Rare earth doped perovskites for efficient solar spectrum down-conversion

Perovskites doped with rare earth (RE) ions can be used to convert efficiently UV component of solar radiation spectrum in the near-infrared (NIR) radiation suitable for generating electricity in conventional silicon-based photovoltaic (PV) cells. These materials have good ability to capture the energy of the incident UV photons and transfer it to the embedded RE ions, such as Yb³⁺ emitting NIR photons. In this paper we explored two methods of synthesis of down-converting REdoped metal halide perovskites CsPbCl_xBr_1-x: Yb³⁺: the hot injection method of making nanoparticles (NP) and the two-stage spin-casting fabrication of the nano-films. The hot-injection method resulted in the NP with an average size varying from 4 to 120 nm. The XRD spectroscopy revealed that the synthesized NP had the crystalline structure like orthorhombic bulk crystal of CsPbBr3. The PL spectrum of the Yb³⁺ perovskite NP revealed the NIR PL peak at 980 nm attributed to the relaxation of the excited ion of Yb³⁺ and indicating that the process of spectral down-converting (quantum cutting) took place. Besides well-known dependence of the color of visible PL on the composition of the perovskite CsPbX3 (blue for X = Br, yellow – X = Cl, and red – X = I), we showed that the wavelength of the visible PL peak increases with the average size of the NP of CsPbCl_1.5Br_1.5. The nano-films of CsPbCl_xBr_1-x: Yb³⁺ prepared by the spin-casting method demonstrated visible PL of blue-green color. The obtained results might be of significance to the applications related to the efficient solar power and green power technology.