Innovations and Applications of Perovskite Solar Cells

As global energy consumption continues to grow and environmental pollution becomes increasingly severe, replacing traditional energy sources with clean, renewable energy sources is imminent. Solar energy is widely used because it is widely distributed. Perovskite Solar Cells are the most important way to use solar energy, and a new type of solar cell with perovskites as its light-absorbing material has developed rapidly. The conversion efficiency of organic solar cells with perovskite structure can be as high as 22.1%, and the cost of solar cells can be significantly reduced. Perovskite crystals exhibit excellent performance and strong competitiveness in the field of solar cells. They have the advantages of low cost of organic materials, solution preparation, and easy film formation. They also have the advantages of high mobility of inorganic materials and high absorption coefficient. The titanium ore crystal itself can absorb light, generate carriers and transmit carriers, and the battery performance quickly exceeds DSSC and BSC (third generation solar cells).

Figure 1. Perovskite solar cells

Work mechanism of perovskite solar cells

Perovskite refers to an organic-inorganic hybrid material with a crystal structure of a perovskite crystal whose molecular formula is ABX₃ (A = organic cation, B = Pb, Cd, or Sn, X = I, Cl, or Br). For example, the CH₃NH₃PbI₃ cell consists of one Pb²⁺ ion, one CH₃NH₃⁺ ion, and three I^- ions. The metal cation and halogen anion form a positive octahedral structure, and the organic cation balances the charge. Under light irradiation, the electrons of I can be excited on Pb , and electron migration occurs.

Figure 2. Crystal structure of ABX₃

Perovskite solar cells originate from the third generation solar cell DSSC. The initial structure Meso-super-structured solar cells (MSSCs) is the evolution of DSSC. The simple structure is described as follows: Firstly, a dense TiO₂ layer is prepared as an electron transport layer (ETL) on a fluorine-doped tin oxide/indium-doped tin oxide (FTO/ITO) conductive glass, and a TiO₂ (or Al₂O₃) mesoporous is prepared as well. Material (or nanoparticle layer), then the perovskite light absorbing layer is prepared, if necessary, a hole transport layer (HTL) may be spin-coated on the light absorbing layer, and finally the metal electrode is evaporated to obtain a battery.

Figure 3. Structure for typical MSSCs

The earliest perovskite solar cells used a perovskite layer as a light-absorbing layer and a transport layer to prepare MSSC, and later a perovskite cell containing a porous metal oxide structure was developed. Due to the preparation of TiO₂/Al₂O₃ mesoporous materials after high-temperature sintering, many research groups began to develop and process normal-temperature Planar Heterojunction (PHJ) perovskite solar cells. For example, professor Chen design the structure of ITO/PEDOT (PEDOT = polyethylene Dioxythiophene) / CH₃NH₃PbI₃/C₆₀/BCP (BCP = Bath Copper) / Al battery.

Figure 4. Planar heterojunction perovskite solar cells

The main factors affecting the performance of perovskite solar cells

The performance of perovskite solar cells is significantly influenced by several key factors, primarily related to the structure and composition of the perovskite material itself. At the molecular level, perovskite crystals, with the generic formula ABX3, comprise an organic cation (A+), a metal cation (B2+), and a halogen anion. This composition forms a complex crystal structure where the arrangement and type of each of these components can drastically affect the material’s properties.

Adjustments to the chemical composition of these components can alter the energy levels, charge mobility, absorption spectrum, and overall performance of the solar cells. For instance, varying the organic cations or substituting different metal ions can lead to changes in the electronic properties of the material. These changes can optimize the cell for specific applications or improve its operational efficiency.

Moreover, the crystallinity and morphology of the perovskite layer, particularly the light-absorbing layer, are crucial in determining the solar cell’s efficiency. High crystallinity ensures that the material has fewer defects, which improves charge mobility and reduces recombination losses. Achieving a uniform morphology with complete coverage minimizes the presence of defects such as pinholes, which can cause short circuits and reduce the overall performance of the device.

To address these challenges, scientists and researchers have developed a plethora of innovative methods and techniques. These methods focus on improving the uniformity and crystallinity of the perovskite films, ensuring they are dense and well-formed. Techniques such as solution processing, vapor deposition, and additive engineering are employed to fine-tune the film formation process, producing layers that have optimal thickness, minimal roughness, and superior optical and electronic properties.

The aim of these techniques is to enhance the fill factor, which refers to the solar cell’s ability to convert sunlight into electricity efficiently. A higher fill factor directly correlates with increased photocurrent (the current produced by the cell under illumination) and overall cell efficiency, leading to more effective and commercially viable solar technology.

Furthermore, the elimination of defects in the perovskite layer aids in maintaining a stable and reliable performance over time, which is critical for the commercial adoption of perovskite solar cells. Ultimately, ongoing research and innovation in this field are driving the development of perovskite solar cells towards becoming a mainstream, sustainable energy solution, offering a promising alternative to traditional silicon-based solar technology.

References

1. Mitzi D B, Feild C A, Harrison W T A. Conducting tin halides with a layered organic-based perovskite structure[J]. Nature, 1994, 369(6480): 467.
2. Wang Y, Gould T, Dobson J F. Density functional theory analysis of structural and electronic properties of orthorhombic perovskite CH₃NH₃PbI₃[J]. Physical Chemistry Chemical Physics, 2013, 16(4): 1424-1429.
3. Gao P, Grätzel M, Nazeeruddin M K. Organohalide lead perovskites for photovoltaic applications[J]. Energy & Environmental Science, 2014, 7(8): 2448-2463.