应用于光伏元件的刚性-柔性聚烷基噻吩嵌段共聚物的化学结构及其自组装形态控制

Optimization of organic photovoltaics devices relies on controlling the nanoscale morphology of at least two semiconducting materials with different energy level alignments to maximize charge separation, recombination, and transfer. Since Voc of PSC is directly proportional to the difference between HOMO level of the electron donor and LUMO level of the electron acceptor, to improve Voc by using deeper HOMO level electron donor is an effective approach to getting high power conversion efficiency. As active layer materials , poly(3-alkylthiophene)s are very important, in which substituents are generally used as fine-tuning methods to tweak the physical properties of conjugated polymers, particularly the electronic properties(energy levels, band gap, mobility, etc.). Because of the chemical incompatibility between the two blocks, the block copolymers containing P3AT microphase separate into equilibrium ordered heterojunction structures. Self-assembly alone creates interfaces on the 10 nm length scale and is an exciting platform from which to understand the fundamental role of patterning on device performance, particularly charge separation and recombination events. . In this study, we focus on the synthesis, self assembly and utilization of rod -coil block copolymer containing P3AT for solar cell energy conversion and elucidate the correlations between morphologies and photovoltaic properties of rod-coil block..Firstly, a new P3AT derivative is designed and prepared by tuning the number of electron donating groups, the alkyl side chains, and the HOMO level of P3ATs are intended to reduced to ~-5.4 eV, without changing their optical band gap. .Secondly, a series of rod -coil block copolymers containing P3AT are synthesized through the use of controlled Grignard metathesis (GRIM) polymerization method and subsequent atom transfer radical polymerization (ATRP). The GIRM enables the block ratios to be controlled by the mole ratios of respective monomers, which overtake a major difficulty in experimentally addressing conjugated rod-coil block copolymer self-assembly. Herein, conjugated rod-coil block copolymers are parametrized by φ, ν, χN, μN, and ratios of the last two parameters. We study the influence of these parameters on the morphologies of the self assembly and intend to obtain the ideal microphase structure, as the case of perpendicular lamellae corresponds to the situation in which the confining surfaces had no preferential interactions with either of the polymers.. Thirdly, we use morphologies generated from different self assembly behavior of rod-coil block copolymers to study their device characteristics. The device characteristics employing donor -acceptor materials of rod-coil block copolymers involve a complex interplay of several features including the orientation of domains, domain widths, the degree of phase separation, and the orientation of rodlike domain molecules in influencing the PV characteristics of the device.

利用GRIM反应制备高规整度P3AT，其半活性机理可将P3AT末端功能化，结合ATRP 反应接入柔性嵌段，可制备分子量及其分布可控的Rod-coil嵌段共聚物，为研究嵌段共聚物自组装相分离特性提供结构可控的模型共聚物。通过改变烷基结构和数目，调整聚合物能带隙和HOMO能级；研究Flory-Huggins参数、体积分数、Maier-Saupe参数及柔性与刚性嵌段比和相分离形貌的关系，并结合工艺条件（溶液参数、涂层厚度以及退火处理等），调整嵌段共聚物的结构，实现对晶相大小、形态以及取向的可控的设计，制备具有垂直纳米阵列排列的理想相分离结构的嵌段共聚物。最后，将组成的有序纳米结构作为形成本体异质结结构的模版，除去柔性相后的空白处填充受体材料，将该复合材料组装成为太阳能光伏装置，进一步研究自组装相分离结构与其光电性能的关系，建立一套关于嵌段聚合物自组装所形成的杂化结对光物理性能影响规律的基础理论。

本研究通过聚烷基噻吩的格式置换（GRIM）反应，制备了P3HT-PLA嵌段共聚物。该聚合物可自组装成周期性、有序、微相分离结构。这种可控的形貌是优化光伏电池电荷分离，是提高电荷传输的重要方法。通过控制嵌段聚合物的化学结构、嵌段链长，使其相区宽度与对应的聚合物嵌段链长接近，结构接近理想本体异质结结构。实验表明，通过主要参数的调节，如：嵌段共聚物体系中组分的体积分数fA、两组分之间的Flory-Huggings相互作用参数（χAB）、共聚物各个嵌段的聚合度之和（N）、Maier-Saupe 刚性段相互作用强度µN以及几何不对称参数v，调控嵌段共聚物聚三己基噻吩-聚乳酸（P3HT-PLA）的嵌段共聚物的结构，进而调控嵌段共聚物的体系的自组装形态， 得到理想的相分离结构。这种相分离导致的大面积的、纳米尺寸的电子供体-受体界面，其相区尺寸与激子运动距离（~10nm）接近，从而保证大多数的激子在复合淬灭前扩散到电子供体-受体界面，形成在相分离的共混层中各自扩展延伸或相互穿越的互传网络结构，以使解离的激子,空穴、电子可以各自经由这些互传网络传输到相应电极。.另外，本研究开展了以高规整聚3-己基噻吩（rr-P3HT） 作为电子给体材料，硫化镉（CdS）无机半导体作为电子受体材料，并引入具有良好电导率的石墨烯片层作为电子的导体材料，将rr-P3HT以共价键的形式接枝到氧化石墨烯（GO）上，得到GO-rr-P3HT接枝材料，然后将CdS原位合成负载在GO-rr-P3HT接枝材料，最终得到GO-rr-P3HT-CdS三元异质结材料，不仅综合了GO、rr-P3HT、CdS三种材料优异的光电性能，还通过rr-P3HT的接枝及CdS的原位负载有效的提高了GO-rr-P3HT-CdS三元异质结材料的光生空穴电子的传输能力，减少了空穴电子复合的概率，大大提高了其光电转化性能，具有深远的研究意义。