有机光伏器件内部电场与性能关系及其调控研究

Organic photovoltaic (OPV) devices have been intensively investigated in the last a few years with very encouraging results. Recently reports from multiple groups have reached power conversion efficiencies (PCE) > 8%, and even >10%, which is considered a threshold for potential commercialization success. On the other hand, theoretical analysis reveals that the upper limit of OPV efficiency can be as high as 22-27%, thus there is still plenty of room for PCE improvement. A recent article on Adv. Mat.(2011) co-authored by the applicant demonstrated the concept of cathode interlayer in OPV. Incorporating a polyelectrolyte interlayer between the active layer and the Al cathode, the applicant and his coauthors showed that the open-circuit voltage, short-circuit current density and fill factor can be improved simultaneously. The key mechanism hypothesized in this article is that the electrical dipole moment of the interlayer produces an electrical field in alignment with the built-in field of the device, and consequently enhances charge carrier separation and transport. . In this project, we propose to investigate the detailed mechanisms how internal field in devices is controlled by interlayer and how internal field promote charge separation and transport. We will first obtain the cross-section of working devices and characterize the internal field using the scanning Kelvin probe microscopy. We will then use a series of molecules as interlayers to modify and tune the internal field. The modified devices will be characterized for photovoltaic performances and carrier transport details. Furthermore, we propose to construct a new field-effect OPV device, which utilize external gate voltage to control device internal field. We hope this new device concept will help to elucidate mechanisms through which device internal field enhances charge carrier transport, and also greatly improves OPV device efficiency.

近来有机太阳能电池研究取得了令人鼓舞的成果，多个研究组报导了>8%甚至>10%的效率，然而从热力学角度分析其理论极限可达22–27%，因此有机光伏器件的效率还有很大的提升空间。申请人与合作者2011年的Adv. Mat. 论文利用阴极界面中间层同时提升器件的Voc、Jsc、FF，成为本领域的一个突破和研究热点。该论文的核心思想是界面中间层的电偶极矩与内建电场叠加可以提升器件内部电场，促进工作状态下器件内载流子的分离和传输。. 本项目提出进一步研究界面中间层对器件内部电场的调控规律和内部电场提升器件性能的机理。首先我们将利用横切制样技术得到工作器件的横剖面，用电子显微镜和扫描光电探针技术原位表征器件内部微观结构和内部电场分布。同时，我们创新性地提出场效应增强有机光伏器件的概念，用外加门控电压调控器件内部电场以提升载流子分离、输运、收集效率，降低复合，从而提高有机光伏器件的光电转换效率。

光伏器件的内建电场是影响光生载流子的分离、复合、输运和收集等微观过程的重要因素之一，从而决定了器件性能。但长久以来缺乏对于器件内建电场的有效表征手段，特别是缺乏器件工况下的表征。我们利用横截面扫描凯尔文探针显微镜技术直观定量地测得工况下薄膜有机光伏器件的能级结构，进而分析和理解器件性能与器件内部电场的依赖关系。通过调控器件结构、界面中间层和活性层材料等，借助我们自主研发的偏压补偿法和去卷积法，定量地测得内建电势、开路电压和电极功函数差等重要参数，揭示了器件内部电场的影响因素，以及与器件性能的作用关系。基于对内部电场相关的微观机制的理解，我们提出利用外部电场调控内部电场的场效应增强有机光伏器件，并且看到了门电压调控之下器件性能的变化趋势。我们的技术解决了长期以来关于薄膜有机光伏器件内部电场的争议，而且该技术广泛适用于其他薄膜器件的研究，例如钙钛矿和量子点太阳能电池、发光二极管和薄膜晶体管等，有益于从微观角度探究器件工作机理指导器件性能优化，为将来大规模应用奠定坚实的基础。