Optical, Electrical and Magnetic Studies of pi-Conjugated Polymer/Organic Acceptor Blends for Photovoltaic Applications

技术支持：该项目旨在更好地理解PCP（p-共轭聚合物）与用于体异质结OPV（有机光伏）器件的分子受体的共混物中的电子态，电荷传输和自旋现象。在共混物（薄膜和器件）中研究的过程/现象包括：超快激子解离，电荷产生机制，带隙下响应，PCP链和受体分子的电荷转移复合物（CTC）的形成，成对复合，自旋相关的传输和复合，以及形态相关的载流子迁移率。这些研究将在不同浓度的PCP-富勒烯混合物中进行，这些混合物显示出高的OPV效率，以及在以前没有使用过的新型PCP-受体混合物中进行。预计结果将有助于基本了解控制OPV器件光伏响应的物理过程，并有可能将其太阳能转换效率提高到目前的6%以上。该方法利用光学、电学和磁学实验技术：（i）在0.1至2.5 eV的光谱范围内，使用泵浦/探测光调制（PM）技术研究共混物中的超快激子和极化子动力学;（ii）第（i）款的激发须在以下时间由高至低变动─间隙光子能量，以探索极化子产生的可能性，而不是传统的电荷从聚合物链转移到受体分子上的过程;（iii）共混物中CTC态的可能形成将通过IR-光致发光、带隙下吸收、IR-电吸收和光生极化子作用光谱来研究;（iv）用于获得载流子迁移率的电导纳光谱;（v）用于研究极化子复合的OPV器件的磁阻测量;以及（vi）用于研究自旋相关复合的自旋1/2极化子的光学检测磁共振的动力学，以及OPV器件中的自旋-晶格弛豫速率。非技术性：该项目涉及电子/光子材料科学领域的基础研究问题，具有高度的技术相关性。这些研究可能会导致OPV（有机光伏）器件与提高太阳能转换效率，并加深我们对PCP受体共混物的理解。此外，实验工作的整合，包括聚合物和小分子合成，光学，磁输运，建模和设备制造，加工和测试，将有助于教育研究生和本科生，以及博士后助理谁将参与这个跨学科的研究项目。研究生课程？有机光电子学：基础研究与器件应用？也在计划中。一个推广计划包括高中生及其教师导师在夏季参与研究，以及向公众展示有机发光二极管和OPV器件的工程演示。

Technical: This project aims for greater understanding of electronic states, charge transport, and spin phenomena in blends of PCP (p-conjugated polymers) with molecular acceptors that are used in bulk-heterojunction OPV (organic photovoltaic) devices. Processes/phenomena to be investigated in blends (films and devices) include: ultrafast exciton dissociation, charge generation mechanism, below-gap response, formation of charge transfer complex (CTC) of PCP chains and acceptor molecules, geminate recombination, spin-dependent transport and recombination, and morphology-dependent carrier mobility. These studies will be conducted in PCP-fullerene blends of different concentrations that show high OPV efficiency, as well as in novel PCP-acceptor blends that have not been used before. Outcomes are expected to contribute to basic understanding of physical processes that govern photovoltaic response in OPV devices, and have potential to increase their solar power conversion efficiency beyond the 6% record of the present time. The approach utilizes optical, electrical and magnetic experimental techniques: (i) ultrafast exciton and polaron dynamics in the blends will be investigated using a pump/probe photomodulation (PM) technique in the spectral range of 0.1 to 2.5 eV; (ii) the excitation in (i) is to vary from above to below-gap photon energy to explore the possibility of polaron generation by processes other than traditional charge transfer from the polymer chain onto the acceptor molecule; (iii) the possible formation of a CTC state in the blends will be studied by IR-photoluminescence, below-gap absorption, IR-electroabsorption, and photogenerated polaron action spectra; (iv) electrical admittance spectroscopy for obtaining the carrier mobilities; (v) magnetoresistance measurements of OPV devices for studying polaron recombination; and (vi) dynamics of optically-detected magnetic-resonance of spin ½ polarons for studying spin-dependent recombination, and spin-lattice relaxation rate in OPV devices. Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. These studies may lead to OPV (organic photovoltaic) devices with enhanced solar power conversion efficiency, and deepen our understanding of the PCP-acceptor blends. In addition, the integration of experimental efforts, including polymer and small molecule synthesis, optics, magneto-transport, modeling, and device fabrication, processing and testing, will serve to educate graduate and undergraduate students, and a postdoctoral associate who will be involved in this interdisciplinary research project. A graduate course on ?Organic optoelectronics; basic studies and device applications? is also planned. An outreach program includes research participation of high school students and their teacher mentors during the summer, as well as engineering demonstrations for illustrating organic light emitting diodes and OPV devices to the public.