Entropic Stabilization of Hybrid Perovskites

在过去的十年里，混合钙钛矿已经彻底改变了太阳能研究。像MAPI （CH3NH3PbI3）这样的材料可以作为吸收剂，也可以在很远的距离上分离电荷，因此功率转换效率提高了20%以上。困扰研究人员的一个问题是，在存在水的情况下，材料会通过甲基铵质子的转移而降解。目前存在的抑制这些影响的方法包括在A位点的质子的PKa工程，以及用无机离子（如Cs+）代替有机离子。然而，这些材料仍然表现出不同程度的不稳定性。然而，最近出现了一种新的范式，它挑战了传统的晶体固体图景，即高熵材料的概念。这些材料与传统材料非常不同，因为它们利用增加的无序性来最小化自由能。简单地说，这是通过在晶态的阳离子或阴离子亚晶格中加入等量的各种元素来实现的，以最大化熵混合项，从而最小化固体的自由能。现在有许多材料用这种方法稳定下来，包括金属、金属氧化物、金属硫化物和氧化硫化物。在这个博士课程中，我们将测试使用这种方法可以赋予混合钙钛矿稳定化的假设。我们将通过自旋镀膜和CVD制备这些新材料的薄膜，并使用最新的operando XPS技术测试它们对水的稳定性。预计将建立一种稳定杂化钙钛矿材料的新范式。

Hybrid perovskites have revolutionized solar research in the past decade. Materials such as MAPI (CH3NH3PbI3) can act as absorber and is also able to separate charge over large distances, and power conversion efficiencies have risen beyond 20% as a result of this. One of the concerns that has troubled researchers is the degradation of the materials in the presence of water via transfer of the methylammonium proton. Approaches that currently exist to depress these effects include the engineering of PKa of the proton at the A site, as well as the replacement of the organic ion with an inorganic ion e.g. Cs+. However, the materials still show varying amounts of instability. However, recently a new paradigm has emerged that has defied the traditional picture of crystalline solids, which is the notion of high entropy materials.These are very different to traditional materials because they utilise increased disorder to minimise their free energy. In simple terms, this is achieved by adding various elements in equivalent amounts to either the cationic or anionic sublattices in the crystalline state to maximise the entropic mixing term, which in turn minimises the free energy of the solid. There are now a number of materials stabilised in this way including metals, metal oxides and metal sulfides and oxysulfides. In this PhD programme we will test the hypothesis that stabilization can be conferred on hybrid perovskites using this approach. We will make thin films of these new materials by both spin coating and CVD, and test their stability vs water using the latest operando XPS techniques. It is envisaged that a new paradigm for stabilization of hybrid perovskite materials will be established.