晶态结构,且在空气气氛中800℃煅烧2h能转化为单相的Y2O2SO4粉体,该Y2O2SO4粉体呈准球形,粒径范围分布在0.5~1.0μm之间,团聚较严重。PL光谱分析表明,在270nm紫外光激发下,Y2O2SO4:Eu3+荧光粉呈红光发射,主发射峰位于620nm,归属于Eu3+的5D0→7F2跃迁。Eu3+的猝灭浓度是5 mol%,其对应的荧光寿命为1.22 ms。另外,当(NH4)2SO4未引入到反应体系中时,采用类似的方法合成了Y2O3:Eu3+荧光粉,并对Y2O2SO4:Eu3+和Y2O3:Eu3+荧光粉的PL性能进行了比较。     

Growth and optical properties of strained (AIP)n (GaP)n short-period superlattices

Biaxial tensile strain is introduced into (AlP)_n(GaP)_n superlattices (SLs) by growing the SLs on slightly lattice-mismatched InGaP intermediate layers on GaP(00l) substrates. A significant enhancement of photoluminescence intensity is observed for the strained (AlP)_n (GaP)_n short-period SLs, especially for those with n≤ 3.     

Ag(Ta,Nb)O3 thin-film interdigital capacitors for microwave applications

Epitaxial silver tantalate-niobate Ag(Ta,Nb)O₃ (ATN) films have been grown on LaAlO₃(0 0 1) single crystals by pulsed laser ablation of stoichiometric AgTa_0.38Nb_0.62O₃ ceramic target. Extensive X-ray diffraction analysis reveals epitaxial relationship between the ATN film and LaAlO₃(0 0 1) substrate. Micrometer size interdigital capacitor structures have been defined photolithographically on the top surface of ATN films. ATN/LaAlO₃ thin-film capacitors exhibit superior overall performance: loss tangent as low as 0.0033 at 1 MHz, dielectric permittivity 224 at 1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range. Dielectric permittivity and loss tangent were also measured at the microwave range. Conformal mapping techniques were employed to extract dielectric properties of ATN film on substrate at the microwave frequency range. Theoretical properties of conformal mapping techniques for interdigital capacitors and CPW microstrip lines were discussed.     

High electric-field-induced strain beahvior of single-crystal Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-xPbTiO<Subscript>3</Subscript> multilayer piezoelectric actuators

Two 10-mm-long multilayer prototype actuators were fabricated by a stack method using 55 pieces of 5 mm×5 mm×0.15 mm Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) single crystals and PZT-5A ceramics, respectively. The strain values for PMNT multilayer piezoelectric actuators are twice those of PZT-5A multilayer actuators, and 20.8-μm displacements can be achieved at the same E-field of 15 kV/cm. Although thermal and electrical history markedly impact dielectric and piezoelectric performance of PMNT crystals, the PMNT multilayer actuator can still achieve large displacements with approximately linear behavior below 60°C. Broad stable dynamic displacement characteristic and fast displacement response make the new-type actuators promising candidates for the application in new-generation high-performance solid-state actuators.     

Role of high energy photons in dual spectral source rapid isothermal CVD

The use of tungsten halogen lamps and the deuterium lamp as the source of thermal and optical energies has been exploited to deposit thin films of Ta₂O₅ on Si and conducting substrates. The leakage current densities are as low as 10⁻¹⁰ A/cm² for gate voltage under 5V. Photons in visible, ultraviolet, and vacuum ultraviolet (λ<800 nm) regions provide higher bulk and surface diffusion coefficients as well as reduced activation energy for the chemical process involved in the chemical vapor deposition process. The low thermal mass of the substrate provides limited reaction processing capability. The photochemical and photophysical processes allow the participating atoms and molecules to adjust their bond geometries and occupy sites which result in overall reduction of stress and strain energy and provide materials with overall low microscopic defects at low processing temperature and with high throughput. New experimental results of Al-Ta₂O₅-Si₃N₄-poly Si-Al structure are presented. The leakage current-voltage characteristics are better than those reported by other researchers.