Improved Stability of Organometal Halide Perovskite Films and Solar Cells toward Humidity via Surface Passivation with Oleic Acid

Abstract

Organometal halide (OMH) perovskites are highly promising for photovoltaic (PV) and other applications. However, their instability toward environmental factors such as humidity presents a major challenge in their potential commercial use. In this study, we developed a method to modify the surface of CH 3 NH 3 PbI 3 perovskite films by spin coating oleic acid (OA) to create a water resistant layer that results in enhanced stability and PV performance. The OA-surface passivated perovskites were studied using FT-IR spectroscopy, UV−vis absorption spectroscopy, and X-ray diffraction (XRD). The samples were aged in dark humid air at ∼76% relative humidity (RH) for 4 weeks. The surface passivated films showed minimal signs of decomposition, and the PV devices showed better performance than the unpassivated devices. A possible explanation is the carboxyl group (−COO − ) of OA binds to surface Pb 2+ and/or CH 3 NH 3 + to both passivate these surface defect sites, resulting in the formation of a thin layer of OA with their hydrophobic tail away from the perovskite film surface that effectively prevents water molecules from reaching the perovskite.

Understanding Hydrogen Bonding Interactions in Crosslinked Methylammonium Lead Iodide Crystals: Towards Reducing Moisture and Light Degradation Pathways

“…[4][5][6][7][8] These approaches include modification of the perovskite structure via halide engineering, [9][10][11][12] cation substitution and the addition of dopants, [13][14][15][16][17] interface engineering, [18][19][20][21][22] and surface passivation [23] or encapsulation via small molecules or waterproof layers. [4][5][6][7][8] These approaches include modification of the perovskite structure via halide engineering, [9][10][11][12] cation substitution and the addition of dopants, [13][14][15][16][17] interface engineering, [18][19][20][21][22] and surface passivation [23] or encapsulation via small molecules or waterproof layers.…”

“…Several approaches have been developed to unravel the limited stability of organic-inorganic perovskite crystals regarding oxygen, moisture,and UV light exposure. [4][5][6][7][8] These approaches include modification of the perovskite structure via halide engineering, [9][10][11][12] cation substitution and the addition of dopants, [13][14][15][16][17] interface engineering, [18][19][20][21][22] and surface passivation [23] or encapsulation via small molecules or waterproof layers. [24,25] Studies on mixed-halide perovskites,w ith the structure CH 3 NH 3 PbI 3Àx Cl x or CH 3 NH 3 PbI 3Àx Br x ,h ave been reported to show increased efficiencies and stability in air in contrast to their tri-iodide counterparts.…”

Surface Passivation of Perovskite Films via Iodide Salt Coatings for Enhanced Stability of Organic Lead Halide Perovskite Solar Cells

“…This in turn has led to the development of various strategies to improve film and device stability. These strategies include modification of the crystal with caesium ions or alternative organic groups such as formamidinium; partially replacing iodide with bromide to obtain mixed‐halide perovskites; encapsulating devices with hydrophobic polymer layers; implementing chromium oxide‐chromium (Cr 2 O 3 /Cr) interlayers to prevent metal contacts from reacting with the perovskite layer; fabricating solar cells with all‐solution‐processed metal oxide charge transport layers, surface passivation of MAPbI 3 layers with oleic acid . A very recent study also have shown that Zn 0.8 Cd 0.2 S nanoparticles (ZCS) doped in PCBM could improve electron transport within electron transporting layer (ETL) and effectively suppress interfacial charge recombination, enhancing material, and device stability …”

Barrier Designs in Perovskite Solar Cells for Long‐Term Stability

“…Organic materials with long alkyl chains or other hydrophobic groups could restrict the ingress of moisture. [129][130][131][132] The shielding effect can be further enhanced when conjugated and cross-linked polymers with network structures are used, which can prevent the outward ion diffusion from perovksite. [133][134][135][136] One important advantage of organic materials is their flexibility, which is benefit for the formation of compact wrapping layer around perovskites.…”