顶部发射绿色磷光OLED的制备与瞬态性能研究

用磷光材料Ir(ppy)3制备了高效率顶部发射绿色有机发光二极管(OLED),器件的结构为:ITO/Ag/NPB/Ir(ppy)3(5wt%):TPBI/TPBI/LiF/Al。研究发现与传统的无微腔结构器件相比顶部发射器件的性能有大幅度提高,其最大效率为18cd/A。通过使用F-P腔,器件的电致发光(EL)寿命由7.6μs降低为7.1μs,有效地缓解了效率随电流密度增大而下降的问题。顶部发射器件EL共振的主峰位于505nm处,发射光谱半峰宽(FWHM)窄化为23nm,色纯度为(x=0.122,y=0.671),发射光随探测角度变化较小。最后,分析了其瞬态光电性能变化原因。     

不同发光层基质材料的高效红色有机电致磷光器件

制备了以铱配合物(btp)2Ir(acac)磷光体为掺杂剂,分别以TPBi、 CBP 和Alq为发光层基质的红色电致磷光器件,比较了三种器件的性能.结果表明,在三种器件中,以Alq为基质的器件效率极低;以CBP为基质的器件,高的效率和好的色度相互矛盾;以TPBi为基质的器件性能最好,在驱动电流为4 mA/cm2时,色坐标为(x=0.62,y=0.35),亮度效率达2.43 cd /A.分析表明, (btp)2Ir(acac)分子在TPBi基质中的高效发光源于其对空穴的有效俘获.进一步的研究确定,(btp)2Ir(acac)分子在TPBi基质中的激子扩散长度为20 nm左右.     

NPB厚度对堆叠式白光OLED性能的影响

主要研究了NPB厚度对堆叠式白色有机电致发光器件性能的影响。实验制备了四组结构为ITO/2-TNATA(15 nm)/NPB(Tnm)/ADN(30 nm):TBPe(2%):DCJTB(1%)/Alq3(20 nm)/LiF(1 nm)/Al(100 nm)(其中T分别为15,30,35和40 nm)的OLED器件,比较了不同厚度情况下OLED器件的电致发光特性,结果表明:改变NPB(4,4-N,N-bis-N-1-naphthy1-N-pheny1-amino-bipheny1)的厚度能够明显提高器件的发光亮度和发光效率,并调节载流子复合区域的位置,有效提高载流子的注入效果。同时发光器件的颜色也可通过调节NPB层的厚度来改变,这种器件使用NPB作为空穴传输层显示出了色纯度高、亮度好、效率较高的白光发射,其具有CIE色坐标(x=0.301 6,y=0.338 5),最高亮度和最大发光效率分别达到14 020 cd/m2与2.94 lm/W。     

利用Ir(ppy)_3敏化CzHQZn提高OLED的性能

用CzHQZn作为受主,利用磷光敏化的方法制备了有机电致黄光和白光器件。黄光器件采用Ir(ppy)3掺杂4,4-N,N′-=咔唑基联苯(CBP),敏化新的黄光材料CzHQZn作为发光层,当发光层厚度为18nm时器件性能最好,最大发光效率为3.26cd/A(at10V),最大发光亮度为17560cd/m2(at10V);白光器件采用多发光层结构,结合ADN的蓝光复合发光,同时加入了电子阻挡层(NPBX)和空穴阻挡层(BCP),获得的白光器件最大发光效率为2.94cd/A(at8V),最大亮度为11089cd/m2(at13V)。     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

具有低欧姆接触电阻的高性能AlGaN/GaN HEMT器件研制

研究了AlGaN/GaN HEMT器件Ti/Al/Ti/Au四层金属结构欧姆接触的形成过程.通过系统研究退火条件获得了较低的欧姆接触电阻,实现了10-7Ω·cm2的欧姆接触率,并在此基础上对AlGaN/GaN HEMT欧姆接触形成机理进行了深入讨论.通过器件工艺的优化,研制了高性能的AlGaN/GaN HEMT器件.栅宽40μm的器件跨导达到250mS/mm,fT达到70GHz;栅宽0.8mm的功率器件电流密度达到1.07A/mm(Vg=0.5V),Vds=30V时,8GHz工作频率下(在片测试)器件的输出功率为32.5dBm(1.6W),输出功率密度达到2.14W/mm,功率增益为12.7dB.     

基于溶液法制备的高效率磷光有机发光二极管

溶液法制备的有机发光二极管(OLED)虽然有着制作成本低、材料利用率高以及容易大规模生产等优势,但是在器件效率上离传统高温真空热蒸镀法制作的OLED还有很大差距.文章基于一种新型的磷光发光材料Ir(tfmppy)2 (tpip),在利用单一主体材料溶液法制备OLED时发现器件效率不高,同时效率滚降很大.为了提高器件效率,同时减小效率滚降,以多种材料混合作为主体材料.通过改变混合主体材料间的比例关系,以一种简单的器件结构,采用溶液法制作出了高效率的OLED器件.其中,以质量比为7∶21∶12的PVK∶mCP∶TCTA为混合主体材料,掺杂质量比为10％的Ir(tfmppy)2 (tpip)作为发光层的器件,取得了高达55 cd/A的电流效率.     

Electron Injection Enhancement by Diamond-Like Carbon Film in Polymer Electroluminescence Devices

用正丁胺作碳源,采用射频辉光等离子系统制备类金刚石碳膜(DLC),沉积在聚合物发光器件中的发光层(MEH-PPV)和铝(Al)阴极间作电子注入层.制备了结构为ITO/MEH-PPV/DLC/Al的不同DLC厚度的器件,测量了器件的I-V特性、亮度及效率,研究了DLC层对器件电子注入性能影响的机制.结果表明:当DLC厚度小于1.0nm时,其器件有较ITO/MEH-PPV/Al高的启动电压和低的发光效率;当DLC厚度在1.0～5.0nm之间时,器件的性能随着DLC厚度增加而变好;当DLC厚度为5.0nm时,器件具有最低的启动电压与最高的发光效率;当DLC厚度继续增加时,器件的性能随着DLC厚度增加而变差.并对ITO/MEH-PPV/DLC/Al和ITO/MEH-PPV/LiF/Al的器件性能进行了比较研究.     

KCl的纯度对OLED的影响

KCl作为阴极修饰层插入电子传输层和阴极之间,能提高所修饰器件的亮度.但KCl的纯度对器件的影响究竟有多大,本文进行了研究.选取纯度为99.99%、99.5%与混有一定杂质的KCl(经测试纯度为95.3%),制作ITO/NPB(40 nm)/Alq3(60 nm)/KCl(1 nm不同纯度)/Al结构的器件,并分别研究其亮度、电流密度和效率特性.发现随着KCl纯度的提高,器件的性能和电流密度有所提高.同时起亮电压降低.其中99.99%纯度的KCl所制备的器件性能最好,在16 V时最大亮度为7 585 cd/m2,在9.4 mA/cm2,时最大效率为2.4 od/A.由此可见,阴极修饰层的纯度对器件的性能有较大影响.使用高纯度阴极修饰材料,防止其被污染,是制备器件所要考虑的因素之一.     

L波段350W AlGaN/GaN HEMT器件研制

基于高纯半绝缘碳化硅衬底,采用金属有机化学气相沉积(MOCVD)工艺生长了AlGaN/GaN高电子迁移率晶体管(HEMT)外延材料.室温下霍尔测试结果表明,外延层二维电子气迁移率为1 950cm2/ (V·s),方块电阻为350 Ω,电阻均匀性为3％.通过优化工艺降低了欧姆接触电阻,提高了器件工作效率.采用源场板结合栅场板的双场板技术和增大源漏间距,提高了器件击穿电压.优化了背面减薄和背面通孔技术,提高了器件散热能力.采用阻抗匹配技术提升了芯片阻抗.最终采用预匹配技术和金属陶瓷封装技术成功制作50 mm栅宽的AlGaN/GaNHEMT器件.直流测试结果表明,器件击穿电压高达175 V.微波测试结果表明,在50 V工作电压、1.3 GHz下,器件输出功率达350 W,功率附加效率达81％,功率增益大于13 dB.     

High performance airbrush spray coated organic solar cells via tuning the surface tension and saturated vapor pressure of different ternary solvent systems

In this work, thieno [3,4-b] thiophene/benzodithiophene (PTB7): [6,6]-phenyl C71-butyric acid methyl ester (PC₇₁BM) based organic solar cell (OSC) with a new record of power conversion efficiency (PCE) of ∼7.62% has been realized using airbrush spray (AS) coating method in air ambient which can be well compatible with large-scale fabrication. By investigating the physical mechanism of AS coated blend films, a series of ternary solvent systems (TSS) are used to simultaneous optimize the surface tension and the saturated vapor pressure of solution. Therefore, different TSS further controls the morphology of PTB7:PC₇₁BM blend films precisely and systematically. It is elucidated that the chlorobenzene (CB)/o-Xylene (o-Xy)/1, 8-diiodoctane (DIO) TSS with a ratio of 37:60:3 vol.% could lead to a homogeneous surface morphology with a decreased aggregation domain size of active layer. In addition, the high fill factor, increased PC₇₁BM absorption and internal quantum efficiency indicate the formation of bicontinuous interpenetrating and fully percolated networks with nanostructured phase separation in BHJ blend films. Ultimately, the AS coated OSCs based on the TSS of CB/o-Xy/DIO gains a 34% enhancement in PCE, compared with the conventional CB/DIO solvent based OSCs.     

Solvent engineering of the electron transport layer using 1,8-diiodooctane for improving the performance of perovskite solar cells

In this work, the power conversion efficiency (PCE) of perovskite solar cells (PSCs) was improved by 14.8% (from 11.09% to 12.73%) by using 1,8-diiodooctane (DIO) as a solvent additive during the deposition of phenyl-C61-butyric acid methyl ester (PCBM) layers. The primary reasons for the PCE improvement are the simultaneous increases in the short-circuit current density, fill factor, and open-circuit voltage. The incorporation of DIO improves the morphology of the electron transport layer (PCBM), which plays an important role in charge dissociation, transportation, and collection. Our results indicate that engineering the morphology of the electron transport layer is a simple and effective method for developing high-performance PSCs.     

Impact of alkyl chain length of 1,n-diiodoalkanes on PC71BM distribution in both bulk and air surface of PTB7:PC71BM film

The impact of alkyl chain length of different additives, such as 1,4-diiodobutane (DIB), 1,6-diiodohexane (DIH), 1,8-diiodooctane (DIO) and 1,10-diiododecane (DID), on the PC₇₁BM distribution in PTB7:PC₇₁BM-based polymer solar cells, is systematically investigated, for the first time. Among these additives, DIO is found to have the optimum alkyl chain length that maximizes the performance of PTB7:PC₇₁BM based polymer solar cells, attaining a power conversion efficiency as high as 8.84%, which is almost four times higher than that without any additives. For DID additives (longer alkyl chain length than DIO), a drop in efficiency to 7.91% was observed. Experimental investigations show that the microstructure of the bulk and the surface layer as well as the surface morphology of the PTB7:PC₇₁BM polymer film can be controlled simultaneously by varying the alkyl chain length of additives. Results also show that the substantial improvement in performance is attributed to the improved 1) phase segregation, 2) PC₇₁BM distribution uniformity in the bulk of the PTB7:PC₇₁BM film, 3) surface smoothness and 4) high PTB7 content at the interface between the active layer and the top electrode.     

Two effects of 1,8-diiodooctane on PTB7-Th:PC71BM polymer solar cells

To obtain higher device performance, the ideal bulk heterojunction (BHJ) morphology should feature both nanophase separation to increase charge generation and bi-continuous percolating networks to increase charge transport. In this paper, solvent additive, 1,8-diiodooctane (DIO), was used in PTB7-Th:PC₇₁BM blend to improve BHJ morphology. The effect of DIO on charge generation and charge transport were studied carefully. Experimental study indicated that the effect of DIO on charge generation and charge transport are conflicted. Positive effects of DIO, which were induced by nanophase separation for charge generation in BHJ, are proved by the results of internal quantum efficiency (IQE) and photocurrent density (J_ph), and negative effects of DIO on charge transport has been investigated according to the time-of-flight secondary ion mass spectrometer (TOF-SIMS).     

Effect of the number of thiophene rings in polymers with 2,1,3-benzooxadiazole core on the photovoltaic properties

A series of polymers, poly{5,6-bis(decyloxy)-4-(thiophen-2-yl)benzo[c][1,2,5]oxadiazole} (1T-BO20), poly{4-(2,2′-bithiophen-5-yl)-5,6-bis(decyloxy)benzo[c][1,2,5]oxadiazole} (2T-BO20), poly{4-(2,2′-bithiophen-5-yl)-5,6-bis(decyloxy)-7-(thiophen-2-yl)benzo[c][1,2,5]oxadiazole} (3T-BO20) containing 2,1,3-benzooxadiazole derivative and different thiophene rings are synthesized. Effect of the number of thiophene rings on the optical, electrochemical and photovoltaic properties of the polymers is investigated. The maximum absorption wavelength and the optical band gap of the polymers are almost the same, indicating the polymers exhibit similar intramolecular charge transfer effect. The HOMO levels are in the order of 1T-BO20 (−5.60 eV) < 2T-BO20 (−5.45 eV) < 3T-BO20 (−5.36 eV), revealing that the HOMO level of the polymers are dependent of number of thiophene ring in the back bone. Under the illumination of AM 1.5G, 100 mW/cm², the power conversion efficiency (PCE) of PSCs based on these polymers increases in the order of 1T-BO20 (1.66%), 2T-BO20 (1.71%) and 3T-BO20 (1.92%). Besides, we find that the efficiency of PSCs showed very different responses by the addition of DIO as a processing additive. The devices based on 1T-BO20 and 2T-BO20 with DIO exhibit an enhancement of PCE from 1.66% to 3.65% and from 1.71% to 2.40%, respectively, whereas PCE of the device based on 3T-BO20 with DIO decreased from 1.92% to 1.76%.     

Efficient bulk heterojunction photovoltaic devices based on diketopyrrolopyrrole containing small molecule as donor and modified PCBM derivatives as electron acceptors

A new solution processable small molecule (DPP-CN) containing electron donor diketopyrrolopyrrole (DPP) core and cyanovinylene 4-nitrophenyl (CN) electron acceptor has synthesized for use as the donor material in the bulk heterojunction organic solar cells along with PCBM, modified PCBM i.e. F and A as electron acceptor. It showed a broad absorption in longer wavelength region having optical band gap around 1.64 eV. We have used PCBM, F and A as electron acceptor for the fabrication of bulk heterojunction photovoltaic devices. The power conversion efficiency (PCE) of the BHJ devices based on DPP-CN:PCBM, DPP-CN:F and DPP-CN:A blends cast from the THF solvent is 1.83%, 2.79% and 2.83%, respectively. The increase in the PCE based on F and A as electron acceptor is mainly due to the increase in both short circuit current (J_sc) and open circuit voltage (V_oc). The PCE value of the photovoltaic devices based on the blends DPP-CN:PCBM, DPP-CN:F and DDP-CN:A cast from the mixed solvents (DIO/THF) has been further improved up to 2.40%, 3.32% and 3.34%, respectively. This improvement is mainly due to the increased value of J_sc, which is attributed not only to the increase of crystallinity, but also to the morphological change in the film cast from mixed solvent. Finally, the device ITO/PEDOT:PSS/DPP-CN:A (DIO/THF cast)/TiO₂/Al device shows a PCE of 3.9%. The improved device performance could be attributed to the electron transporting and hole-blocking capabilities due to the introduced TiO₂ buffer layer.     

Synthesis and photophysical properties of semiconductor molecules D1-A-D2-A-D1-type structure based on derivatives of quinoxaline and dithienosilole for organics solar cells

A novel small molecule with D1-A-D2-A-D1 structure denoted as DTS(QxHT₂)₂ based on quinoxaline acceptor and dithienosilone donor units was synthesized and its optical and electrochemical properties were investigated. The thin film of DTS(QxHT₂)₂ showed a broad absorption profile covering the solar spectrum from 350 nm to 780 nm with an optical bandgap of 1.63 eV. The energy levels estimated from the cyclic voltammetry indicate that this small molecule is suitable as donor along with PC₇₁BM as acceptor for the fabrication solution processed bulk heterojunction solar cells for efficient exciton dissociation and high open circuit voltage. The organic solar cells based on optimized DTS(QxHT2)2:PC₇₁BM active layers processed with chloroform and DIO/CF showed overall power conversion efficiency of 3.16% and 6.30%, respectively. The higher power conversion efficiency of the solar cell based on the DIO/CF processed active layer is attributed to enhanced short circuit photocurrent and fill factor may be related to better phase separation between donor and acceptor in the active layer and more balanced charge transport, induced by the solvent additive. The power conversion efficiency of the organic solar cell was further improved up to 7.81% based on active layer processed with solvent additive, using CuSCN as hole transport layer instead of PEDOT:PSS and mainly attributed to increased fill factor and open circuit voltage due the formation of better Ohmic contact between the active layer and the CuSCN layer.     

Understanding How Processing Additives Tune the Nanoscale Morphology of High Efficiency Organic Photovoltaic Blends: From Casting Solution to Spun‐Cast Thin Film

Adding a small amount of a processing additive to the casting solution of photoactive organic blends has been demonstrated to be an effective method for achieving improved power conversion efficiency (PCE) in organic photovoltaics (OPVs). However, an understanding of the nano‐structural evolution occurring in the transformation from casting solution to thin photoactive films is still lacking. In this report, the effects of the processing additive diiodooctane (DIO) on the morphology of the established blend of PBDTTT‐C‐T polymer and the fullerene derivative PC₇₁BM used for OPVs are investigated, starting in the casting solution and tracing the effects in spun‐cast thin films by using neutron/X‐ray scattering, neutron reflectometry, and other characterization techniques. The results reveal that DIO has no observable effect on the structures of PBDTTT‐C‐T and PC₇₁BM in solution; however, in the spun‐cast films, it significantly promotes their molecular ordering and phase segregation, resulting in improved PCE. Thermodynamic analysis based on Flory‐Huggins theory provides a rationale for the effects of DIO on different characteristics of phase segregation due to changes in concentration resulting from evaporation of the solvent and additive during film formation. Such information may help improve the rational design of ternary blends to more consistently achieve improved PCE for OPVs.     

Manipulating the Crystallization Kinetics by Additive Engineering toward High-Efficient Photovoltaic Performance

Additive processing is proven to be an effective method to improve the efficiency and stability of perovskite solar cells; however, its intrinsic role in directing the crystallization pathway and thus morphology formation remains unknown. In situ grazing-incidence wide-angle x-ray scattering (GIWAXS) is applied to study the function of a 1,8-diiodooctane (DIO) additive in manipulating the crystallization behavior of perovskite thin films. It is seen that the DIO additive could induce multi-stage intermediate crystallization phases and increases the activation energy for nucleation and growth, which postpones the perovskite phase transformation time and broadens the transition zone. The elongated crystallization process affords improved perovskite thin film crystallinity and reduces defect density, which enables a longer carrier diffusion length. As a result, improved device efficiency, moisture, and thermal stability can be achieved. The current study provides a new prospective in understanding the additive function in perovskite thin film morphology control from fundamental parameters, indicating the importance of minor processing conditions in global property management toward high device performance.     

Synthesis and photovoltaic properties low bandgap D-A copolymers based on fluorinated thiadiazoloquinoxaline

In this communication, we report the design a low bandgap D-A copolymer consist of fluorinated thiadiazoloquinoxaline (TDQ) as strong acceptor and benzothiophene (BT), denoted as P(ffFlTDQ_x-BT) exhibit broad absorption profile covering from 350 nm to 1000 nm with optical bandgap of 1.26 eV. P(ffFlTDQ_x-BT) showed highest occupied molecular orbital (HOMO) energy level of −5.46 eV which is deeper than that for nonfluorinated counterpart copolymer. The photovoltaic properties were evaluated using conventional devices with a structure of ITO/PEDOT:PSS/P(ffFlTDQ_x-BT):PC₇₁BM/Al. After the optimizations of the P(ffFlTDQ_x-BT) to PC₇₁BM weight ratios, and concentration of the solvent additive (DIO), the devices showed overall power conversion efficiency of 7.27%. The higher value of PCE of this device is higher than that of nonfluorinated copolymer (5.80%) is attributed to the higher values of both J_sc and FF, related to the higher hole mobility and better exciton dissociation efficiency. Moreover, employing a low boiling point solvent additive, i.e. o-chlorobenzaldehyde (CBA) (boiling point 132 °C) for active layer deposition and after the optimization of concentration of CBA, the resulted PSC showed overall PCE of 8.10%, which is higher than the PSC based on active processed with DIO/CB, related to the better balanced charge transport, induced by the fast removal of residues of solvent. To our best of our knowledge, PCE of 8.10% is also the highest for the PSCs with low bandgap of below 1.30 eV.