Abstract:
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.
