Unravelling ultrafast charge recombination and transport dynamics in hybrid perovskites.

对于多晶半导体来说，杂化钙钛矿的光致发光(PL)效率非常高。我是第一个报道这一点的人，就像垂直腔体结构中的激光一样，我还进一步证明了强大的辐射发射是钙钛矿在太阳能电池(报道的功率转换效率&gt；20%)和发光二极管(我们实验室的外部量子效率现在&gt；18%)中表现优异的关键。未来的收益将需要了解和控制整体和电极上的非辐射损失。我们的初步结果表明，光致发光是由自由电荷的重新组合产生的，但现在需要新的物理概念来理解这个过程如何在保持低非辐射损失的同时，提供如此出人意料的高辐射产额。与典型的高发射III-V量子井系统相比，报告的长寿命带来了更长的尺度。材料的不均匀性是一个核心参数，因为电子和空穴在复合之前对大量样品进行了采样，这可能会改变它们的物理性质和相互作用。最先进的PL研究记录了时间分辨率约为100 ps的空间平均信息，这是因为在短时间尺度上记录本地信号存在挑战。然而，我们已经发现载流子相互作用已经在亚皮秒时间内，这可能会在更长的时间尺度上影响复合。在这些快速的时间尺度上探索PL，现在将给我们提供一个新的物理制度的洞察力。为此，我们的新技术将把超快光谱分辨发光与空间显微镜结合起来，这将把时间和空间分辨率的最先进水平提高一个数量级，达到亚皮秒和亚微米的范围。我们将使用这种新的装置来研究由本征性质(由载流子-载流子相互作用控制)主导的区域中的载流子复合和扩散，这将使我们能够解开外在效应(由材料属性，如陷阱控制)。同时，局部探测将解决材料形态对复合和局部化的影响。我们的研究将对杂化钙钛矿的光物理提供前所未有的洞察，在以前无法到达但高度相关的时间和空间区域。我们的发现将为实现混合钙钛矿中异常高效的辐射复合的物理和材料来源建立一幅新的图景，这将是解锁设备性能收益的关键。

The photoluminescence (PL) efficiency of the hybrid perovskites are exceptionally high for a poly-crystalline semiconductor. I was the first to report this, as exemplified by lasing in vertical cavity structure, and I have gone on to demonstrate that the strong radiative emission is key for the perovskites' exceptional performance in solar cells (power conversion efficiency >20% reported) and light-emitting diodes (external quantum efficiency now >18% in our labs). Future gains will require understanding and control of the non-radiative losses both in the bulk and at the electrodes. Our initial results showed that the PL arises from the recombination of free charges, but new physical concepts are now required to understand how this process can give such unexpectedly high radiative yields, while maintaining low non-radiative losses. The reported long lifetimes bring much longer length scales into play, compared to typical high-emission III-V quantum-well systems. Material inhomogeneity is a central parameter, since electrons and holes sample large volumes before recombination, which potentially changes their physical properties and interactions. State-of-the art PL studies recorded spatially-averaged information with time-resolution around 100 ps, due to challenges in recording local signals on short timescales. Yet, we have found carrier interactions already on sub-picosecond times, which are likely to affect recombination at longer time scales. Probing PL at these fast timescales, will now give insights into a new physical regime. For this, our new technique will combine ultrafast spectrally-resolved PL with spatial microscopy, which will advance the state-of-the art in temporal and spatial resolution by an order of magnitude to sub-picosecond and sub-micrometre regimes. We will use this new setup to study carrier recombination and diffusion in a regime dominated by intrinsic properties (controlled by the carrier-carrier interactions), which will allow us to untangle extrinsic effects (controlled by material properties such as trapping). Simultaneously, local probing will resolve the impact of material morphology on recombination and localisation. Our study will give unprecedented insights into the photo-physics of hybrid perovskites in previously inaccessible, yet highly relevant, temporal and spatial regimes. Our findings will establish a new picture on the physical and material origin enabling the exceptionally-efficient radiative recombination in hybrid perovskites, which will be crucial for unlocking gains in device performance.