A method for preparing an amorphous-polycrystalline composite electron transport layer for perovskite solar cells

Abstract

The present invention belongs to the technical field of solar cells, and is a method for preparing an amorphous-polycrystalline composite electron transport layer for a perovskite solar cell. The structure of the perovskite solar cell with the amorphous-polycrystalline composite electron transport layer is, from bottom to top, a substrate, an amorphous-polycrystalline composite electron transport layer, a perovskite light absorption layer, a hole transport layer, and a metal electrode. Compared with the traditional SnO2-based perovskite solar cell, the amorphous-polycrystalline composite electron transport layer is more conducive to electron transport, improves the charge transfer rate, and the electron mobility is increased from the original 7.67*10 ‑4 cm 2 V ‑1 S ‑1 Increased to 1.45*10 ‑3 cm 2 V ‑1 S ‑1 , reducing the charge recombination caused by SnO2 surface defects, the SnO2 surface defect state density from 1.33*10 17 cm ‑3 , reduced to 3.66*10 16 cm ‑3 , the cell photoelectric conversion efficiency increased from 20.15% to 22.17%.

Description

Technical Field

[0001] The invention belongs to the technical field of solar cells and relates to a method for preparing an amorphous-polycrystalline composite electron transport layer. Background Art

[0002] With the rapid development of organic-inorganic hybrid perovskite solar cells, their efficiency has increased from 3.81% in 2009 to the current 25.7% [https: / / www.nrel.gov / pv / cell-efficiency.jpg]. There are many critical issues in the preparation of high-efficiency batteries, such as energy level matching between functional layers, interface contact, surface defects, etc. The electron transport layer mainly transports electrons and blocks holes. The electron transport layer is divided into organic electron transport layer and inorganic electron transport layer. The organic electron transport layer is easy to process,

[0003] The advantages of good performance, but there are disadvantages of poor environmental and photothermal stability, which seriously limits the stability of the entire device. Inorganic electron transport layer, mainly using inorganic metal oxides such as TiO2, but TiO2 has a high catalytic activity, so that the battery device with TiO2 electron transport layer under ultraviolet light, oxygen desorption induces the decomposition of the perovskite layer [Nat. Commun. 2013, 4, 2885]. The bulk electron mobility of TiO2 is <1cm 2 V -1 s -1 , the electron mobility of the film is low (10 -5 cm 2 V -1 s -1 ), the migration rates of electrons and holes in the device are inconsistent, resulting in hysteresis [Nature Energy 2016, 2, 16177]. TiO2 requires a higher heat treatment temperature, which limits the use prospects of TiO2 in flexible devices. In recent years, SnO2 has attracted much attention as the electron transport layer of PSCs. Compared with TiO2, it has the following advantages: 1) It has a deeper conduction band and good energy level matching, which is more conducive to electron extraction and prevention of hole migration at the electron transport layer / perovskite interface; 2) It has a high volume electron mobility (240cm 2 V -1 s -1) and high conductivity, which can improve electron transfer efficiency and reduce recombination losses; 3) It has a wider band gap (3.6-4.0eV) and higher transmittance, ensuring that most light energy passes through and reaches the perovskite layer, reducing the loss of incident light; 4) It can be heat treated at low temperature (<200℃) and can be applied to flexible devices. 5) It has excellent chemical stability and low photocatalytic activity, which is beneficial to the overall long-term stability of the device [Small2018,14,1801154].

[0004] The performance of SnO2 depends largely on the preparation method and processing conditions. The preparation methods mainly include sol-gel method, atomic layer deposition method, chemical bath deposition method, spin coating and other preparation methods, and a planar polycrystalline dense SnO2 electron transport layer is prepared. However, the SnO2 films prepared by these methods are usually amorphous or have low crystallinity, which directly leads to relatively poor electron mobility and conductivity. Highly crystalline SnO2 nanoparticles can effectively overcome this problem and obtain high-quality SnO2 films with almost no traps. However, high-temperature sintering will cause obvious pinholes and traps in the film, which will lead to serious interface recombination and charge transfer barriers, resulting in poor device performance. Due to the poor conductivity of the SnO2 electron transport layer, a large number of traps on the surface, and mismatch with the energy level of the perovskite film, SnO2-based devices still have a certain hysteresis, so SnO2 needs to be modified or post-processed.

[0005] The present invention adopts a simple and effective method to introduce a Ti source into SnO2 under low temperature conditions to form an amorphous-polycrystalline SnO2 composite electron transport layer. This composite electron transport layer is more conducive to charge transport and can passivate SnO2 surface defects to obtain an electron transport layer with better transport performance and smaller interface composite. This has a certain driving effect on the optimization of the electron transport layer and the improvement of the device performance of the perovskite solar cell. Summary of the invention

[0006] The purpose of the present invention is to prepare an amorphous-polycrystalline composite electron transport layer, increase the charge transfer rate, passivate surface defects, and thus improve device performance.

[0007] The technical solution of the present invention:

[0008] A method for preparing an amorphous-polycrystalline composite electron transport layer for a perovskite solar cell, wherein the structure of the perovskite solar cell with the amorphous-polycrystalline composite electron transport layer is, from bottom to top, a substrate, an amorphous-polycrystalline composite electron transport layer, a perovskite light absorption layer, a hole transport layer and a metal electrode;

[0009] Step 1, ultrasonically clean the fluorine-doped tin oxide conductive glass substrate FTO with detergent, deionized water, anhydrous ethanol, and isopropanol for 20-50 minutes respectively;

[0010] Step 2, spin coating an amorphous-polycrystalline composite electron transport layer on the FTO;

[0011] An ammonium fluorotitanate aqueous solution with a concentration of 0.3-1.5 g / L is mixed with a SnO2 aqueous solution in a volume ratio of 1:3-1:5, and placed in a 40-80° C. oven for reaction for 1-3 hours to obtain an ammonium fluorotitanate-SnO2 colloidal dispersion; wherein the SnO2 aqueous solution is a 15% wt colloidal aqueous dispersion; after the reaction is completed, the mixture is shaken for 1 minute and filtered using an organic filter membrane with a pore size of 0.22-0.50 μm;

[0012] The cleaned FTO was treated with UV ozone for 10 to 50 minutes, and the ammonium fluorotitanate-SnO2 colloidal dispersion was dropped in the middle of the substrate, and the dispersion was evenly covered on the substrate using a 4000-5000 rpm / min spin coating process; then, annealed at 100 to 200°C for 20 to 60 minutes to form an amorphous-polycrystalline composite electron transport layer;

[0013] Step 3: deposit the perovskite layer, the hole transport layer Spiro-OMeTAD, and the evaporated metal electrode in sequence; the perovskite layer adopts a two-step spin coating process, first spin coating the PbI2 layer, and then spin coating the organic salt; the hole transport layer adopts dynamic spin coating, and the metal electrode is completed by vacuum evaporation.

[0014] Beneficial effects of the invention: The invention designs a perovskite solar cell with an amorphous-polycrystalline composite electron transport layer. Compared with the blank reference SnO2-based perovskite solar cell, the amorphous-polycrystalline composite electron transport layer is more conducive to electron transport and improves the charge transfer rate. The electron mobility is increased from the original 7.67*10 -4 cm 2 V -1 S -1 Increased to 1.45*10 - 3 cm 2 V -1 S -1 , reducing the charge recombination caused by SnO2 surface defects, the SnO2 surface defect state density from 1.33*10 17 cm -3 , reduced to 3.66*10 16 cm -3 , the cell photoelectric conversion efficiency increased from 20.15% to 22.17%. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 (a) Scanning electron microscope device cross-section of a perovskite solar cell, in which: from bottom to top are glass, conductive glass FTO layer, electron transport layer, perovskite layer, hole transport layer and metal electrode;

[0016] Figure 1 (b) Current-voltage curve of the photoelectric conversion efficiency of the test device based on two electron transport layers;

[0017] Figure 2 (a) is the electron mobility curve of two SnO2 electron transport layers;

[0018] Figure 2 (b) is the defect state density analysis curve of two SnO2 electron transport layers;

[0019] Figure 2 (c) is the relative conductivity curve of the two SnO2 electron transport layers;

[0020] Figure 3 This is the distribution diagram of the photoelectric conversion efficiency of perovskite solar cells based on SnO2 electron transport layers with different doping concentrations. DETAILED DESCRIPTION

[0021] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings and technical solutions.

[0022] Example 1 Preparation of a perovskite solar cell based on an amorphous-polycrystalline composite electron transport layer:

[0023] Take a fluorine-doped tin oxide conductive substrate FTO with a size of 1.9×1.9 cm 2 , ultrasonically cleaned with detergent, deionized water, anhydrous ethanol, and isopropanol for 30 min in sequence, and dried in an oven at 100 °C.

[0024] Preparation of amorphous-polycrystalline composite electron transport layer: First, the ammonium fluorotitanate-SnO2 needs to be heat treated in an oven at 80℃ for 3h, shaken for 1min, and filtered with a 0.22μm organic filter head for use. Take 200μL of ammonium fluorotitanate-SnO2 aqueous solution, drop it on the ozone-treated FTO, evenly coat it at a spin coating speed of 4500rpm / min, and anneal it on a hot plate at 160℃ for 20min to form an amorphous-polycrystalline composite electron transport layer.

[0025] Next, in the N2 glove box, a two-step method was used to prepare the organic-inorganic hybrid perovskite layer, a dynamic spin coating was used to prepare the hole transport layer, and a vacuum evaporation method was used to prepare the metal back electrode. The battery device structure is as follows: Figure 1 (a) shows the efficiency of the manufactured perovskite solar cell device. The current density-voltage curve is shown in Figure 1 (b), the specific optoelectronic parameters are shown in Table 1.

[0026] Table 1. Photoelectric parameters of perovskite solar cells based on different electron transport layers: SnO2 and composite-SnO2

[0027]

[0028] Example 2 Preparation of a perovskite solar cell based on an amorphous-polycrystalline composite electron transport layer at different doping concentrations:

[0029] The size is 1.9×1.9cm 2 The conductive substrate FTO was cleaned with detergent, deionized water, anhydrous ethanol and isopropanol ultrasonically for 30 min in sequence and dried in an oven at 100 °C.

[0030] Preparation of amorphous-polycrystalline composite electron transport layer at different doping concentrations: First, prepare different concentrations of 0.4g / L, 0.7g / L, 1.2g / L, and 1.5g / L ammonium fluorotitanate aqueous solution, heat treat in an oven at 80°C for 3h, shake for 1min, and filter with a 0.22μm organic filter head for use. Take 200μL of ammonium fluorotitanate-SnO2 aqueous solution, drop it on the ozone-treated FTO substrate, evenly coat it on the FTO at a spin coating speed of 4500rpm / min, and anneal on a hot plate at 160°C for 20min to form an amorphous-polycrystalline composite electron transport layer.

[0031] Next, in a nitrogen glove box, a two-step method was used to prepare the organic-inorganic hybrid perovskite layer, a hole transport layer was prepared by dynamic spin coating, and a metal back electrode was prepared by vacuum evaporation. The statistical distribution of the efficiency of the perovskite solar cell device was tested as follows: Figure 3 . With the increase of the concentration of ammonium fluorotitanate aqueous solution, the photoelectric conversion efficiency of the device gradually increased, and reached the best efficiency of 22.17% at a concentration of 1.5g / L. When the concentration continued to increase, the ammonium fluorotitanate-SnO2 mixed solution became colloid and the spin coating process could not be realized. Therefore, 1.5g / L ammonium fluorotitanate aqueous solution was the best doping concentration.

Claims

1. A method for preparing an amorphous-polycrystalline composite electron transport layer for a perovskite solar cell, characterized in that: The structure of the perovskite solar cell with an amorphous-polycrystalline composite electron transport layer is, from bottom to top, a substrate, an amorphous-polycrystalline composite electron transport layer, a perovskite light absorption layer, a hole transport layer, and a metal electrode; Step 1, ultrasonically clean the fluorine-doped tin oxide conductive glass substrate FTO with detergent, deionized water, anhydrous ethanol, and isopropanol for 20-50 minutes respectively; Step 2, spin coating an amorphous-polycrystalline composite electron transport layer on the FTO; An ammonium fluorotitanate aqueous solution with a concentration of 0.3-1.5 g / L is mixed with a SnO2 aqueous solution in a volume ratio of 1:3-1:5, and placed in a 40-80° C. oven for reaction for 1-3 hours to obtain an ammonium fluorotitanate-SnO2 colloidal dispersion; wherein the SnO2 aqueous solution is a 15% wt colloidal aqueous dispersion; after the reaction is completed, the mixture is shaken for 1 minute and filtered using an organic filter membrane with a pore size of 0.22-0.50 μm; The cleaned FTO was treated with UV ozone for 10 to 50 minutes, and the ammonium fluorotitanate-SnO2 colloidal dispersion was dropped in the middle of the substrate, and the dispersion was evenly covered on the substrate using a 4000-5000 rpm / min spin coating process; then, annealed at 100 to 200°C for 20 to 60 minutes to form an amorphous-polycrystalline composite electron transport layer; Step 3: deposit the perovskite layer, the hole transport layer Spiro-OMeTAD, and the evaporated metal electrode in sequence; the perovskite layer adopts a two-step spin coating process, first spin coating the PbI2 layer, and then spin coating the organic salt; the hole transport layer adopts dynamic spin coating, and the metal electrode is completed by vacuum evaporation.

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