异质结电荷转移的密度矩阵理论近似研究*

摘要

Heterogeneous structure of a molecule semiconductor is the essential part of dye-sensitized solar cell, and the charge injection in it is the key factor of efficiency of solar energy conversion. A heterogeneous system is investigated where a metal nano-particle is used to decorate the structure of dye molecules and TiO2 semiconductor. Photoinduced charge injection dynamics from the molecule dye to TiO2 lattice is studied using density matrix theory. Simulations can account for the semiconductor lattice structure, the reflection of electron wave function in the lattice boundary, as well as the plasmon effect of the metal nano-particles. The compound treatment of density matrix theory and wave function approach is verified to be an efficient way for calculating the plasmon effect in the heterogeneous system. It is found that the plasmon enhancement due to the photoexcitation of metal nano-particles can reach as high as 3 orders of magnitude, which is shown to be an efficient way of improvement of charge conversion. The approach of density matrix theory and wave function treatment makes it possible to simulate the charge transfer in large-scale bulk semiconductor, the result of which is helpful for the theoretical analysis of plasmon enhancement in charge transfer dynamics.%分子半导体组成的异质结构是染料敏化太阳能电池的主要部分，电荷转移效率的提高是太阳能转换效率的关键。在金属纳米粒子与染料分子和半导体TiO2组成的系统中，考虑半导体的晶格结构、电子波函数在晶格边界的反射及金属纳米粒子中的等离激元效应，应用密度矩阵理论研究在光激发分子作用下电荷从分子转移到半导体晶格的动力学过程，采用密度矩阵和波函数相结合的处理方案研究了分子半导体电荷转移过程中的等离激元效应。研究发现金属钠米粒子激发所产生的等离激元可以使电荷从分子到半导体的转移效率提高3个数量级，是提高电荷转移效率的有效手段，且密度矩阵理论与波函数相结合的方法使得计算分子与15 nm尺度的半导体纳米晶体间的电荷转移成为可能，理论分析了表面等离激元的增益作用对电荷转移的影响。