A roadmap towards stable perovskite solar cells: prospective on substitution of organic (A) & inorganic (B) cations

In recent years, the organic-inorganic hybrid perovskite solar cells (PSCs) have emerged as promising, fastest growing technology and achieved power conversion efficiency (PCE) as high as 25.5%. These hybrid PSCs exhibit many attractive properties such as long diffusion length, efficient charge transport, low temperature processing, tunable bandgap, and low-cost fabrication. The most conventional hybrid perovskite materials having the structure formula ABX(3), where A = MA/FA (organic cation), B = Pb2+ (inorganic cation), X = I/Cl/Br (halide anion) are very hygroscopic due to the presence of organic cation and toxic due to Pb content. For large scale use, the lead (Pb) toxicity could have deteriorating effects on the human race and the environment. Besides this, owing to the hygroscopic nature, the PSCs degrade very rapidly in humid conditions. Efforts have been reported to replace lead and organic cations from the perovskite compounds with suitable alternatives to manage the toxicity and stability. It has been found that the mixture of Pb and Sn could be more effective in terms of efficiency and toxicity. In other case, partial or complete replacement of organic moiety from the perovskite layer by inorganic cations such as cesium (Cs), rubidium (Rb) could lead to better thermal and moisture stability. The other materials such as Spiro OMeTAD, PEDOT: PSS, PTAA, used as hole transport layer (HTL) are quite expensive and degradable in ambient conditions. The suitable choice of inorganic HTLs in this regard would result in better stabilization of PSCs. All-inorganic PSCs is a way to improve the device performance.

Automated summary

Organic-inorganic hybrid perovskite solar cells have shown promising efficiency and properties, but the toxicity and hygroscopic nature due to lead and organic cations call for alternatives to improve stability.