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

Köhler-Thelakkat联合项目的重点是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。在第一部分中，我们解决了2D钙钛矿材料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了有机夹层而遭受着较差的垂直电荷传输。为了克服通过有机层的电荷渗透不足的问题，我们将合成并结合属于二酮基吡咯(DPP)类的有机半导体氨阳离子，这些阳离子适合于2D层状钙钛矿晶体结构，从而有助于电荷的传输和吸收。特别是，这些DPP铵离子的分子能级和HOMO-LUMO带隙将相对于无机层的带隙进行调整。有了这一点，我们就可以解决基本的问题，即电子活性有机层如何改变量子阱结构，从而吸收和随后的能量或电荷转移。在第二部分中，我们讨论了钙钛矿和p型萃取层之间的外部界面问题。在这里，我们设想通过不同的直接氧化还原掺杂剂和空穴导体的共蒸发来合成新型的掺杂p型萃取层，以控制掺杂程度，避免不确定的空气氧化，并保证掺杂在空穴导体中的均匀分布。这可以促进使用更少的掺杂剂和定义的界面，并改进电荷提取。良好控制的p型层的无溶剂制备也有助于研究这种掺杂半导体材料的光谱特性和能量学随掺杂程度的变化。我们研究了掺杂是否影响DOS的宽度、陷阱填充、费米能量的形成、电荷传输(伪渗流)的性质以及由此产生的电荷载流子迁移率。我们将在p-i-n结构的太阳能电池中加入新型的2D钙钛矿和p型层来评估和理解我们的创新方法的含义。光物理涉及有机和无机层之间的激发能量的相互作用，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。我们问，通过掺杂p型层改进的电荷提取是否真的减少了2D钙钛矿薄膜中的复合，从而提高了器件效率，以及这些新型的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.