有机光伏活性层材料中电子和空穴之间的结合能较大，使光生电子和空穴被束缚以激子的形式存在，激子需要先扩散到给体和受体的界面，之后经由界面解离才能转换为自由电子和空穴。通常在该过程中伴随激子的复合损失，造成电池效率的降低，当活性层厚度增加之后该复合损失更为严重。因此，改善激子复合对于提高电池效率非常关键。活性层中给体和受体的结晶堆积和界面分布是影响激子扩散和解离的直接因素，改善结晶堆积质量有利于提高激子扩散距离，降低传输扩散中的复合损失，而增加给受体界面则可以提高激子解离效率，降低界面处的复合损失。在此，针对有机太阳能电池中的激子复合损失问题，本文将从提高活性层材料结晶堆积质量，增加激子解离界面等方面展开研究，以提高电池效率，主要包括以下内容：

一、从改善结晶堆积质量的角度出发，设计了一系列固体添加剂用于调控活性层的聚集和结晶行为，添加剂通过与受体分子之间的相互作用，诱导受体分子聚集，进而调控其结晶行为。分子堆积更加紧密有序，活性层的结晶质量有效改善，激子扩散中的复合损失降低，有效传输距离变长。同时活性层在垂直方向上的结晶排布更加均匀有序，有利于垂直方向上的电荷传输。最后，复合损失得到有效抑制，器件效率显著提高。此外，添加剂展现出良好的普适性，在多种活性层体系中实现器件效率提升，器件最高可以实现19.3%的光电转换效率。

二、从增加激子界面解离效率的角度出发，制备了准平面异质结和体异质结共存的新型buried-BHJ结构，实现了有效的激子解离和电荷收集。该结构在垂直方向上具有准平面异质结的给受体组分分布特点，提供电荷向两电极的传输通道，同时在给体和受体相中还埋入了大量给体/受体接触界面用来实现激子有效解离。与传统的准平面异质结和体异质结相比，buried-BHJ结构可同时满足高效的激子解离和电荷传输，从而降低复合损失。此外，buried-BHJ结构具有更好的膜厚容忍度，当活性层厚度达到500 nm时，器件仍然能保持16.0%的光电转换效率。

In organic solar cells (OSCs), the photogenerated electrons and holes are generally bound as localized excitons because of the large binding energy of organic semiconductors. The excitons need to diffuse to the interface of the donor and acceptor for dissociation. Extra recombination losses would be suffered during the diffusion and dissociation processes, resulting in a decrease in the device efficiency. This recombination loss is more serious with increasing the thickness of active layers. Therefore, to improve the efficiency, the recombination losses have to be mitigated. The crystallization and interface distribution of the donor and acceptor in films directly affect exciton diffusion and dissociation. Improving the crystallization is conducive to increasing the exciton diffusion distance and reducing the recombination loss during the transport and diffusion process, while increasing the donor and acceptor interface is favorable to improving the exciton dissociation efficiency and reducing the recombination loss at the interface. In addressing the issue of exciton recombination losses in OSCs, this study focuses on improving the crystallization quality of the active layer materials and increasing exciton dissociation interfaces to enhance OSC efficiency. These include the following aspects:

1. A series of solid additives are designed to regulate the aggregation and crystallization behavior of the active layer. The additives can induce the aggregation of the acceptor molecules due to molecular interaction, and then regulate the crystallization behavior. The ordered molecular stacking improves the crystalline quality of the active layer, reducing recombination losses during exciton diffusion and effectively lengthening the transport distance. Simultaneously, the vertical distribution of crystallization in the active layer becomes more uniform and ordered, facilitating charge transfer in the vertical direction. Finally, recombination losses are effectively suppressed, resulting in a significant improvement in device efficiency. Furthermore, the additives exhibit good universality, achieving efficiency enhancements in various active layers. A power conversion efficiency (PCE) of 19.3% is achieved.

2. A novel buried-heterojunction (buried-BHJ) structure with pseudo-planar heterojunctions and bulk heterojunctions coexisting was fabricated to achieve effective exciton dissociation and charge transport, simultaneously. This structure exhibits pseudo-planar heterojunction characteristics in the vertical direction, providing transport channels for charges to both electrodes. Additionally, a large number of BHJ interfaces exist within the donor or acceptor domains to ensure effective exciton dissociation. Compared to traditional pseudo-planar heterojunctions and bulk heterojunctions, the buried-BHJ structure can simultaneously achieve efficient exciton dissociation and charge transport, thereby reducing recombination losses. Moreover, the buried-BHJ structure exhibits decent thickness tolerance, maintaining a PCE of 16.0% even when the active layer thickness is 500 nm.