Entropic Stabilization of Hybrid Perovskites

混合钙钛矿在过去十年中彻底改变了太阳能研究。诸如CH3NH3PbI3的材料可以作为吸收剂，并且还能够在长距离上分离电荷，并且因此功率转换效率已经上升超过20%。困扰研究人员的一个问题是，在水的存在下，通过甲基铵质子的转移，材料会发生降解。目前存在的抑制这些效应的方法包括在A位点改造质子的PKa，以及用无机离子例如Cs+替换有机离子。然而，这些材料仍然显示出不同程度的不稳定性。然而，最近出现了一种新的范式，它挑战了晶体固体的传统图景，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来最小化它们的自由能。简而言之，这是通过将等量的各种元素添加到结晶状态下的阳离子或阴离子亚晶格中以使熵混合项最大化，从而使固体的自由能最小化来实现的。现在有许多以这种方式稳定的材料，包括金属、金属氧化物和金属硫化物和氧硫化物。在这个博士课程中，我们将测试使用这种方法可以在混合钙钛矿上赋予稳定性的假设。我们将通过旋涂和CVD来制作这些新材料的薄膜，并使用最新的XPS技术测试它们对水的稳定性。设想将建立用于稳定混合钙钛矿材料的新范例。

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.