Hot charge carriers in tin-based perovskite solar cells to exceed the Shockley-Queisser limit

太阳能电池中产生的电荷载流子由于热化而损失了相当一部分能量。这种损耗过程通常将太阳能电池的最大可实现功率转换效率限制在约33%。在这个项目中，我将研究一种材料系统——锡钙钛矿——其中载流子冷却得足够慢，从而能够成功地收集额外的能量。成功的实现将使理论上可实现的功率转换效率翻一番，达到66%。我的重点首先在于阐明锡钙钛矿中热载流子意外长寿命的起源。这些研究将主要通过单晶的时间分辨光致发光光谱进行，因为这种技术可以很好地评估载流子寿命，而且单晶往往比器件中使用的薄膜表现出更高的材料质量。组分的变化将使热载子寿命得到优化，并进一步加深对原子对寿命的影响的理解。在这些基础研究之后，载流子冷却将优化用于太阳能电池的薄膜。这尤其关系到晶界处电阱态的钝化。在项目的最后阶段，将对热载流子的提取进行演示。这就需要在材料上建立适当的电接触。为此，我建议使用低维纳米材料，我在博士工作期间研究过纳米材料的性质。与钙钛矿吸收层类似，所有必要的接触层都应该从溶液中沉积，以便于廉价和容易的处理。这是以后大规模生产太阳能电池的一个关键要求。

Generated charge carriers in solar cells lose a considerable portion of their energy as heat due to thermalisation. This loss process commonly limits the maximum achievable power conversion efficiency of solar cells to approximately 33%. In this project, I shall investigate a material system – tin perovskite – in which charge carriers cool down slowly enough to enable a successful harvesting of the additional energy. The successful implementation would double the theoretically achievable power conversion efficiency to 66%.My focus first lies on elucidating the origin of the unexpectedly long lifetime of hot-carriers in tin-perovskite. These investigations will chiefly be carried out through time resolved photoluminescence spectroscopy on single crystals, since this technique allows for a good assessment of the carrier lifetime and single crystals tend to exhibit a higher material quality than the thin films used in devices. Compositional variation will allow for the optimisation of the hot-carrier lifetime and furthermore give rise to a deeper understanding of the atomic impacts on the lifetime.Following these fundamental studies, the carrier cooling will be optimised for thin films usable in solar cells. This especially concerns the passivation of electrical trap states at grain boundaries.In the last phase of the project, the extraction of hot-carriers is to be demonstrated. This will require to establish a proper electrical contact to the material. To this end, I propose to use low-dimensional nanomaterials, whose properties I studied during my doctoral work.Analogous to the perovskite absorption layer, all necessary contacting layers ought to be deposited from solution, to allow for a cheap and easy processing. This is a crucial requirement for the later large-scale production of solar cells.