创新背景

电荷以带负电荷的自由电子和带正电荷的“空穴”的形式存在。电子是在材料中移动的亚原子粒子，而空穴是指在原子晶格中没有电子，而电子可能存在的地方。空穴吸引自由电子，可以被认为是带正电的准粒子。当两者结合时，或者更确切地说，当一个电子填满一个空穴时，它们会有效地消失，不再移动，这意味着它们不再传输电荷。

自然光合作用的基本过程之一是电子从空穴中分离出来，然后“收集”这些自由的、带电的准粒子——称为“载流子”。

创新过程

并非所有的载体都是一样的。当受到广谱光源（如太阳）的激发时，载流子变得非常兴奋并携带大量能量——成为“热载流子”。不久之后，它们就会降至较低的能量状态，成为“放松的携带者”。目前，太阳能电池板只能分离和收集松散的载流子，这也是太阳能电池板效率徘徊在15%-20%范围的部分原因。

如果能捕获传输更多能量的热载体，研究人员就能从太阳能中获取三到四倍的能量。这项新研究首次证明了电荷分离过程导致热载流子的聚集。他们在金属（金）和半导体（氮化镓）之间制造了一个结，然后用激光脉冲激发电子——空穴对。在每个激光脉冲后不到200飞秒，在载流子还没有时间放松到一个较低的能量状态之前，他们用另一束叫做探针的光撞击这对电子，将电子从空穴中分离出来，并保持空穴打开，在它们仍然“热”的时候“收集”它们。（作为参考，飞秒是十亿分之一秒的百万分之一。）

除了收集热孔，该团队还能够观察到孔是如何放松到较低的能量状态的，从而深入了解这个过程是如何工作的。他们发现，当捕获一个热空穴时，它改变了成对热电子的弛豫动力学。研究人员的目标是同时收集电子和空穴，但他们却能够收集空穴并观察弛豫过程。他们并没有预料到电子和空穴弛豫过程会如此相互依赖。

创新关键点

这项新研究首次证明了电荷分离过程导致热载流子的聚集。他们在金属（金）和半导体（氮化镓）之间制造了一个结，然后用激光脉冲激发电子——空穴对。

创新价值

这项基础研究有一天可以帮助科学家从太阳获取能量，比植物利用自然光合作用更有效。

Innovative use of solar energy to capture thermal "charge carriers" into usable energy

Not all carriers are the same. When excited by a broad-spectrum light source, such as the sun, carriers become very excited and carry a lot of energy - "hot carriers". Soon after, they drop to a lower energy state and become "carriers of relaxation." Currently, solar panels can only separate and collect loose charge carriers, which is partly why solar panel efficiency hovers in the 15-20% range.

By trapping heat carriers that transmit more energy, researchers could extract three to four times as much energy from solar energy. This new study is the first to demonstrate that the charge separation process leads to the aggregation of hot charge carriers. They created a knot between a metal (gold) and a semiconductor (gallium nitride), then excited the electron-hole pair with a laser pulse. Less than 200 femtoseconds after each laser pulse, before the carriers have had time to relax into a lower energy state, they hit the pair with another beam of light called a probe, separating the electrons from the hole and keeping the hole open to "collect" them while they are still "hot." (For reference, a femtosecond is a millionth of a billionth of a second.)

In addition to collecting the hot holes, the team was also able to observe how the holes relax to lower energy states, giving insight into how the process works. They found that when trapping a hot hole, it alters the relaxation dynamics of pairs of hot electrons. The researchers' goal was to collect both electrons and holes, but they were able to collect holes and observe the relaxation process. They did not expect the electron and hole relaxation processes to be so interdependent.