BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to electronic devices, such as, without limitation, solar cells and light emitting diodes, and more particularly to a highly stable electronic device, such as a perovskite solar cell, that includes a hydrophobic composite coating layer for protecting the electronic device from environmental conditions such as humid air and radiant heat.

2. Description of the Related Art

Solar energy has attracted huge attention as a promising alternative to fossil fuel energy (which is regarded as a major source of the green-house effect). However, to replace fossil fuel energy on a worthwhile scale, the manufacturing costs of solar cells need to be decreased and/or the power conversion efficiency of solar cells need to be increased. Recently, organic-inorganic perovskite semiconductors, such as halide perovskite (CH3NH3PbX3, X=halogen ions), have been found to be an excellent light absorber for use in creating highly efficient and economically viable solar cells, known as halide perovskite solar cells (PSCs). Halide perovskites have outstanding optical and electronic properties, such as a high absorption coefficient (>104cm−1), a long carrier diffusion length (>1 μm), high carrier mobility (25 cm2/Vs), and a suitable band gap spanning the energy of visible and near infrared light. In addition, simple and cheap synthesis processes can be applied to the large scale production of halide PSCs. Thus, this emerging hybrid solar cell has the potential to meet the urgent need for low cost and high efficiency power generation.

The first types of PSCs were similar to liquid electrolyte base dye-sensitized solar cells except that a halide perovskite was used as the light absorber. The power conversion efficiency (PCE) of such devices was about 3.8%. These devices, however, had critical stability problems, since the liquid electrolyte easily dissolved the halide perovskite. Later, the liquid electrolyte was substituted with solid hole transport materials (HTM), 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD), and as a result the PCE of PSCs jumped to 9.7%. More recent developments have dramatically improved the material properties and processing techniques of halide perovskites, leading to the appearance of PSCs with a PCE of 22.1%.

Despite these advantages, the commercialization of halide PSCs is still challenging, due to the poor long-term stability of the halide perovskites. In particular, when halide perovskites are exposed to water, heat or visible light, the halide perovskite phase is dissociated into iodide compounds and by-products. While easy degradation is a pressing and urgent issue, there are relatively few studies on improving the long-term stability of halide PSCs.

One way to increase the stability of PSCs is to modify the perovskite layer. In one example, Br−ions are incorporated to the I−site of methyl ammonium lead iodide (MALI, CH3NH3PbI3) to form a more stable structure than pure MALI. In other examples, new organic-inorganic compositions, such as (PEA)2(MA)2Pb3I10, (5-AVA)x(MA)1-xPbI3, have been tested. In addition, the HTM layer of the solar cells has also been modified to improve the stability of PSCs. In one example, single-wall carbon nanotubes are added to the organic polymer matrix of the HTM to help PSCs maintain their performance at high temperature and humidity. Also, the dopant-free tetrathiafulvalene derivative is reported to enhance the durability of PSCs, since HTM does not contain deliquescent additives such as lithium compounds used in Spiro-OMeTAD.

One more very promising way to circumvent the degradation problem is to coat an additional passivation layer onto the PSC. For example, an Al2O3buffer layer between the perovskite layer and the metal electrode can reduce shunting degradation by inhibiting a direct contact between the metal electrode and the perovskite. Also, when TiO2nanoparticles are coated with a thin oxide shell of Sb2S3, Y2O3, MgO, direct contact between TiO2/perovskite interfaces are blocked and the degradation rate of the perovskite is reduced. Deposition of a hydrophobic polytetrafluoroethylene layer onto the top side of PSCs can also protect the halide perovskite from ambient humidity.

None of these methods, however, have proven to be both effective and commercially viable.

SUMMARY OF THE INVENTION

In one embodiment, an electronic device, such as, without limitation, a perovskite solar cell or a light emitting diode, is provided that includes an assembly including at least one electronic portion or component, and a composite coating layer covering at least part of the assembly including the at least one electronic portion or component. The composite coating layer includes a polymer material (e.g., including an oxygen atom or atoms), such as, without limitation, polymethyl methacrylate (PMMA), polyurethane (PU), or a PMMA-PU mixture, having nanoparticles, such as, without limitation, graphene oxide, reduced graphene oxide, ZnO2, ZrO2, CeO2, SnO2or SiO2, embedded therein. The electronic device may further include a second coating layer including a second polymer material (such as, without limitation, PMMA, PU or PMMA-PU without nanoparticles) positioned between the coating layer and the assembly.

In another embodiment, a method of making an electronic device is provided. The method includes forming an assembly including at least one electronic portion or component, and depositing a composite coating layer over at least part of the assembly including the at least one electronic portion or component, wherein the composite coating layer comprises a polymer material having nanoparticles embedded therein. The method may further include forming a second coating layer including a second polymer material without embedded nanoparticles between the coating layer and the assembly, wherein the coating layer and the second coating layer have different levels of hydrophobicity.

