基于陷光ZnO电子传输层的倒结构有机太阳电池的研究

Organic solar cells (OSCs) are attractive because the lightweight and the advantage of low fabrication-cost and compatible with the flexible substrate. However, the enhancement of light absorption by light-trapping is needed for the thickness of photoactive layer is limited by the short diffusion length of an exciton and the low mobility of carriers. It is the urgent problem to fully absorb the light by the limited thickness of the active layer for improving power conversion efficiency. Introducing the light-trapping structure, which can effectively improve the light absorption. But inferior interface contact quality between the inorganic electron transport layer and organic active layer leads to poor electron extraction, which imposing a restriction on further improving the performance of OSCs. To resolve this issue and achieve higher efficiencies, a ZnO thin film with light-trapping structure has been introduced as the electron transport layer. By using the ZnO nanostructures in combination with the back reflection electrode, the light absorption could be increased through the light scattering and multiple reflections to increase light optical path in the active layer. Meanwhile, an interfacial layer has been introduced to improve the contact quality and electron extraction. Which can increase the open circuit voltage and fill factor simultaneously, and realize the device efficiency effectively improved. Our project will make a profound theoretical analysis and detailed experimental research on light-trapping and photocarrier transportation mechanisms of OSCs. Which has important scientific significance, and provides a promising way for efficiency enhancement of OSCs.

有机太阳电池质量轻，成本低与柔性衬底兼容，受到广泛关注。但是，由于有机材料中光生激子扩散长度短，载流子迁移率低，限制了光活性层的厚度。因此以活性层有限的厚度实现对光的充分吸收，提高电池效率，是目前该领域急需解决的问题。引入陷光结构，可有效提高光吸收率。但是由于活性层与电子传输层表面能不同，差的接触质量给电池中载流子输运、电极对电荷的选择及收集造成很大的损失，电池性能仍难以提升。项目申请人提出采用带有陷光纳米结构ZnO作为电子传输层，利用其纳米结构的散光性能，结合电池背反射电极，通过光的散射、多重反射增加光在活性层中的光程，增加光吸收；同时引入修饰层，优化与活性层的接触界面。使电池的开路电压、填充因子均有效提高，实现电池效率的大幅提升。本项目对有机电池中陷光和载流子输运机制的理论分析和实验研究，不仅具有重大科学意义，更有望为有机电池性能提高、加快商业化生产应用提供一条新的途径。

本项目研究陷光ZnO薄膜电子传输层对提高倒结构有机太阳电池效率的影响。主要工作：一、陷光ZnO研究：发现Mg掺杂可提高ZnO 纳米柱薄膜300-430nm波段的光散射能力；利用种子层退火处理，可实现ZnO纳米柱薄膜300-850nm宽光谱散射能力可控；两步退火处理获得电导率为2.76E-03S/cm同时具备光散射能力的Al掺杂ZnO薄膜，RMS=21.68nm，300nm-500nm波段平均Haze=9.88%。为制备光散射可调控的ZnO电子传输层做好了重要准备工作。二、基于陷光ZnO的倒结构有机电池：基于平面ZnO的电池器件获得光电转化效率2.65%，基于陷光AZO的P3HT:PCBM器件效率达到3.79%。一方面Al掺杂提高了ZnO电子传输层的电学性能，增强的电导率降低了表面接触阻抗，减少了载流子复合;另一方面，通过增加光程实现有效的陷光，增强活性层的光吸收；同时增大了与活性层的接触界面，获得陷光和载流子传输特性之间的平衡，因此大幅度提高电池性能。为进一步确认陷光AZO的光散射效果，我们将其应用在PTB7:PC71BM体系中：相比平面ZnO电池，基于陷光AZO的PTB7: PC71BM器件效率从4.28%提高到6.15%，源于增强的Jsc(14.77&16.33mA/cm2)和FF(49.3%&56.1%)。虽然与国际最先进电池存在差距，但增强的Jsc (P3HT器件9.13-11.12mA/cm2；PTB7器件14.77-16.33mA/cm2)充分证明陷光AZO电子传输层能提供真正的光吸收增强并且与BHJ形成良好的接触。这个简单有效的陷光方法适用于其他薄膜太阳电池。三、银纳米线（AgNWs）透明导电薄膜的光散射研究：利用透射率计算AgNWs折射率，发现长AgNWs消光系数随波长先降后增的趋势；对不同长度AgNWs光学性能研究，定义了AgNWs反射方向的散射，受其网格尺寸控制，对于AgNWs的应用具有重要意义；AgNWs光散射可控研究，为其在薄膜太阳电池的应用提供了重要参考价值。项目资助发表SCI论文九篇，获得国家发明专利授权8项，待发表论文三篇，培养在读硕士研究生2名。项目投入直接经费20万元，支出14.5301万元，各项支出与预算相符；剩余5.4699万元，计划用于项目研究后续支出。