Insights from Semilab on Perovskite Solar Cells Investigation

These photovoltaic (PV) cells are constructed based on the distinctive structure of the perovskite crystal, often symbolized as ABX₃, with CaTiO₃ as a natural example.

Figure 1. Perovskite crystal example. Image Credit: Semilab Semiconductor Physics Laboratory

Organic-inorganic hybrid perovskites, derived from the ABX₃ arrangement, have emerged as promising materials for high-performance solar cells. In these hybrids,the A-site can include monovalent cations like methylammonium (CH₃NH₃₊), formamidinium (HC(NH₂)₂₊), or cesium (Cs+).

Meanwhile, the B-site can accommodate either lead (Pb₂₊) or antimony (Sb₂₊), and the X-site can be filled with halogen ions such as chlorine (Cl-), iodine (I-), or bromine (Br-).

Metrology

Spectroscopic ellipsometry (SE) is a useful method for analyzing different layers within the solar cell structure.

The Semilab SE-2000 can cover wavelengths from 190 nm to 25 μm. The thicknesses of layers and the optical dispersion of layer materials are determined by modeling the layer structure and adjusting the model parameters to align the simulated spectra with the measured ones.

Figure 2. SE-2000 metrology system. Image Credit: Semilab Semiconductor Physics Laboratory

Use Case

This investigation employed ellipsometry to analyze a series of samples prepared on glass substrates measuring 10×10 cm², including:

1. Single perovskite layer
2. Perovskite layer in a stack configuration.

A single perovskite layer on glass was an excellent reference sample for subsequent measurements of the perovskite layer in a stacked configuration.

Figure 3. Investigation of single perovskite layer. Image Credit: Semilab Semiconductor Physics Laboratory

The perovskite layer in a stacked configuration exhibited slight distinctions compared to the measurement of a single perovskite layer. These differences can be attributed to factors such as varying crystal sizes and defects within the stack.

Figure 4. Perovskite layer in a stack configuration. Image Credit: Semilab Semiconductor Physics Laboratory

By analyzing the extinction coefficient, the complete spectrum of the typical OPD* can be unveiled (Figure 5). The optical characteristics of perovskite materials can be harnessed to produce a band gap map (Figure 6).

Figure 5. *Optical penetration depth in perovskite layer. Image Credit: Semilab Semiconductor Physics Laboratory

Figure 6. Band gap map. Image Credit: Semilab Semiconductor Physics Laboratory 

UV Irradiation Effects

Perovskite materials are widely recognized for their sensitivity to ultraviolet (UV) light.

Figure 7. UV irradiation effects. Image Credit: Semilab Semiconductor Physics Laboratory

Long-Term Stability Investigation

After six months, several alterations were discernible in the optical spectra of the perovskite material.

Figure 8. Long term stability test. Image Credit: Semilab Semiconductor Physics Laboratory

Materials and Structures

Complex perovskite materials possessing the ABX₃ formulation, wherein A signifies an organic/inorganic cation, B represents a metal cation, and X symbolizes an anion.

References and Further Reading

Giles E. Eperon et al. Formamidinium lead trihalide: a broadly tunable perovskite for efficient planar heterojunction solar cells. Energy & Environmental Science, Volume 7, Issue 3, March 2014, Pages 982-988, doi: 10.1039/c3ee43822h.

This information has been sourced, reviewed and adapted from materials provided by Semilab Semiconductor Physics Laboratory.

For more information on this source, please visit Semilab Semiconductor Physics Laboratory.