Exploration of novel concepts for organic photovoltaics

在有机太阳能电池中，入射光子在光敏材料中产生局域激发态，激子可以被视为准粒子。为了转换成光电流，这些激子需要迁移到两种材料之间形成的界面，在那里它们被解离。通常，激子扩散长度（激子在材料内可以行进多远的量度）不能匹配完全收集太阳能所需的光吸收长度。因此，活性材料通常是薄的并且不是完全吸收层。由于掺入的电子的不同自旋构型，激发的分子状态可以是单重态或三重态。传统的有机材料是荧光材料，其中单重态激子被光子激发。因为到三重态的相互转换通常以小速率发生，所以太阳能电池中的激子迁移通常经由单线态激子扩散介导。另一方面，三重态的寿命更长，因为它们的失活是量子力学禁止的。迄今为止，已经研究了能够有效地将单重态转化为三重态的材料，然而，状态之间的能量分裂很大，并且不利于在有机太阳能电池中的应用。本申请集中于探索能够有效地将单重态转化为三重态的新型光活性材料。因此，这些三重态将能够在层内进一步迁移，从而实现更高的外部量子效率。同样重要的是，为了克服系统间交叉步骤期间的能量损失，将研究由于单重态和三重态之间的小能量差而显示出高系统间交叉的材料。预期包含所提出的材料的太阳能电池显示出功率转换效率的显著提高。

In organic solar cells, the incoming photons generate localized excited states in the photoactive materials the excitons that can be seen as quasiparticle. In order to be converted into photocurrent, these excitons need to migrate to an interface formed between two materials where they are dissociated. Often, the exciton diffusion length a measure how far an exciton can travel within the material cannot match the optical absorption length needed to fully harvest the solar power. As a consequence, the active materials typically are thin and not completely absorptive layers.As a result of different spin configurations of the incorporated electrons, excited molecular states can either be singlet or triplet states. Conventional organic materials are fluorescent materials, where singlet excitons are excited by photons. Because interconversion to the triplet state typically happens with small rates, exciton migration in solar cells is typically mediated via singlet exciton diffusion. On the other hand, triplet states are much longer-lived because their deactivation is quantum mechanically forbidden. To date, materials have been investigated that efficiently channel singlets to triplets, however the energetic splitting between the states is large and detrimental for application in organic solar cells.This application focuses on the exploration of novel photoactive materials, which are able to efficiently convert singlets into triplets. As a consequence, these triplets will be able to migrate further within the layers, enabling higher external quantum efficiencies. Equally important, in order to overcome the energy loss during the intersystem crossing step, materials will be investigated that show a high intersystem crossing as a result of small energy differences between singlet and triplet states. Solar cells comprising the proposed materials are expected to show a noticeable increase in power conversion efficiency.