Bandgap tuning with thermal residual stresses induced in a quantum dot

Lattice distortion induced by residual stresses can alter electronic and mechanical properties of materials signifi cantly. Herein. A novel way of the bandgap tuning in a quantum dot (QD) by lattice distortion is presented using 4-nm-sized CdS QDs grown on a TiO ₂ particle as an application example. The bandgap tuning (from 2.74 eV to 2.49 eV) of a CdS QD is achieved by suitably adjusting the degree of lattice distortion in a QD via the tensile residual stresses which arise from the difference in thermal expansion coeffi cients between CdS and TiO ₂. The idea of bandgap tuning is then applied to QD-sensitized solar cells, achieving ∼60% increase in the power conversion effi ciency by controlling the degree of thermal residual stress. Since the present methodology is not limited to a specifi c QD system, it will potentially pave a way to unexplored quantum effects in various QD-based applications.