Growth and characterization of highly stable and layered 2D/3D perovskites for solar cells

Dissertation (MSc (Physics))--University of Pretoria, 2022.Perovskites of cesium lead halide (CsPbX3, X = Cl, Br, I) have received a lot of attention due to their relative stability in comparison to their organic-inorganic counterparts. This study synthesized a thin film of cesium lead tribromide (CsPbBr3) by spin coating followed by dip coating and characterized it through a scanning electron microscope (SEM), ultraviolet-visible (UV- Vis) spectrometer, and X-ray diffraction (XRD) in order to observe its morphological, optical and structural characteristics. SEM micrographs revealed pinholes within the perovskite film that significantly impacted device performance. To address this issue, we show that spin-coating phenethylammonium bromide (PEABr) on CsPbBr3 thin films improves morphology and surface coverage. The optical study of CsPbBr3 thin film showed a broad UV-Vis absorption with an onset at 530 nm and an excitonic peak at 515 nm. However, CsPbBr3/PEABr preserves the optical properties of CsPbBr3. Additionally, two excitonic peaks appear at 405 and 436 nm which are attributed to a 2D perovskite PEA2Csn-1PbnBr3n+1 with n = 1 and n = 2 phase. The viscosity of PEABr was also suggested to play a role in the decrease followed by an increase in absorption of CsPbBr3/PEABr films. XRD results of CsPbBr3 film showed the impurity phase of CsPb2Br5 and a cubic CsPbBr3 structure with the Pm-3m space group. Furthermore, PEABr had no effect on the intrinsic crystal structure of CsPbBr3. The CsPbBr3 solar cell produced a low open-circuit voltage (Voc) of 0.3 eV and a fill factor (FF) of 30.89%, which may due to the loss of charge-carriers in the area with pinholes. This could also explain the device's low power conversion efficiency (PCE) of 0.9%. A mixed-cation solar cell based on CsMAFAPb(IBr)3 was also designed and fabricated. This solar cell showed a photoluminescence emission at 766 nm with a charge carrier lifetime of 24 ns, which indicates that it is less prone to degradation. Current density-voltage (J-V) characteristics of CsMAFAPb(IBr)3 show a Voc and a FF of 1.14 eV and 57.32%, respectively. With this device, PCE of 13.89% was also achieved, with a short-circuit current of 23 mA/cm2. We conclude that these results may be related to the low hysteresis experienced at low voltage scan speeds of 10 mV/s. All things considered, the addition of an organic spacer to a 3D perovskite improves the morphological, optical, and structural characteristics of the as-prepared 3D perovskite film.National Research Fund (NRF).PhysicsMSc (Physics)Unrestricte