Perovskite solar cells recycle photons
Inorganic-organic perovskite solar cells are very efficient in part because the charge carriers exhibit very long path lengths. Pazos-Outón et al. show that photon recycling, as seen previously in highly efficient gallium arsenide solar cells, contributes to this effect (see the Perspective by Yabionovitch). In most solar cells, the recombination of photogenerated charge carriers (electrons and holes) wastes all of the energy. In these lead tri-iodide cells, recombination emits a photon that can be reabsorbed and create more charge carriers.
Abstract
Lead-halide perovskites have emerged as high-performance photovoltaic materials. We mapped the propagation of photogenerated luminescence and charges from a local photoexcitation spot in thin films of lead tri-iodide perovskites. We observed light emission at distances of ≥50 micrometers and found that the peak of the internal photon spectrum red-shifts from 765 to ≥800 nanometers. We used a lateral-contact solar cell with selective electron- and hole-collecting contacts and observed that charge extraction for photoexcitation >50 micrometers away from the contacts arose from repeated recycling between photons and electron-hole pairs. Thus, energy transport is not limited by diffusive charge transport but can occur over long distances through multiple absorption-diffusion-emission events. This process creates high excitation densities within the perovskite layer and allows high open-circuit voltages.
Science 25 Mar 2016:
Vol. 351, Issue 6280, pp. 1430-1433
DOI: 10.1126/science.aaf1168
http://science.sciencemag.org/content/351/6280/1430
无机-有机钙钛矿太阳能电池具有很高的能量转化效率，部分原因是由于载流子有很长的传输距离。Pazos-Outon等人发现，钙钛矿电池中的光循环效应可以解释这一现象。在大部分电池中，光生载流子（电子和空穴）的复合会损失全部的能量。而在碘化铅钙钛矿太阳能电池中，载流子的复合可以产生光子，光子再被吸收，从而再次生成载流子。（Science DOI:10.1126/science.aaf1168）（新材料在线）
钙钛矿结构的铅-卤化物具有高性能光伏材料的特征。我们将光致发光的传播与来自于钙钛矿结构三碘化铅薄膜局部光激励点的电荷进行映射，并在大于等于50微米的距离范围内观察到光子的发射，并且发现内部光子光谱的峰值发生了从765纳米到800纳米以上的红移。本文使用选择性电子-空穴聚集接触的侧向接触式太阳能电池，观察到离接触点50纳米以上的光致发光的电荷提取是由于光子和电子-空穴对之间的反复循环所致。因此，能量传输并不局限于扩散的电荷输送，且存在于持续长距离的多重吸收-扩散-发射作用中。这一过程能够创建钙钛矿结构层次中的高激发密度，并容纳较高的开路电压。（科研圈）
