Targeted compositional engineering towards thermally stable efficient solution-processed perovskite solar cells

Abstract

Perovskite Solar Cells (PSC) being the future of all photovoltaic technology, has gained much interest in its research. The popularity of the PSC are based on the direct band gap electronic structure with high absorption coefficient, outstanding photo-physical properties and tuneable electronic structure by varying species of the AB𝑋3 structure, with low cost versatile fabrication methods. These advantages further spur the interest of research after reaching performance that is comparable to the mature Silicon Photovoltaic (PV) technologies. Unfortunately, the biggest challenge restricting the Perovskite PV technologies are issues in their stabilities, (e.g. moisture, oxygen and heat). Therefore, increasing efforts has been channelled in the hope to improve the stability of the PSC. This project focuses on approaches to help improve the stability of slot die-coated perovskite solar cells towards both moisture and heat. Three thermal stability improvement technique such as the substitution of the A- site Cation in the perovskite, substitution X-site anions in the perovskite and changing the dimensionality of the perovskite are employed in this experiment. First, the A-site cation of two different compositions, FA0.85Cs0.15Pb(I0.83Br0.17)3 and MAPbI3 are tested in this experiment. From the results we can see that by changing the A-site cation from MA to FACs, thermal stability can be improved as FACs will be able to form 3D perovskite at room temperature which is essential for its performance. Next, by varying the X-site anion of the perovskite can also affect the stability of the perovskite. FA0.85Cs0.15PbI3 and FA0.85Cs0.15Pb(I0.83Br0.17)3 perovskite were tested and compared. Mixed halide perovskite was able to achieve better phase stability at room temperature than pure iodide perovskite. However, it is observed that full iodide perovskite is thermally more stable than mixed halide perovskite. This is due to the smaller bandgap of the iodide perovskite. Lastly, thermal stability of the PSCs can be improved by changing the dimensionality of the perovskite. FPEA is an organic molecule which has the ability to split the three-dimensional (3D) perovskite into lower dimensions. Low dimension perovskites are able to achieve higher stability towards moisture and heat. Therefore, by mixing FPEA with the 3D perovskite, it can achieve improved stability and performance. Improve in moisture stability is due to the hydrophobicity of the FPEA. Our work presents a major proof of demonstration that perovskite solar cells can be stabilized against external stressors such as moisture and heat.