采用新型电荷调制光谱与器件结构降低有机光伏的光电压损失

One of the biggest breakthroughs for organic photovoltaic (OPV) cells is the introduction of bulk-heterojunction (BHJ) structure that enables efficient charge generation in excitonic materials. However, BHJ also brings in an inevitable photo-voltage loss, which is defined as the “driving force” for exciton dissociation, bottlenecking the open-circuit voltage and PCE. Therefore, we find it challenging but significantly important to determine the correlation between the minimum-required “driving force” and the properties of the formed BHJ, and then to reduce the photo-voltage loss due to the excess “driving force”..Here we propose our solutions based on the study of both photo-physics and device fabrication. We will first invent a charge-modulated spectroscopy of “pump-push/probe” characteristics. Using this novel technique and photo-conductivity spectroscopy, we will testify and modify the existing models describing the “driving force”. Second, still using the invented technique, we will quantify the delocalization of each manifold of the charge-transfer states (CTS) of various BHJs, and to sort out the physical properties that lower the minimum required “driving force”. Finally, we introduce a BHJ structure targeting very low energetic disorder, highly delocalized CTS and negligible “driving force”. Such a structure would help to achieve low photo-voltage loss and high PCE..The successful execution of this project would not only provide a novel approach for the study of device physics, but also bring insight to the development of novel photovoltaic materials and device structures targeting low photo-voltage loss.

发展有机光伏过程中的里程碑之一是引入体异质结使光生激子能高效地转化为自由载流子。然而，随之引入的光生电荷“驱动力”明显限制了器件的开路电压和能量转换效率。因此，探究所需“驱动力”与异质结性质的关系，找到降低“驱动力”的方法是现阶段有重要意义的课题。.我们拟从器件物理和制备两方面展开研究。首先，开发一种新型的“激发-助推/探测”模式的电荷调制光谱，并结合光电导能谱完善现有的“驱动力”物理模型。随后，采用该新型的电荷调制光谱量化异制结界面处电荷转移态（和高阶振动态）波函数的离域度，并总结出有助于提高离域度、降低所需“驱动力”的异制结性质。最后，通过采用低能级无序度、高电荷转移态离域度的异制结结构制备器件，在低“驱动力”下实现光伏效应，从而降低光电压损失。.本项目的成功实施，不仅能提供一种全新的研究器件物理的测试方法，也能为减少有机光伏的光电压损失提供材料性质与器件构建方面的解决方案。

光生电荷“驱动力”被认为是有机光伏产生自由载流子的必要条件，但也导致了有机光伏额外的光电压损失、限制了器件性能。因此，采用合适的表征技术表征电荷转移态能量、研究驱动力大小，进而探究所需“驱动力”与异质结性质的关系具有重要的意义。.首先，有机光伏中体异质的电荷转移态能量（ECT）被视为有效带隙，是决定开路电压损失的重要参数。它与异质结光学带隙的差值被称为光生电荷驱动力。然而，在近年来非富勒烯受体成为主流的背景下，采用传统的线性吸收谱方法表征电荷转移态已无法提供可靠的结果。针对此问题，我们首先开发了基于电致吸收光谱技术的表征手段。我们采用此方法成功获得了了目前最为先进的体异质结体系PM6：Y6的ECT。该结果率先实现了对低驱动力体异质结体系ECT的可靠表征。在此基础上，研究也对电致吸收光谱的应用做了拓展。成功研究了器件的衰减机理、老化机理等问题。.其次，在可靠表征ECT的基础上，总结出有助于提高电荷转移态离域度、降低所需“驱动力”的异制结物理规律有重要的意义。通过分析以PM6：Y6为代表的电致吸收光谱的线形，总结出激子偶极特性与所需驱动力之间的关系。这一结果意味着基于非富勒烯窄带隙受体的有机光伏体系在充分提升受体材料激发态偶极矩变化的情况下能够是所需驱动力充分降低至0.13eV左右。.最后，本项目基于PM6：Y6体系，通过体异质结形貌工程实现了总复合损失低至0.43V，驱动力值低至0.14eV的有机光伏器件。相关参数得到了多重实验的独立验证，是目前有机光伏领域报道的最低能量损失之一。