A perovskite solar cell structure with a gradient bandgap hole transport layer

Abstract

The present invention discloses a perovskite solar cell structure with a gradient bandgap hole transport layer. At the interface between the hole transport layer and the perovskite material, the conduction band offset (CBO) is positive, and the valence band offset (VBO) is 0.09 eV - 0.3 eV. The conduction band and valence band at the contact interface with the perovskite material are gradually raised to the contact interface with the back electrode. The electric field formed by the hole transport layer with a gradient bandgap in the present invention is beneficial to transporting the photo-generated holes to the back electrode. The positive CBO generates a peak at the interface between the perovskite layer and the hole layer, which can effectively prevent the electrons in the hole layer from transporting to the perovskite layer, reducing the recombination with the photo-generated holes in the perovskite layer, thereby being beneficial to reducing the recombination current and increasing the open-circuit voltage. The slightly positive VBO can not only ensure that the photo-generated holes in the perovskite material can effectively tunnel into the hole transport layer, but also reduce the recombination of holes. Compared with the uniform bandgap, the conversion efficiency of the structure described in the present invention is significantly improved.

Description

Technical Field

[0001] The present invention relates to a photovoltaic device, and particularly to a perovskite solar cell structure having a gradient bandgap hole transport layer. Background Art

[0002] Perovskite solar cells have been widely studied in the past decade due to their wide light absorption range, direct bandgap structure, small effective masses of photo-generated electrons and holes, very high carrier mobilities of electrons and holes, long carrier diffusion lengths, low exciton binding energy, simple preparation method, and low cost. The photoelectric conversion efficiency of its single-junction cells has increased from 3.8% in 2009 to 25.7% in 2022, far higher than thin-film solar cells such as CIGS / CZTS / CdTe. Although perovskite solar cells have developed rapidly, there are still many problems to be solved urgently. Perovskite solar cells are unstable when placed in air for a long time, mainly because in a humid environment, the perovskite lattice structure will decompose rapidly. Solving the problem of poor stability of perovskite solar cells is an important topic. By using a hydrophobic inorganic hole transport layer material to isolate the perovskite layer material from contact with air, its stability can be improved. Therefore, seeking a new type of hole transport layer material that is cheap, has good stability, and can be comparable to or even better than spiro-OMeTAD is one of the important research directions of perovskite solar cells. Currently, there have been relevant reports that inorganic hole transport layer materials such as CuSCN, CuI, Cu 2 O, PbS, NiO, etc. are applied in perovskite solar cells and show excellent performance, greatly improving the stability of perovskite solar cells under light.

[0003] Copper-based chalcopyrite semiconductor materials have many excellent properties. By adjusting the element ratio, the bandgap range can be adjusted to vary between 1.02 - 3 eV, with a very wide solar light absorption spectrum range, a direct bandgap, and a high light absorption coefficient. They can not only be used as absorption layer materials in thin-film solar cells but also as hole transport layer materials in perovskite solar cells. The chalcopyrite semiconductor material CuIn 0.1 Ga 0.9 (S 0.9 Se 0.1 ) 2 is applied to a perovskite solar cell to obtain a conversion efficiency of 9.15% (Lu Xu, Lin-Long Deng, Jing Cao, Xin Wang, Wei-Yi Chen and Zhiyuan Jiang, Solution-Processed Cu(In,Ga)(S,Se) 2Nanocrystal as Inorganic Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells, Nanoscale Research Letters (2017) 12:159), CuInSe 2 As a hole transport layer applied to perovskite solar cells, it achieved an efficiency of 12.8% (Yan Zhang, Zhenlong Zhanga, Yanyan Liu, Yuefeng Liu, Huiping Gao, Yanli Mao, An inorganic hole-transport material of CuInSe 2 for stable and efficient perovskite solar cells, Organic Electronics 67 (2019) 168 - 174). CuIn 1-x Ga x Se 2 As a hole transport layer applied to perovskite solar cells, it obtained the highest efficiency of 14.2% for perovskite cells with chalcopyrite materials as the hole layer so far (Liann-Be Chang, Chzu-Chiang Tseng, Gwomei Wu, Wu-Shiung Feng, Ming-Jer Jeng, Lung-Chien Chen, Kuan-Lin Lee, Ewa Popko, Lucjan Jacak and Katarzyna Gwozdz, Low-Cost CuIn1-xGa x Se 2 Ultra-Thin Hole-Transporting Material Layer for Perovskite / CIGSe Heterojunction Solar Cells, Appl. Sci. 2019, 9, 719), but it is still far lower than the efficiency of cells with spiro-OMeTAD as the hole layer. Improving the efficiency of perovskite solar cells based on inorganic hole transport layers is an important research topic at present. Summary of the Invention

[0004] To solve the above technical problems and better improve the conversion efficiency of perovskite solar cells with inorganic chalcopyrite materials as the hole transport layer, we provide a perovskite solar cell structure. By designing and implementing a hole transport layer with a gradient bandgap to adjust the conduction band and valence band of the hole transport layer to form an electric field, and at the same time, a better conduction band offset and valence band offset are formed at the interface to further promote the effective separation of photo-generated electrons and holes at the interface, help the collection of carriers, reduce the recombination of carriers, and improve the cell efficiency. Designing a suitable inorganic hole transport layer material with a gradient bandgap, and at the same time considering that the conduction band offset and valence band offset at the interface have a great impact on the stability and photoelectric conversion efficiency of perovskite solar cells. Ensuring that the conduction band offset at the hole layer / perovskite layer interface is positive and the valence band offset is about +0.09 - 0.3 eV can significantly improve the conversion efficiency compared to perovskite cells with an inorganic chalcopyrite hole transport layer with a uniform bandgap.

[0005] The technical solution of the present invention is as follows:

[0006] A perovskite solar cell structure with a hole transport layer having a gradient bandgap, the hole transport layer having a gradient bandgap, and the bandgap width of the contact interface between the hole transport layer and the perovskite material being smaller than the bandgap width of the contact interface between the hole transport layer and the back electrode;

[0007] The bottom of the conduction band and the top of the valence band of the hole transport layer are gradually raised from the contact interface with the perovskite material to the contact interface with the back electrode;

[0008] The valence band offset VBO at the interface between the hole transport layer and the perovskite material is positive, and the conduction band offset CBO at the interface between the hole transport layer and the perovskite material is positive.

[0009] Furthermore, the bandgap width of the hole transport layer at the interface with the perovskite is smaller than the bandgap width of the perovskite material.

[0010] Furthermore, the change range of the valence band offset VBO at the interface between the hole transport layer and the perovskite material is 0.09 eV - 0.3 eV.

[0011] Furthermore, the bottom of the conduction band of the hole transport layer is lower than the perovskite material at the contact interface with the perovskite material, and the top of the valence band of the hole transport layer is lower than the perovskite material at the contact interface with the perovskite material.

[0012] The photovoltaic characteristics of the above perovskite solar cells, including open circuit voltage, short circuit current, fill factor, conversion efficiency, and carrier recombination current characteristics, are simulated and verified by SCAPS software.

[0013] The beneficial effects of the present invention are as follows:

[0014] The perovskite solar cell with a gradient bandgap hole transport layer of the present invention can ensure that the conduction band offset CBO is positive and the valence band offset VBO is 0.09 eV - 0.3 eV at the interface between the hole transport layer and the perovskite material, while the conduction band and valence band at the contact interface with the perovskite material are gradually raised to the contact interface with the back electrode. The electric field formed by the gradient bandgap hole transport layer is beneficial to transporting the photo-generated holes to the back electrode. The positive CBO can effectively prevent the electrons in the hole layer from transporting to the perovskite layer, reducing the recombination with the photo-generated holes in the perovskite layer, thereby reducing the recombination current and increasing the open circuit voltage. The slightly positive VBO can not only ensure the effective tunneling of the photo-generated holes in the perovskite material to the hole transport layer, but also reduce the recombination of holes. Taking CuIn 1- x Ga x Se 2 , Cu 2 Zn(Sn 1-x Ge x )S 4 , Cu 2 ZnSn(Se 1-x S x ) 4 as an example, when CuIn 1-x Ga x Se 2 is used as the hole transport layer material, CBO = 0.7 eV, VBO = 0.021 eV, the bandgap width at the contact interface with the perovskite is 1.06 eV, and the bandgap width at the contact interface with the back electrode is 1.292 eV, a conversion efficiency far greater than 18.32% in the case of a uniform bandgap can be obtained. When Cu 2 ZnSn(Se 1-x S x ) 4 is used as the hole transport layer material, CBO = 0.525 eV, VBO = 0.175 eV, the bandgap width at the contact interface with the perovskite is 1.094 eV, and the bandgap width at the contact interface with the back electrode is 1.2 eV, a conversion efficiency far greater than 19.81% in the case of a uniform bandgap can be obtained.

[0015] The present invention explores an effective method to improve the stability and efficiency of perovskite solar cells based on inorganic hole transport layer materials, providing effective theoretical guidance for experimental work. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Comparison of simulation and experimental data of perovskite cells simulated with Sprio-OMeTAD as the hole layer

[0017] Figure 2 Constructing a simulated gradient bandgap CuIn 1-x Ga x Se2 Schematic diagram of the perovskite solar cell structure with a hole transport layer.

[0018] Figure 3 Example 1 Gradient bandgap CuIn 1-x Ga x Se 2 Energy band diagram of the hole transport layer.

[0019] Figure 4 Example 1 CuIn with different Ga contents 1-x Ga x Se 2 Energy band diagram of the interface in contact with the perovskite material.

[0020] Figure 5 Example 1 CuIn with different Ga contents 1-x Ga x Se 2 Energy band diagram of VBO at the interface in contact with the perovskite material.

[0021] Figure 6 Example 1 Simulating different gradient bandgap CuIn 1-x Ga x Se 2 Contour map of the conversion efficiency of the perovskite solar cell with a hole transport layer.

[0022] Figure 7 Example 1 Simulating different gradient bandgap CuIn 1-x Ga x Se 2 Contour map of the open circuit voltage of the perovskite solar cell with a hole transport layer.

[0023] Figure 8 Example 1 Simulating different gradient bandgap CuIn 1-x Ga x Se 2 Contour map of the short circuit current of the perovskite solar cell with a hole transport layer.

[0024] Figure 9 Example 1 Simulating different gradient bandgap CuIn 1-x Ga x Se 2 Contour map of the fill factor of the perovskite solar cell with a hole transport layer. Detailed implementation manners

[0025] The technical solutions of the present invention will be further described and illustrated below in conjunction with the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] (1) CuIn with a gradient bandgap 1-x Gax Se 2 The hole transport layer has a band gap of 1.02 eV at the contact interface with the perovskite material and a band gap of 1.2 eV at the contact interface with the back electrode.

[0028] (2)CuIn 1-x Ga x Se 2 The bottom of the conduction band and the top of the valence band of the hole transport layer material gradually rise from the contact interface with the perovskite material to the contact interface with the back electrode.

[0029] (3)CuIn 1-x Ga x Se 2 The valence band offset VBO at the interface between the hole transport layer and the perovskite material is positive, with a value of 0.21 eV.

[0030] (4) The conduction band offset CBO at the interface between the hole transport layer and the perovskite material is positive, with a value of 0.7 eV.

[0031] The simulated CuIn with a gradient band gap 1-x Ga x Se 2 The open-circuit voltage of the perovskite solar cell with the hole transport layer is 0.97 eV, the short-circuit current is 23.29 mA / cm2, the fill factor is 81.29%, and the conversion efficiency is 18.32%. Compared with the existing uniform band gap CuIn 1-x Ga x Se 2 The highest reported conversion efficiency of the perovskite solar cell with the hole layer is 14.2% (Liann-Be Chang, Chzu-Chiang Tseng, Gwomei Wu, Wu-Shiung Feng, Ming-Jer Jeng, Lung-Chien Chen, Kuan-Lin Lee, Ewa Popko, Lucjan Jacak and Katarzyna Gwozdz, Low-Cost CuIn1-xGaxSe2 Ultra-Thin Hole-Transporting Material Layer for Perovskite / CIGSe Heterojunction Solar Cells, Appl. Sci. 2019, 9, 719). It is increased by 4.12%, with an increase amplitude of up to 29%, indicating a significant improvement effect.

[0032] The gradient band gap CuIn used in the simulation of this embodiment 1-x Ga x Se 2The parameters of each layer of the perovskite solar cell with a hole transport layer are shown in Table 1, and the parameter sources are experimental theoretical literature reports.

[0033] Table 1

[0034]

[0035] To confirm the effectiveness of the parameters used in the simulation, we simulated the perovskite solar cell with Sprio-OMeTAD as the hole layer and compared it with the experimental reports. The comparison is as Figure 1 shown. The results show that the photovoltaic parameters obtained from the simulation are basically consistent with the experimental literature (Woon Seok Yang, Byung-Wook Park, Eui Hyuk Jung, Nam JoongJeon, Young Chan Kim, Dong Uk Lee, Seong Sik Shin, Jangwon Seo, Eun Kyu Kim, JunHong Noh, Sang Il Seok, Iodide management in formamidinium-lead-halide–based perovskite layers for efficient solar cells, Science 356, 1376–1379 (2017)), and the agreement is very good, which confirms the effectiveness of the simulation parameters in this work. The simulated gradient bandgap CuIn 1-x Ga x Se 2 The schematic diagram of the structure of the perovskite solar cell with a hole transport layer is shown in Figure 2 , and the schematic diagram of the energy band of the gradient bandgap CuIn 1-x Ga x Se 2 is shown in Figure 3 , and the energy band diagram of the contact interface between CuIn 1-x Ga x Se 2 with different Ga contents and the perovskite material is shown in Figure 4 ; the VBO energy band diagram of the contact interface between CuIn 1- x Ga x Se 2 with different Ga contents and the perovskite material is shown in Figure 5 ; the contour map of the conversion efficiency of the perovskite solar cell with a hole transport layer of different gradient bandgap CuIn 1-x Ga x Se 2 is shown in Figure 6 ; the contour map of the conversion efficiency of the perovskite solar cell with a hole transport layer of different gradient bandgap CuIn 1-x Ga xSe 2 The contour map of the open-circuit voltage of the perovskite solar cell with a hole transport layer is shown in Figure 7 ; Different gradient bandgap CuIn 1-x Ga x Se 2 The contour map of the short-circuit current of the perovskite solar cell with a hole transport layer is shown in Figure 8 ; Different gradient bandgap CuIn 1-x Ga x Se 2 The contour map of the fill factor of the perovskite solar cell with a hole transport layer is shown in Figure 9 .

[0036] Figure 2 The schematic diagram of the structure of the perovskite solar cell with a gradient bandgap CuIn 1-x Ga x Se 2 hole transport layer constructed by simulation in Example 1 is given. The cell structure from the bottom layer to the top layer is: metal Au back electrode / CuIn 1-x Ga x Se 2 / CH 3 NH 3 PBI 3 / TiO 2 / FTO / top electrode.

[0037] Figure 3 Shown is the energy band diagram of the perovskite solar cell with a gradient bandgap CuIn 1-x Ga x Se 2 hole transport layer. Eg1 is the bandgap width at the interface in contact with the back electrode Au, and Eg2 is the bandgap width at the interface in contact with the perovskite layer material. The conduction band and valence band are continuously elevated from the interface in contact with the perovskite layer material to the interface in contact with the back electrode Au to form a gradient bandgap.

[0038] Figure 4 Shown is the energy band diagram of the interface between different Ga content CuIn 1-x Ga x Se 2 and the perovskite material. It should be particularly noted that the changes in the conduction band offset CBO and valence band offset VBO at the interface with the change of Ga content. The calculation formulas for the conduction band offset CBO and valence band offset VBO are Formula 4 and Formula 5. The bandgap width and electron affinity of CuIn 1-x Ga x Se 2 in the formula are calculated by Formula 1 and Formula 2 respectively. The variation function of the valence band position with the Ga content is calculated by Formula 3.

[0039] Eg(CuIn 1-x Gax Se 2 ) = (1 - x)Eg(CISe) + x Eg(CGSe) - b x(1 - x) (Equation 1)

[0040] χ(CuIn 1-x Ga x Se 2 ) = (1 - x)χ(CISe) + x χ(CGSe) (Equation 2)

[0041] Ev(CuIn 1-x Ga x Se 2 ) = 0.1x 2 - 0.56x + 5.66 (Equation 3)

[0042] VBO = Eg(CuIn 1-x Ga x Se 2 ) + χ(CuIn 1-x Ga x Se 2 ) - Eg(CH 3 NH 3 PbI 3 ) - χ(CH 3 NH 3 PbI 3 ) (Equation 4)

[0043] CBO = χ(CuIn 1-x Ga x Se 2 ) - χ(CH 3 NH 3 PbI 3 ) (Equation 5)

[0044] From Figure 4 it can be seen that as the Ga content increases (X represents the Ga content), the conduction band and valence band positions of CuIn 1-x Ga x Se 2 gradually rise. The conduction band offset changes from a positive value to a negative value, and the energy band barrier at the interface changes from a peak to a notch. The valence band offset changes from a positive value to a negative value, and the energy band barrier at the interface changes from a peak to a notch. Figure 5 is an enlarged valence band offset diagram.

[0045] Figure 6 For simulating CuIn with different gradient bandgaps 1-x Ga x Se 2Contour map of the conversion efficiency of a perovskite solar cell with a hole transport layer. The abscissa is the doping content of Ga corresponding to Eg1, and the ordinate is the doping content of Ga corresponding to Eg2. When x1 = 0.4 and x2 = 0, the maximum conversion efficiency is 18.32%. When x1 takes a certain value, as x2 increases, the cell efficiency gradually decreases. The reason is that the increase of x2 will increase the conduction band at the interface of the hole layer, making the conduction band offset change from positive to negative, causing the electrons in the hole layer to migrate to the interface, increasing the recombination current, reducing the open-circuit voltage and short-circuit current, and thus reducing the conversion efficiency.

[0046] Figure 7 To simulate CuIn with different gradient bandgaps 1-x Ga x Se 2 Contour map of the open-circuit voltage of a perovskite solar cell with a hole transport layer. It can be found that x1 plays a decisive role in the open-circuit voltage. When the value of x1 is less than 0.2, the open-circuit voltage decreases as x1 decreases. When the value of x1 exceeds 0.2, the open-circuit voltage is not greatly affected by x1, but it slightly decreases as x2 increases. The highest open-circuit voltage is 0.97 eV.

[0047] Figure 8 To simulate CuIn with different gradient bandgaps 1-x Ga x Se 2 Contour map of the short-circuit current of a perovskite solar cell with a hole transport layer. It can be found that x2 plays a major role in the short-circuit current. When x1 takes a certain value, as x2 gradually increases, the short-circuit current gradually decreases. Because the gradual increase of x2 will make the valence band offset peak at the interface too large, hindering the holes in the perovskite layer material from transporting to the hole layer, resulting in a decrease in the short-circuit current. The highest short-circuit current is 23.29 mA / cm 2 .

[0048] Figure 9 To simulate CuIn with different gradient bandgaps 1-x Ga x Se 2 Contour map of the fill factor of a perovskite solar cell with a hole transport layer. When x1 exceeds 0.2, the fill factor gradually decreases as the value of x2 increases. The main reason is that the increase of x2 reduces the short-circuit current, resulting in a decrease in the fill factor. The highest fill factor is 81.29%.

[0049] Example 2

[0050] When CBO = 0.525 eV, VBO = 0.175 eV, the bandgap at the interface in contact with the perovskite = 1.094 eV, and the bandgap at the interface in contact with the back electrode = 1.2 eV, a conversion efficiency of 19.81% much greater than that of a uniform bandgap can be obtained.

[0051] (1) Cu with a gradient bandgap 2 ZnSn(Se 1-x S x ) 4 Hole transport layer, the bandgap at the contact interface between the hole transport layer and the perovskite material is 1.094 eV, and the bandgap at the contact interface between the hole transport layer and the back electrode is 1.2 eV.

[0052] (2) Cu 2 ZnSn(Se 1-x S x ) 4 The bottom of the conduction band and the top of the valence band of the hole transport layer material gradually increase from the contact interface with the perovskite material to the contact interface with the back electrode.

[0053] (3) Cu 2 ZnSn(Se 1-x S x ) 4 The valence band offset VBO at the interface between the hole transport layer and the perovskite material is positive, with a value of 0.175 eV.

[0054] (4) Cu 2 ZnSn(Se 1-x S x ) 4 The conduction band offset CBO at the interface between the hole transport layer and the perovskite material is positive, with a value of 0.525 eV.

[0055] The open-circuit voltage of the perovskite solar cell with the simulated Cu 2 ZnSn(Se 1-x S x ) 4 hole transport layer is 1.05 V, the short-circuit current is 22.94 mA / cm2, the fill factor is 81.95%, and the conversion efficiency is 19.81%. Compared with the existing Cu with a uniform bandgap 2 ZnSn(Se 1-x S x ) 4The highest reported experimental conversion efficiency of hole-transport layer perovskite solar cells is 15.4% (L.S. Khanzada, I. Levchuk, Y. Hou, H. Azimi, A. Osvet, R. Ahmad, et al., Effective ligand engineering of the Cu2ZnSnS4 nanocrystal surface for increasing hole transport efficiency in perovskite solar cells, Adv. Funct. Mater. 26 (2016)). This represents an increase of 4.41%, with a significant improvement of up to 28.6%, indicating a remarkable enhancement effect.

Claims

1. A perovskite solar cell structure with a gradient bandgap hole transport layer, characterized in that: the perovskite solar cell structure has a hole transport layer with a gradient bandgap, and the bandgap width of the contact interface between the hole transport layer and the perovskite material is less than the bandgap width of the contact interface between the hole transport layer and the back electrode; the bottom of the conduction band and the top of the valence band of the hole transport layer gradually increase from the contact interface with the perovskite material to the contact interface with the back electrode; the valence band offset VBO at the interface between the hole transport layer and the perovskite material is positive; the conduction band offset CBO at the interface between the hole transport layer and the perovskite material is positive; the hole transport layer is an inorganic chalcopyrite semiconductor material.

2. The perovskite solar cell structure with a gradient bandgap hole transport layer according to claim 1, characterized in that: the bandgap width of the contact interface between the hole transport layer and the perovskite material is less than the bandgap width of the perovskite material.

3. The perovskite solar cell structure with a gradient bandgap hole transport layer according to claim 1, characterized in that: the bottom of the conduction band of the hole transport layer is lower than that of the perovskite material at the contact interface with the perovskite material, and the top of the valence band of the hole transport layer is lower than that of the perovskite material at the contact interface with the perovskite material.

4. The perovskite solar cell structure with a gradient bandgap hole transport layer according to claim 1, characterized in that: the change range of the valence band offset VBO at the interface between the hole transport layer and the perovskite material is 0.09 eV - 0.3 eV.

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