基于聚合物光波导的电泵浦受激发射

Attributing to their low threshold of stimulated emission and high gain, semiconductive polymers are the potential materials promising as high gain media for solid-state laser devices. Meanwhile polymer can be fabricated to waveguide easily, which provide the possibility to realize facile waveguide. However, elctrically pumped organic laser is a very challenging problem for several reasons. First, it is difficult to pass very high current densities through most organic semiconductor. Second, there will be substantial optical losses associated with the contacts. Third,there is substantial absorption owing to the high density of injected charge carriers. Fourth,when opposite charges recombine in an organic semiconductor they frequently form a triplet exciton, which is not emissive in fluorescent materials and may also contribute to loss through its absorption. Finally, the singlet-triplet annihilation is a major barrier to electrically pumped lasing. . The aim of this proposal is to use semiconductive polymers as active layer to develop a kind of electrically pumped laser device with the distributed Bragg reflectors at the ends of waveguide. In this kind of device, two grating is used as resonator to reduce the threshould of pumping laser or injecting current. In this proposal, the work is mainly focused on following as several aspects: (1)basic photophysics in polymer waveguide under the presence of intense light and large injecting current, including spontaneous emission, dynamics of stimulated emission, dissociation of excitons under strong excitation, absorption of excited states, electric field effect on these processes and concerned parameters; (2) the design and fabrication of high gain waveguide based on semiconductive polymers, including the control of morphology of polymer waveguide, the approach to increase the gain of polymer waveguide, and the design of waveguide with multilayer structure; (3) the structure design and fabrication of electric pumped polymer laser devices with distributed Bragg reflectors, including choices of active polymers， electrode and modulation materials of electrodes, coupling between polymer active layer and modulation layer of electrode, the dependence of gain on the intensity of injecting and pump laser. Finally the techniques of fabrication and parameters of devices will be optimized to improve the performance of waveguide to achieve the demonstration of direct electrically pumped laser from polymer waveguide.

聚合物半导体是一种很好电致发光材料，且具有很好的激光增益特性。聚合物光波导增益区长，容易产生放大的放大的自发辐射（ASE），只要引入谐振光栅即可实现真正意义的激光。经过几年的研究，人们将这种结构器件的ASE阈值大幅度降低，这为实现电驱动下的ASE提供重要前提条件。本项目通过聚合物在高光强和高电流密度下光物理性质研究，澄清相关光物理过程，大幅降低光泵浦阈值光强。在此基础上通过聚合物分子排列控制，电极材料筛选，电极修饰等方法进一步降低有电极包裹的聚合物光波导的ASE的阈值光强；利用脉冲驱动减少器件热效应，提高器件电流和发光效率；通过染料掺杂和聚合物共混增加发射和吸收的能量间隔，减少基态和激发态吸收，提高ASE效率；通过电极外辅助层设计将电学设计和光学设计分别优化，在聚合物光波导上实现电驱动下ASE。本项目对澄清聚合物半导体高注入和高光强下的光物理过程，实现电泵浦聚合物激光具有重要促进意义。

本项目对聚合物放大自发辐射（ASE）和电致发光做了一些研究，同时也对新型的有机-无机复合钙钛矿的ASE做了一些研究。我们利用激光光刻技术，制备了分布反馈结构的光波导，ASE性能得到优化。ASE半高全宽从9.7nm下降到了4.2nm，ASE阈值从518nJ/pulse下降到297nJ/pulse。利用F8BT:P3HT共混材料降低了ASE阈值，提高了载流子迁移率，电流密度提高了一个数量级。不同P3HT比例的共混聚合物薄膜的受激辐射特性研究显示，当P3HT的质量比小于20%时, 共混物光波导的ASE阈值随着P3HT比例增加而下降，并在P3HT比例约为15%到20%时阈值最低。F8BT薄膜和P3HT含量为20%的共混薄膜受激辐射特性随温度变化研究显示，温度降低可显著降低F8BT:P3HT共混薄膜ASE的阈值光强。用F8BT:P3HT制备了以活泼金属为阴极的电致发光器件，测量了不同P3HT比例的器件的电流以及发光特性，P3HT含量约20％的器件具有较高的亮度，但P3HT含量约为10％的器件具有较高的效率。此外，利用电脉冲驱动的方式测量了F8BT:P3HT共混聚合物电致发光器件的瞬态发光特性，脉冲驱动电流密度可以提高一个数量级，但在高密度激发下，同样发光效率下降较多。有机材料载流子迁移率很低，并且折射率比较低，这使得聚合物光波导的电泵ASE的困难，我们对有机-无机复合钙钛矿材料的ASE做了一些研究和探讨。通过混合溶剂制备了超平有机-无机复合钙钛矿薄膜，利用真空热处理显著改善钙钛矿薄膜的结晶状态，发现钙钛矿ASE温度特性，探索了实现电泵浦ASE的可能途径。