Based on interface optimization and component regulation, the power conversion efficiencies (PCEs) of perovskite solar cells have increased rapidly. However, poor environmental stability still a major factor hinders the commercialization of perovskite solar cells.

Recently, 3D-2D perovskite stacking structures have been attracting extensive interest, which not only integrated the advantages of enhanced stability in 2D perovskites but also combined the strong light absorption and good charge carrier transport properties in 3D perovskite materials.

In a study published in Advanced Energy Materials, a research group led by Prof. GAO Peng from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported 2-(4-fluorophenyl)ethylamine (FPEA: 4-FC₆H₄C₂H₄NH₃) bulky cation to grow a 2D perovskite overlayer on the top of the Cs/FA/MA triple-cation 3D perovskite to combine the high stability of 2D perovskite with high efficiency of 3D perovskite simultaneously.

The density functional theory (DFT) calculations based on the defect model evaluated the slab surface energies of three kinds of perovskite crystals, the triple-cation mixed 3D perovskite, PEA₂PbI_4, and FPEA₂PbI₄, respectively. The defect formation energy of (FPEA)₂PbI₄ is much higher than that of (PEA)₂PbI₄, which will benefit more to enhance the stability when it is deposited on top of a 3D perovskite.

By performing X-ray diffraction (XRD), photoluminescence (PL), and Laser Scanning Confocal Microscope (LSCM) experiments, the researchers confirmed the formation and distribution of (FPEA)₂PbI₄ crystals on top of the 3D perovskite.

Employing the 3D-2D perovskite as the absorbing layer in the photovoltaic cells, they realized a high power conversion efficiency of 20.54% with a higher V_OC of 1.126 V, a J_SC of 22.80 mA cm^-2, and an FF of 0.80.

In addition, the researchers achieved a stabilized efficiency of 20.26% by introducing 2 mg mL^-1 FPEAI/IPA solution onto the 3D perovskite films with greatly enhanced stability than the control cell sustaining 99% of their initial efficiency after 864 h.

Further study is underway in the lab exploring more hydrophobic aromatic fluorocarbons to improve the micromorphology of the perovskite layer and moisture- resistant properties of PSCs.

Device architecture of the PSCs and corresponding cross-sectional Scanning Electronic Microscope (scale bar: 200 nm). (Image by Prof. GAO’s group)