Controlling internal and external interfaces in 2D perovskites to overcome intrinsic anisotropy of charge transport in solar cells

Köhler-Thelakkat 联合项目重点研究如何通过修改内部界面来控制和操纵钙钛矿的维度，以及如何通过修改外部钙钛矿-空穴-传输层界面来提取电荷。目的是获得环境稳定且向电极表现出改进的垂直电荷传输的太阳能电池。在第一部分中，我们解决了二维钙钛矿中电荷传输的各向异性问题，因为这些高度稳定的层状材料由于隔离的有机夹层而遭受较差的垂直电荷传输。为了克服有机层缺乏电荷渗透的问题，我们将合成并掺入属于二酮吡咯并吡咯（DPP）类的有机半导体铵阳离子，它们适合二维层状钙钛矿晶体结构，从而有助于电荷传输和吸收。特别地，这些DPP铵阳离子的分子能级和HOMO-LUMO间隙将相对于无机层的带隙进行调整。这样，我们就可以解决电子活性有机层如何改变量子阱结构，从而改变吸收和随后的能量或电荷转移的基本问题。在第二部分中，我们解决有关钙钛矿和p型提取层之间的外部界面的问题。在这里，我们设想通过多种直接氧化还原掺杂剂和空穴导体的共蒸发来合成新型掺杂的p型引出层，以控制掺杂程度，避免不确定的空气氧化并保证掺杂剂在空穴导体中的均匀分布。这可以促进使用较少量的掺杂剂和具有改善的电荷提取的限定界面。良好控制的无溶剂 p 型层制备也有助于研究这种掺杂半导体材料的光谱特征和能量随掺杂程度的变化。我们研究了掺杂剂是否影响 DOS 宽度、陷阱填充、费米能量形成、电荷传输（赝渗透）的性质以及由此产生的载流子迁移率。新型 2D 钙钛矿和 p 型层都将被纳入太阳能电池的 p-i-n 结构中，以评估和理解我们创新方法的含义。光物理学解决了有机层和无机层之间激发能的相互作用以及最终太阳能电池器件中电荷传输和电荷提取的协同作用。我们询问掺杂 p 型层改善的电荷提取是否确实减少了 2D 钙钛矿薄膜中的复合，从而提高了器件效率，以及这些新型 2D 钙钛矿材料是否提高了器件寿命。

The joint project Köhler-Thelakkat focusses on the question of how to control and manipulate the dimensionality of perovskites by modification of the internal interfaces as well as the extraction of charges through modification of the external perovskite-hole-transport layer interface. The aim is to obtain solar cells that are environmentally stable and exhibit improved vertical charge transport towards the electrodes.In the first part, we address the issue of anisotropy of charge transport in 2D perovskites, since these highly stable layered materials suffer from poor vertical charge transport due to isolating organic interlayers. To overcome the lack of charge percolation through the organic layers, we will synthesize and incorporate organic semiconductor ammonium cations belonging to the class of diketopyrrolopyrroles (DPPs) that fit within the 2D layered perovskite crystalline structure and thus contribute to charge transport and absorption. Particularly the molecular energy levels and HOMO-LUMO gap of these DPP ammonium cations will be tailored relative to the band gap of the inorganic layer. With this, we can address the fundamental question how the electronically active organic layer modifies the quantum well structure, and thus absorption and subsequent energy or charge transfer. In the second part, we address the issues concerning the external interface between perovskite and the p-type extraction layer. Here we envisage the synthesis of novel doped p-type extraction layers by co-evaporation of diverse direct redox dopants and hole conductors in order to control the degree of doping, to avoid uncertain air-oxidation and to guarantee uniform distribution of dopants in hole conductor. This can facilitate the use of less amounts of dopants and a defined interface with improved charge extraction. A well-controlled solvent-free preparation of p-type layers also facilitates the study of spectroscopic features and energetics of such a doped semiconductor material as a function of the degree of doping. We investigate whether the dopants impact on the width of the DOS, trap-filling, Fermi-energy formation, the nature of charge transport (pseudo-percolation) and the resulting charge carrier mobility.Both the novel 2D perovskites and p-type layers will be incorporated in a p-i-n structure of solar cell to evaluate and understand the implications of our innovative approach. The photophysics addresses interactions of excitation energies between organic and inorganic layers as well as the synergy of charge transport and charge extraction in final solar cell devices. We ask whether improved charge extraction by the doped p-type layer indeed reduces recombination in the 2D perovskite film, thus increasing device efficiency, and whether these novel 2D perovskite material improves the device lifetime.