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SEMI-TRANSPARENT PEROVSKITE-BASED PHOTOVOLTAIC CELLS AND PROCESS FOR PREPARING THEM

20230232705 · 2023-07-20

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    Abstract

    A semi-transparent perovskite-based photovoltaic cell (or solar cell), wherein the photoactive perovskite layer includes at least one polysaccharide-based inert polymer in an amount ranging between 0.5% by weight and 3.5% by weight, preferably ranging between 1% by weight and 3% by weight, more preferably ranging between 1.5% by weight and 2.8% by weight, with respect to the total weight of the perovskite precursors. The semi-transparent perovskite-based photovoltaic cell (or solar cell) can be advantageously used in various applications that require the production of electricity through the exploitation of light energy, in particular solar radiation energy such as, for example: building integrated photovoltaic (BIPV) systems; photovoltaic windows; greenhouses; photo-bioreactors; noise barriers; lighting; design; advertising; automotive industry. Said semi-transparent perovskite-based photovoltaic cell (or solar cell) can be used either in a “stand alone” mode or in modular systems.

    Claims

    1. A semi-transparent perovskite-based photovoltaic cell (or solar cell), wherein the photoactive perovskite layer comprises at least one polysaccharide-based inert polymer in an amount ranging between 0.5% by weight and 3.5% by weight, with respect to the total weight of the perovskite precursors, said polysaccharide-based inert polymer being selected from methylcellulose, 2-hydroxyethyl cellulose (HEC), methyl-2-hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cellulose acetate phthalate, cellulose propionate, corn starch, potato starch, rice starch, 2-hydroxyethyl starch, carboxymethyl starch, glycogen.

    2. The semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1, wherein said perovskite is selected from organometallic trihalides having general formula ABX.sub.3, wherein: A represents a monovalent organic cation such as methylammonium (CH.sub.3NH.sub.3.sup.+), formamidinium [CH(NH.sub.2).sub.2.sup.+], n-butylammonium (C.sub.4H.sub.12NH.sub.3.sup.+), tetra-butylammonium (C.sub.16H.sub.36N.sup.+), or mixtures thereof; or A represents a monovalent inorganic cation such as caesium (Cs.sup.+, rubidium (Rb.sup.+), potassium (K.sup.+), lithium (Li.sup.+), sodium (Na.sup.+), copper (Cu.sup.+), silver (Ag.sup.+), or mixtures thereof; or mixtures thereof; B represents a divalent metallic cation such as lead (Pb.sup.2+), tin (Sn.sup.2+), or mixtures thereof; and X represents a halide anion such as iodine (I.sup.−), chlorine (Cl.sup.−), bromine (Br.sup.−), or mixtures thereof.

    3. The semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1, wherein said perovskite is selected from: methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3), methylammonium lead bromide (CH.sub.3NH.sub.3PbBr.sub.3), methylammonium lead chloride (CH.sub.3NH.sub.3PbCl.sub.3), methylammonium lead iodide bromide (CH.sub.3NH.sub.3PbI.sub.xBr.sub.3-x), methylammonium lead iodide chloride (CH.sub.3NH.sub.3PbI.sub.xCl.sub.3-x), formamidinium lead iodide [CH(NH.sub.2).sub.2PbI.sub.3], formamidinium lead bromide [CH(NH.sub.2).sub.2PbBr.sub.3], formamidinium lead chloride [CH(NH.sub.2).sub.2PbCl.sub.3], formamidinium lead iodide bromide [CH(NH.sub.2).sub.2PbI.sub.xBr.sub.3-x], formamidinium lead iodide chloride [CH(NH.sub.2).sub.2PbI.sub.xCl.sub.3-x], methylammonium formamidinium lead iodide [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.3-xPbI.sub.3], methylammonium formamidinium lead bromide [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.3-xPbBr.sub.3], methylammonium formamidinium lead chloride [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.3-xPbCl.sub.3], methylammonium formamidinium lead iodide chloride [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.3-xPbI.sub.3-yCl.sub.y], methylammonium formamidinium lead iodide bromide [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.3-xPbI.sub.3-yBr.sub.y], n-butylammonium lead iodide (C.sub.4H.sub.32NH.sub.3PbI.sub.3), tetra-butylammonium lead iodide (C.sub.16H.sub.36NPbI.sub.3), n-butylammonium lead bromide (C.sub.4H.sub.32NH.sub.3PbBr.sub.3), tetra-butylammonium lead bromide (C.sub.16H.sub.36NPbBr.sub.3), caesium lead iodide (CsPbI.sub.3), rubidium lead iodide (RbPbI.sub.3), potassium lead iodide (KPbI.sub.3), caesium methylammonium lead iodide [Cs.sub.x(CH.sub.3NH.sub.3).sub.3-xPbI.sub.3), potassium methylammonium lead iodide [K.sub.x(CH.sub.3NH.sub.3).sub.3-xPbI.sub.3), caesium methylammonium lead iodide chloride [Cs.sub.x(CH.sub.3NH.sub.3).sub.3-xPbI.sub.3-yCl.sub.y), caesium formamidinium lead iodide [Cs.sub.x(CH(NH.sub.2).sub.2).sub.3-xPbI.sub.3], caesium formamidinium lead bromide [Cs.sub.x(CH(NH.sub.2).sub.2).sub.3-xPbBr.sub.3], caesium formamidinium lead iodide chloride [Cs.sub.x(CH(NH.sub.2).sub.2).sub.3-xPbI.sub.3-yCl.sub.y], methylammonium tin iodide (CH.sub.3NH.sub.3SnI.sub.3), methylammonium tin bromide (CH.sub.3NH.sub.3SnBr.sub.3), methylammonium tin iodide bromide (CH.sub.3NH.sub.3SnI.sub.xBr.sub.3-x), formamidinium tin iodide [CH(NH.sub.2).sub.2SnI.sub.3], formamidinium tin iodide bromide [CH(NH.sub.2).sub.2SnI.sub.xBr.sub.3-x], n-butylammonium tin iodide (C.sub.4H.sub.32NH.sub.3SnI.sub.3), tetra-butylammonium tin iodide (C.sub.36H.sub.36NSnI.sub.3), n-butylammonium tin bromide (C.sub.4H.sub.32NH.sub.3SnBr.sub.3), tetra-butylammonium tin bromide (C.sub.16H.sub.36NSnBr.sub.3), methylammonium tin lead iodide (CH.sub.3NH.sub.3Sn.sub.xPb.sub.1-xI.sub.3), formamidinium tin lead iodide [CH(NH.sub.2).sub.2Sn.sub.xPb.sub.1-xI.sub.3], or mixtures thereof; preferably from methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3), formamidinium lead iodide [CH(NH.sub.2).sub.2PbI.sub.3], methylammonium formamidinium lead iodide chloride [(CH.sub.3NH.sub.3).sub.x(CH(NH.sub.2).sub.2).sub.1-xPbI.sub.3-yCl.sub.y], caesium methylammonium lead iodide chloride [Cs.sub.x(CH.sub.3NH.sub.3).sub.1-xPbI.sub.3-yCl.sub.y), caesium formamidinium lead iodide chloride [Cs.sub.x(CH(NH.sub.2).sub.2).sub.1-xPbI.sub.3-yCl.sub.y].

    4. The semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1, wherein said polysaccharide-based inert polymer is selected from 2-hydroxyethyl cellulose (HEC), cellulose acetate phthalate, corn starch.

    5. The semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1, comprising: a glass substrate covered with a layer of transparent and conductive oxide (TCO), commonly fluorine-doped tin oxide (SnO.sub.2:F) (FTO), or indium tin oxide (ITO) which constitutes the anode; a layer based on a hole transport material (“Hole Transport Layer”—HTL), preferably a layer of poly[bis(4-phenyl(2,4,6-trimethylphenyl)amine (PTAA), or a layer of poly[bis(4-butylphenyl)-bisphenylbenzidine] (Poly-TPD), or a layer of a mixture of poly(3,4-ethylenedioxythiophene) and polystyrene sulfonate (PEDOT:PSS); optionally, a layer based on a material to improve the wettability, preferably a layer of poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7fluorene)-alt-2,7-(9,9-dioctylfluorene))-dibromide (PFN-Br); a photoactive layer comprising at least one perovskite, preferably methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3), and at least one inert polymer based on cellulose or starch, preferably 2-hydroxyethyl cellulose (HEC); a layer based on an electron transport material (“Electron Transport Layer”-ETL), preferably a layer of methyl ester of the [6,6]-phenyl-C.sub.61-butyric acid (PC.sub.61BM); optionally a layer based on a hole blocking material (“Hole Blocking Layer”—HBL), preferably a layer of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine—BCP) or ethoxylated polyethylenimine (PEIE); a metallic contact known as “back contact” which constitutes the cathode.

    6. The semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1, wherein the electrical energy generated by said at least one semi-transparent perovskite-based photovoltaic cell (or solar cell) is transported using a wiring system which is connected with said semi-transparent perovskite-based photovoltaic cell (or solar cell).

    7. A process for preparing a semi-transparent perovskite-based photovoltaic cell (or solar cell) comprising the following steps: (a) preparing a glass substrate covered with a layer of transparent and conductive oxide (TCO) (anode); (b) depositing a layer based on a hole transport material (“Hole Transport Layer”—HTL) on the substrate obtained in said step (a); (c) optionally, depositing on the layer based on a hole transport material (“Hole Transport Layer”—HTL) obtained in said step (b) a layer based on a material to improve the wettability; (d) preparing a mixture comprising perovskite precursors and at least one inert polymer based on cellulose or starch, said inert polymer being used in an amount ranging between 0.5% by weight and 3.5% by weight, preferably ranging between 1% by weight and 3% by weight, more preferably ranging between 1.5% by weight and 2.8% by weight, with respect to the total weight of the perovskite precursors; (e) depositing the mixture obtained in said step (d) on the layer based on a hole transport material (“Hole Transport Layer”—HTL) obtained in said step (b), or on the layer based on a material to improve the wettability obtained in said step (c), obtaining a photoactive layer; (f) depositing a layer based on an electron transport material (“Electron Transport Layer”—ETL), on the photoactive layer obtained in said step (e); (g) optionally, depositing on the layer based on an electron transport material (“Electron Transport Layer”—ETL) obtained in said step (g), a layer based on a hole blocking material (“Hole Blocking Layer”—HBL); and (h) depositing a metallic contact known as “back contact” which constitutes the cathode, on the layer based on an electron transport material (“Electron Transport Layer”—ETL) obtained in said step (f), or on the layer based on a hole blocking material (“Hole Blocking Layer”—HBL) obtained in said step (g); wherein said steps (b), (c), (e), (f) and (g), are carried out at a temperature lower than 120° C.

    8. A use of a semi-transparent perovskite-based photovoltaic cell (or solar cell) according to claim 1: architecturally integrated photovoltaic systems (“Building Integrated Photo Voltaic”—BIPV); photovoltaic windows; greenhouses; photo-bioreactors; noise barriers; lighting; design; advertising; automobile industry.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0065] The present disclosure will now be illustrated in greater detail through an embodiment with reference to FIG. 1 reported below.

    DETAILED DESCRIPTION OF THE DRAWINGS

    [0066] In particular, FIG. 1 depicts a cross-sectional view of a semi-transparent perovskite-based photovoltaic cell (or solar cell) (1) comprising the following layers: a glass substrate (7) covered with a transparent, conductive oxide (TCO) layer (anode) [e.g., indium tin oxide (“Indium Tin Oxide”—ITO) or fluorine-doped tin oxide (SnO.sub.2:F) (“Fluorine-doped Tin Oxide”—FTO)] (2); a layer based on a hole transport material (“Hole Transport Layer”—HTL) (e.g., poly[bis(4-phenyl(2,4,6-trimethylphenyl)amine (PTAA), poly[bis(4-butylphenyl)-bisphenylbenzidine] (Poly-TPD), or a mixture of poly(3,4-ethylenedioxythiophene and polystyrene sulfonate (PEDOT:PSS) (3); optionally a layer based on a wettability enhancing material, [e.g., poly(9,9-bis(3′-(N,N-dimethyl)-N-ethylammonium-propyl-2,7fluorene)-alt-2,7-(9,9-dioctylfluorene))-dibromide (PFN-Br)] (not shown in FIG. 1); a photoactive layer comprising at least one perovskite [e.g., methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3) and at least one polysaccharide-based inert polymer [e.g., 2-hydroxyethyl cellulose (HEC)] (4); a layer based on an electron transport material [“Electron Transport Layer” (ETL)] [e.g., methyl ester of the [6,6]-phenyl-C.sub.61-butyric acid (PC.sub.61BM)] (5a); a layer based on a hole blocking material (“Hole Blocking Layer” (HBL) [e.g., 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (Batocuproin—BCP) or polyethyleneimine ethoxylate (PEIE)] (5b); a metallic contact known as a “back contact” which constitutes the cathode [e.g., a gold, silver, or metallic aluminium layer] (6).

    [0067] In order to better understand the present disclosure and to put it into practice, some illustrative and non-limiting examples thereof are reported below.

    [0068] In the following examples, for the sake of simplicity, the term “solar cell” is used, which is to be intended to have the same meaning as “photovoltaic cell”.

    EXAMPLE 1

    Preparation of a Semi-Transparent Perovskite-Based Photovoltaic Cell

    [0069] For this purpose, a perovskite-based solar cell was prepared on a glass substrate coated with ITO [Indium Tin Oxide (Kintec KT18086-1)] and patterned (dimensions 15×15×1 mm; sheet resistance equal to 12 Ω/cm.sup.2) and previously subjected to a cleaning process consisting of manual cleaning by wiping with a lint-free cloth soaked in a detergent diluted with deionized water. The substrate was then rinsed with deionized water. Subsequently, the substrate was thoroughly cleaned using the following methods in sequence: ultrasonic baths in (i) deionized water plus detergent (followed by manual drying with a lint-free cloth); (ii) distilled water [followed by manual drying with a lint-free cloth]; (iii) acetone (Aldrich) and (iv) iso-propanol (Aldrich) in sequence. In particular, the substrate was placed in a beaker containing the solvent, placed in an ultrasonic bath, kept at 40° C., for a treatment of 10 minutes. After treatments (iii) and (iv), the substrate was dried with a compressed nitrogen flow.

    [0070] Subsequently, the glass/ITO was further cleaned by treatment in an ozone device (UV Ozone Cleaning System EXPO3—Astel), immediately before proceeding to the next step.

    [0071] The substrate thus treated was ready for the deposition of the layer based on a hole transport material (“Hole Transport Layer”—HTL). For this purpose, a solution of poly[bis(4-phenyl)(2,4,6-trimethyl)amine (PTTA) (Aldrich) in toluene (99.5% purity—Aldrich) at a concentration equal to 1.5 mg/ml, was deposited by spin coating, operating at a rotation speed equal to 6000 rpm (acceleration equal to 500 rpm/s), for 30 seconds: the whole was subjected to heat treatment (annealing), at 100° C., for 10 minutes. The thickness of the layer based on a hole transport material (“Hole Transport Layer”—HTL) was found to be equal to 40 nm.

    [0072] The substrate thus obtained was placed in a dry box and the layer of methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3) and 2-hydroxyethyl cellulose (HEC) was deposited on the layer based on a hole transport material (“Hole Transport Layer”—HTL), operating as follows. For this purpose, lead iodide (PbI.sub.2) (purity 99.9985%—Alfa Aesar) (305.5 mg-0.66 mmoles), methylammonium iodide (MAI) (CH.sub.3NH.sub.3I) (GreatCell Solar) (104.3 mg-0.66 mmoles) and 2-hydroxyethyl cellulose (HEC) (weight average molecular weight (M.sub.w)=250000) (Aldrich) (10.2 mg), previously dried in an oven, for 5 days, so that the water content is less than 2% by weight, were dissolved in anhydrous dimethyl sulfoxide (purity 99.9%—Aldrich) (1 ml), while stirring at a temperature of 80° C., for 3 hours, obtaining a solution containing 27% by weight of perovskite precursors and 0.66% by weight of 2-hydroxyethyl cellulose (HEC), i.e. 2.5% by weight of 2-hydroxyethyl cellulose (HEC) with respect to the total weight of the other solid components (i.e. lead (PbI.sub.2)+methylammonium iodide (MAI) (CH.sub.3NH.sub.3I). The solution thus obtained has been deposited on said layer based on a hole transport material (“Hole Transport Layer”—HTL), by spin coating operating at a rotation speed equal to 12000 rpm (acceleration equal to 1000 rpm/s), for 60 seconds and the whole has been subjected to heat treatment (annealing), at 100° C., for 60 minutes. The thickness of the perovskite and 2-hydroxyethyl cellulose (HEC) layer was found to be equal to 170 nm.

    [0073] The substrate thus obtained was ready for the deposition of the layer based on an electron transport material (“Electron Transport Layer”—ETL). For this purpose, a filtered solution of methyl ester of [6,6]-phenyl-C.sub.61-butyric acid (PC.sub.61BM) (Nano-C Products) (25 mg) in anhydrous chlorobenzene (purity 99.8%—Aldrich) (1 ml), was deposited, by spin coating operating at a rotation speed equal to 1000 rpm (acceleration equal to 500 rpm/s), for 60 seconds: the substrate obtained was allowed to rest, at room temperature (25° C.), for 5 minutes. The thickness of the layer based on an electron transport material (“Electron Transport Layer”—HTL) was found to be equal to 50 nm.

    [0074] The substrate thus obtained was ready for the deposition of a layer based on a hole blocking material (“Hole Blocking Layer”—HBL). For this purpose, a solution of 2,9-dimethyl-4,7-diphenyl-1,10-phenatroline (Batocuproin—BCP) (purity 96%—Aldrich) (5 mg) in anhydrous iso-propyl alcohol (purity 99.5%-Aldrich) (10 ml) obtained by operating under stirring at 80° C., for 3 hours, was deposited, by spin coating operating at a rotation speed equal to 6000 rpm (acceleration equal to 1000 rpm/s), for 20 seconds: the substrate obtained was allowed to rest, at room temperature (25° C.), for 5 minutes. The thickness of the layer based on a hole blocking material (“Hole Blocking Layer”—HBL) was found to be equal to 5 nm.

    [0075] Subsequently, gold (Au) “back contact” (cathode) was deposited on said layer based on a hole blocking material (“Hole Blocking Layer”—HBL) by evaporation. For this purpose, a Kurt J. Lesker evaporator was used, operating at a pressure equal to 2×10.sup.−6 mmHg and a speed equal to 0.2 Angstrom/sec, suitably masking the area of the solar cell so as to obtain an active area equal to 4 mm.sup.2. The thickness of the gold (Au) “back contact” (cathode) was found to be equal to 10 nm.

    [0076] Thicknesses were measured by scanning electron microscopy using a Jeol 7600f Scanning Electron Microscope (SEM), equipped with a field emission electron gun, operating at an accelerating voltage ranging between 1 kV and 5 kV, and exploiting the signal from secondary electrons.

    [0077] The electrical characterization of the obtained semi-transparent perovskite-based solar cell was carried out at room temperature (25° C.). The current-voltage density (J-V) curves were acquired with a Keithley® 2400 sourcemeter connected to a personal computer for data collection. The photocurrent was measured by exposing the solar cell to the light of a Newport 91160A solar simulator (Newport Corp), placed at a distance of 10 mm from said semi-transparent solar cell, equipped with a 300 W Xenon light source, using an illumination spot equal to 100 mm×100 mm: Table 1 shows the characteristic parameters as average values.

    [0078] The light intensity was calibrated with a standard silicon solar cell (“VLSI Standard”—SRC-100-RTD-KG5).

    [0079] In addition, said semi-transparent perovskite-based solar cell was subjected to the measurement of transparency in the visible region [“Average Visible Transmittance”—(AVT)] (i.e. AVT>20%), measured in the range between 400 nm and 800 nm, using a UV-vis spectrophotometer (VarianAU/DN{circumflex over ( )}MS-100s): the measurement was carried out both on the complete semi-transparent solar cell based on perovskite, and on the semi-transparent perovskite-based photovoltaic cell before the deposition of the gold (Au) back contact (cathode): Table 1 reports the results obtained as average values.

    [0080] In particular, Table 1 reports, in order: the number of the Reference Example; the composition of the photoactive layer based on perovskite and 2-hydroxyethylcellulose; FF (“Fill Factor”); Voc (“Open Circuit Voltage”); Jsc (“short-circuit photocurrent density”); PCE (“Power Conversion Efficiency”); AVT (“Average Visible Transmittance”) (complete solar cell and solar cell without gold cathode).

    EXAMPLE 2

    Preparation of a Semi-Transparent Perovskite-Based Photovoltaic Cell

    [0081] The semi-transparent perovskite-based solar cell was obtained using the same process as reported in Example 1, with the only difference resulting from the use of perovskite precursors and 2-hydroxyethyl cellulose (HEC) in different concentrations.

    [0082] For this purpose, lead iodide (PbI.sub.2) (purity 99.9985%—Alfa Aesar) (272.6 mg-0.59 mmoles), methylammonium iodide (MAI) (CH.sub.3NH.sub.3I) (GreatCell Solar) (94 mg-0.66 mmoles) and 2-hydroxyethyl cellulose (HEC) (weight average molecular weight (M.sub.W)=250000) (Aldrich) (9.2 mg), previously dried in an oven, for 5 days, so that the water content is less than 2% by weight, were dissolved in anhydrous dimethyl sulfoxide (purity 99.9%—Aldrich) (1 ml), while stirring at a temperature of 80° C., for 3 hours, obtaining a solution containing 25% by weight of perovskite precursors and 0.62% by weight of 2-hydroxyethyl cellulose (HEC), i.e. 2.5% by weight of 2-hydroxyethyl cellulose (HEC) with respect to the total weight of the other solid components (i.e. lead (PbI.sub.2)+methylammonium iodide (MAI) (CH.sub.3NH.sub.3I). The solution thus obtained has been deposited on said layer based on a hole transport material (“Hole Transport Layer”—HTL), by spin coating operating at a rotation speed equal to 12000 rpm (acceleration equal to 1000 rpm/s), for 60 seconds and the whole has been subjected to heat treatment (annealing), at 100° C., for 60 minutes. The thickness of the perovskite and 2-hydroxyethyl cellulose (HEC) layer was found to be equal to 120 nm.

    [0083] The electrical characterization of the obtained semi-transparent perovskite-based solar cell was carried out as described above: Table 1 reports the characteristic parameters as average values.

    EXAMPLE 3

    Preparation of a Semi-Transparent Perovskite-Based Photovoltaic Cell

    [0084] The semi-transparent perovskite-based solar cell was obtained using the same process as reported in Example 1, with the only difference resulting from the use of perovskite precursors and 2-hydroxyethyl cellulose (HEC) in different concentrations.

    [0085] For this purpose, lead iodide (PbI.sub.2) (purity 99.9985%—Alfa Aesar) (204.5 mg-0.44 mmoles), methylammonium iodide (MAI) (CH.sub.3NH.sub.3I) (GreatCell Solar) (70.5 mg-0.44 mmoles) and 2-hydroxyethyl cellulose (HEC) (weight average molecular weight (M.sub.W)=250000) (Aldrich) (6.9 mg), previously dried in an oven, for 5 days, so that the water content is less than 2% by weight, were dissolved in anhydrous dimethyl sulfoxide (purity 99.9%—Aldrich) (1 ml), while stirring at a temperature of 80° C., for 3 hours, obtaining a solution containing 20% by weight of perovskite precursors and 0.5% by weight of 2-hydroxyethyl cellulose (HEC), i.e. 2.5% by weight of 2-hydroxyethyl cellulose (HEC) with respect to the total weight of the other solid components (i.e. lead (PbI.sub.2)+methylammonium iodide (MAI) (CH.sub.3NH.sub.3I). The solution thus obtained has been deposited on said layer based on a hole transport material (“Hole Transport Layer”—HTL), by spin coating operating at a rotation speed equal to 12000 rpm (acceleration equal to 1000 rpm/s), for 60 seconds and the whole has been subjected to heat treatment (annealing), at 100° C., for 60 minutes. The thickness of the perovskite and 2-hydroxyethyl cellulose (HEC) layer was found to be equal to 80 nm.

    [0086] The electrical characterization of the obtained semi-transparent solar cell was carried out as described above: Table 1 reports the characteristic parameters as average values.

    EXAMPLE 4 (COMPARATIVE)

    Preparation of a Semi-Transparent Perovskite-Based Photovoltaic Cell

    [0087] The semi-transparent perovskite-based solar cell was obtained using the same process as reported in Example 1, with the only difference resulting from the use of cellulose acetate (CAc) instead of 2-hydroxyethyl cellulose (HEC) and of perovskite precursors in different concentrations.

    [0088] For this purpose, lead iodide (PbI.sub.2) (purity 99.9985%—Alfa Aesar) (350.5 mg-0.75 mmoles), methylammonium iodide (MAI) (CH.sub.3NH.sub.3I) (GreatCell Solar) (120.8 mg-0.75 mmoles) and cellulose acetate (CAc) (weight average molecular weight (M.sub.W)=50000) (Aldrich) (11.8 mg), previously dried in an oven, for 5 days, so that the water content is less than 2% by weight, were dissolved in anhydrous dimethyl sulfoxide (purity 99.9%—Aldrich) (1 ml), while stirring at a temperature of 80° C., for 3 hours, obtaining a solution containing 30% by weight of perovskite precursors and 0.74% by weight of cellulose acetate (CAc), i.e. 2.5% by weight of cellulose acetate (CAc) with respect to the total weight of the other solid components (i.e. lead (PbI.sub.2)+methylammonium iodide (MAI) (CH.sub.3NH.sub.3I). The solution thus obtained has been deposited on said layer based on a hole transport material (“Hole Transport Layer”—HTL), by spin coating operating at a rotation speed equal to 12000 rpm (acceleration equal to 1000 rpm/s), for 60 seconds and the whole has been subjected to heat treatment (annealing), at 100° C., for 60 minutes. The thickness of the perovskite and cellulose acetate (CAc) layer was found to be equal to 250 nm.

    [0089] The electrical characterization of the obtained semi-transparent solar cell was carried out as described above: Table 1 reports the characteristic parameters as average values.

    EXAMPLE 5 (COMPARATIVE)

    Preparation of a Semi-Transparent Perovskite-Based Photovoltaic Cell

    [0090] The semi-transparent perovskite-based solar cell was obtained using the same process as reported in Example 1, with the only difference resulting from the use of hydroxypropyl cellulose (HPC) instead of 2-hydroxyethyl cellulose (HEC) and of perovskite precursors in different concentrations.

    [0091] For this purpose, lead iodide (PbI.sub.2) (purity 99.9985%—Alfa Aesar) (272.6 mg-0.59 mmoles), methylammonium iodide (MAI) (CH.sub.3NH.sub.3I) (GreatCell Solar) (94.0 mg-0.59 mmoles) and hydroxypropyl cellulose (HPC) (weight average molecular weight (M.sub.W)=80000) (Aldrich) (4.0 mg), previously dried in an oven, for 5 days, so that the water content is less than 2% by weight, were dissolved in anhydrous dimethyl sulfoxide (purity 99.9%—Aldrich) (1 ml), while stirring at a temperature of 80° C., for 3 hours: it was not possible to obtain an homogeneous solution and, consequently, to made the semi-transparent perovskite-based solar cell.

    TABLE-US-00001 TABLE 1 Photoactive layer FF.sup.(1) Voc.sup.(2) Jsc.sup.(3) PCE.sup.(4) AVT.sup.(5a) AVT.sup.(5b) Example (thickness - nm) (%) (V) (mA/cm.sup.2) (%) (%) (%) 1 MAPI (27).sup.(6) + HEC (2.5).sup.(7) (170) 67.5 1.02 17.3 12.0 21 36 2 MAPI (25).sup.(6) + HEC (2.5).sup.(7) (120) 72.0 1.06 15.0 11.4 22 39 3 MAPI (20).sup.(6) + HEC (2.5).sup.(7) (80) 66.5 1.02 10.9 7.4 25 47 4 MAPI (30).sup.(6) + CAc (2.5).sup.(8) (250) 50.7 0.44 1.7 0.4 — — (comparative) .sup.(1)“Fill Factor”; .sup.(2)“Open Circuit Voltage”; .sup.(3)“short-circuit photocurrent density”; .sup.(4)“Power Conversion Efficiency”; .sup.(5a)“Average Visible Transmittance” (complete semi-transparent solar cell based on perovskite); .sup.(5b)“Average Visible Transmittance” (semi-transparent perovskite-based solar cell without gold cathode); .sup.(6)methylammonium lead iodide [(CH.sub.3NH.sub.3)PbI.sub.3] [(in brackets % by weight of perovskite precursors (i.e. lead (PbI.sub.2) + methylammonium iodide (MAI) (CH.sub.3NH.sub.3I)]; .sup.(7)2-Hydroxyethyl cellulose (HEC) (in brackets, % by weight of 2-hydroxyethyl cellulose (HEC) with respect to the total weight of the other solid components (i.e., lead (PbI.sub.2) + methylammonium iodide (MAI) (CH.sub.3NH.sub.3I)]; .sup.(8)cellulose acetate (CAc) (in brackets, % by weight of cellulose acetate (CAc) with respect to the total weight of the other solid components (i.e., lead (PbI.sub.2) + methylammonium iodide (MAI) (CH.sub.3NH.sub.3I)].

    [0092] From the data shown in Table 1, it can be seen that the semi-transparent perovskite-based solar cell object of the present disclosure (Example 1-3) has both good power conversion efficiency (PCE) (i.e. PCE>10%), and a good transparency in the visible region [“Average Visible Transmittance”—(AVT)] (i.e. AVT>20%) (measured in the range between 400 nm and 800 nm, this result being obtained without negatively affecting the remaining electrical properties, i.e. the values of FF (“Fill Factor”), Voc (“Open Circuit Voltage”); Jsc (“short-circuit photocurrent density”). On the contrary, the semi-transparent perovskite-based solar cell of Example 4 (comparative) has a very low power conversion efficiency (PCE) (i.e. PCE=0.4%), and poor electrical properties, i.e. the values of FF (“Fill Factor”), Voc (“Open Circuit Voltage”); Jsc (“short-circuit photocurrent density”).