SOLAR: Enhanced Photovoltaic Efficiency through Heterojunction Assisted Impact Ionization

该项目结合了来自三所大学的薄膜合成、分析和建模专业知识，探索在无偏半导体异质结构和纳米结构薄膜中实现大于1的量子效率的可能性。这种方法被称为异质结辅助冲击电离，它将窄带隙主体材料与薄膜、纳米棒或纳米颗粒形式的宽带隙吸收剂结合在一起。在宽隙材料中由高能量光子产生的载流子漂移到窄隙材料中，在窄隙材料中通过撞击电离衰变产生额外的载流子。该项目探索了具有适当波段对准和生长特性的半导体材料的有前途的组合，以促进冲击电离，同时最大限度地减少其他重组途径。这项努力的成功将导致使用环保材料提高太阳能电池的效率。21世纪最大的科学挑战之一是开发一种技术，能够以合理的成本大规模地将太阳光转化为电能。大多数太阳能电池的效率受限于光吸收的单位量子效率，即每个光子最多产生一个电子电荷。这对于波长较短的光来说尤其成问题，因为波长较短的光对应于能量较高的光子，因为被吸收的光子能量的很大一部分被转化为废热。该项目旨在设计和优化纳米结构半导体材料，优先将这些多余的能量转化为额外的电荷产生，而不是废热。这种方法可以很容易地适用于现有光伏设备中使用的材料，并且还提出了一种全新的环保材料，用于太阳能转换。通过对学生的培训，该项目将有助于培养下一代科学家和工程师，为解决与社会相关的问题做好充分准备。

This project combines thin film synthesis, analysis, and modeling expertise from three universities to explore the possibility of achieving quantum efficiency greater than one in unbiased semiconducting heterostructures and nanostructured thin films. The approach, called heterojunction-assisted impact ionization, combines a narrow band gap host material with wide band gap absorbers in the form of thin films, nanorods, or nanoparticles. Carriers generated by higher energy photons in the wide-gap material drift into the narrow-gap material where they decay through impact ionization to produce additional carriers. The project explores promising combinations of semiconducting materials with appropriate band alignment and growth characteristics to promote impact ionization while minimizing other recombination pathways. Success in this endeavor will lead to improved solar cell efficiency using environmentally benign materials.One of the grand scientific challenges of the 21st century is the development of a technology that can convert sunlight to electricity on a large scale at reasonable cost. The efficiency of most solar cells is limited by unit quantum efficiency of light absorption, that is, each photon of light produces at most one electron of charge. This is particularly problematic for shorter wavelength light, which corresponds to higher energy photons, since a large fraction of an absorbed photon's energy is converted into waste heat. This project aims to design and optimize nanostructured semiconducting materials that preferentially channel this excess energy into additional charge generation rather than waste heat. The approach can be readily adapted to materials used in existing photovoltaic devices and also suggests entirely new classes of environmentally benign materials for application in solar energy conversion. Through the training of students, the project will help foster the next generation of scientists and engineers, well-prepared to address problems relevant to society.