Investigation of phonon scattering in superlattices for design of efficient multiple quantum-well hot carrier solar cells

热载流子太阳能电池是一种太阳能转换器，其捕获半导体中光生电子和空穴的多余热能以产生电力。热载流子太阳能电池有望产生超过传统限制的显著更高的效率。用于实现高效率热载流子太阳能电池的有前景的材料系统涉及多个量子威尔斯，其由布置在称为超晶格的交替层中的半导体材料组成，以有效地减少来自热电子的能量损失。来自电子的能量损失通过能量耗散到高能晶格振动而发生，高能晶格振动通过散射进一步耗散到低能晶格振动。通过最小化散射将高能量与低能量晶格振动解耦可以最终提高太阳能电池效率。在拟议的研究中，项目团队将应对这一挑战，并通过设计超晶格成分和应变半导体晶体来设计高效的热载流子太阳能电池。半导体中的主要声子散射机制是Klemens通道，其涉及光学声子衰减为两个声学声子。通过改变超晶格组成，可以改变声子色散中的能隙，从而提供抑制声子散射中的Klemens样通道的途径。这可以实现更长的声子寿命，导致非平衡声子种群，从而促进电子热化中的热声子瓶颈。应变可以类似地修改声子色散，再次允许减少声子散射的可能性。超晶格成分和应变的作用将在两个超晶格系统- InAs/AlSb和AlAs/GaAs中进行研究。分析将通过第一原理的方法，使用谐波和非谐波力的相互作用，从密度泛函理论沿着与声子玻尔兹曼输运方程的解决方案进行。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

The hot carrier solar cell is a type of solar energy converter that captures the excess thermal energy of photo-generated electrons and holes in a semiconductor to produce electric power. Hot carrier solar cells hold the promise of yielding significantly higher efficiency beyond traditional limits. A promising material system for achieving high efficiency hot carrier solar cells involves multiple quantum wells, comprised of semiconductor materials arranged in alternating layers known as superlattices, to effectively diminish energy loss from hot electrons. Energy loss from electrons occurs by dissipation of energy to high energy lattice vibrations, which further dissipate to low energy lattice vibrations by scattering. Decoupling the high energy from low energy lattice vibrations by minimizing scattering can ultimately enhance the solar cell efficiency. In the proposed research, the project team will tackle this challenge and design high-efficiency hot carrier solar cells through engineering the superlattice composition and by straining the semiconductor crystal. A dominant phonon scattering mechanism in semiconductors is the Klemens channel, which involves decay of an optical phonon into two acoustic phonons. By modifying superlattice composition, the energy gap in the phonon dispersion can be modified providing avenues to suppress Klemens like channels in phonon scattering. This can enable longer phonon lifetimes, resulting in non-equilibrium phonon populations, thus facilitating hot phonon bottleneck in the thermalization of electrons. Strain can similarly modify phonon dispersion, again allowing for the possibility to diminish phonon scattering. The role of superlattice composition and strain will be studied in two superlattice systems - InAs/AlSb and AlAs/GaAs. Analysis will be performed through a first-principles approach by using harmonic and anharmonic force interactions derived from density-functional theory along with a solution of the phonon Boltzmann transport equation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.