Copper-doped cesium lead bromide colloidal nano-platelets

We have used ligand-assisted re-precipitation (LARP) technique to grow colloidal nano-platelets of Cu-doped cesium lead bromide (CsPbBr3) perovskite in room ambient. Using selected-area diffraction and transmission electron microscopy, the structure of the nano-crystals was identified to be the orthorhombic crystal phase. From green emission (520 nm) for the un-doped CsPbBr3 nano-crystals, we were able to shift the emission to blue (464 nm) for the 1% doped CsPbBr3 nano-platelets. As the doping concentration was increased, the edge length of nano-platelets increased and resulted in a decrease in the Stokes shift. Optical band gap was found to increase from 2.6 eV for the un-doped CsPbBr3 to 2.81 eV for the 2% doped sample. We report that the formation of excitons with binding energy in the regime 70–110 meV is responsible for the blue photoluminescence. The green emissions have been identified to be due to defect levels located at 210–380 meV below the conduction band edge. The PLE peaks exhibit no shift with increasing excitation wavelength signifying quantum confinement effect. The substitution of lead with copper provides an opportunity in making lead-free perovskite solar cells in the near future.