Size-dependent nonlinear optical absorption in SnO₂ quantum dots

Abstract

Using a Z-scan technique, we report size-dependent changeover from reverse saturable absorption to saturable nonlinear optical absorption properties of as-deposited and annealed stannic oxide semiconductor quantum dot thin films, prepared by a sol-gel technique on a quartz substrate. The average size of quantum dots, as obtained from grazing incident x-ray diffraction, was found to be in the range of the exciton Bohr radius. Atomic force microscopy data confirmed the spherical shape of quantum dots. The UV-Vis data of the films displayed bandgap enhancement due to the combined effect of Coulombic and confinement potentials. A density matrix analysis was conducted to obtain the transition energy-dependent nonlinear optical absorption coefficient in the cw excitation regime. We found a qualitative agreement between the experimental observations and theoretical calculations.

Solution-Processed SnO2 Quantum Dots for the Electron Transport Layer of Flexible and Printed Perovskite Solar Cells

“…Using SnO 2 QDs instead of NPs provides the advantage of having a thin, dense, and uniform film of ETL. QDs have a wider bandgap (about 4.20 eV) compared to NPs, and this enhances the optical transmittance of the resulting ETL [ 43 ]. The main issue that limits the use of SnO 2 ETL for flexible devices is its annealing temperature, which has been found > 150 °C, while the typical flexible substrates such as PET and PEN usually have temperature limitations in terms of their structural integrity [ 40 , 44 , 45 , 46 ].…”