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Abstract
In recent years, a new type of two-dimensional semiconductor material graphite phase carbon nitride (g-C3N4) has been used in photocatalysis, perovskite solar cells, and other fields due to its good photoelectric properties. In this article, we report a method to improve the quality of perovskite films by adding boron-doped graphite phase carbon nitride to the perovskite precursor solution. Compared with the perovskite film prepared by adding the precursor solution of graphite phase carbon nitride, the crystal quality of the perovskite film prepared by adding the precursor solution of boron-doped graphite phase carbon nitride has been improved. Perovskite films are characterized by larger grain sizes and tighter arrangements. The power conversion efficiency (PCE) of the prepared perovskite solar cell (PSC) increased from 10.75% to 12.76%.
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1. Introduction
The last decade has seen a growing trend towards organic-inorganic perovskite solar cells, which have attracted the attention of many scientific researchers due to their simple process, low cost, and excellent photoelectric performance. Defect passivation is one of the effective methods to improve the photoelectric performance of perovskite solar cells. The addition of passivation agents is a main means of defect passivation [1].
In recent years, graphitic carbon nitride (g-C3N4) and its derived materials have been used in photo-catalyst and electro-catalyst for heterogeneous catalytic systems, due to its high chemical and thermal stability, tunable bandgap and easy stripping [2–6]. Graphitic carbon nitride has also been reported in the field of perovskite solar cells. Jiang et al. doped g-C3N4 into perovskite thin films, and passivated the perovskite films by controlling the crystallization and reducing the defect density [7]. Chen et al. use a carbonitride-modified SnO2 nanocomposite, SnO2/graphitic carbon nitride (g-C3N4) quantum dots, which was designed as the functional electron transport layer (ETL) to precisely regulate the interfacial charge dynamics for high-performance PSCs [8]. Xie et al. introduced g-C3N4 as an additive into TiO2-based ETL and found that adding g-C3N4 can improve the crystalline quality of the perovskite layers [9]. Jin et al. reported a valid strategy to enhance the photoconversion efficiency (PCE) of PSCs by modifying graphitic carbon nitride (g-C3N4) nanosheets into an electron transport layer interface [10]. Yang et al. found the addition of g-C3N4 into the perovskite precursor solution can improve the crystal quality of perovskite film with good surface morphology and large grain size, and the experiment showed that the best doping concentration was 0.5wt% [11].
Wei et al. calculated the electronic properties, optical and adsorption properties of the original and boron-doped monolayer g-C3N4 on the basis of first-principles density functional theory. According to the study of defect formation energy, it is found that the introduction of boron atoms can reduce the band gap of the original g-C3N4 [12]. Ma et al. used borax, boric acid, and boron oxide as boron sources to dope graphite phase carbon nitride (g-C3N4) with boron. Through a series of experiments, they determined the optimal doping boron source, doping temperature and doping ratio, and optimized the doping treatment method. The incorporation of boron broadens the response range of the sample to visible light, reduces the band width of the sample, improves the utilization of visible light, and at the same time inhibits photo-generated electron-hole recombination, increases the specific surface area, and thus significantly improves the photocatalytic performance of the sample [13].
In this work, we report a method to improve the quality of perovskite films by adding boron-doped graphite phase carbon nitride to the perovskite precursor solution. Compared with the perovskite film prepared by adding the precursor solution of graphite phase carbon nitride, the crystal quality of the perovskite film prepared by adding the precursor solution of boron-doped graphite phase carbon nitride has been improved. The characteristics are The grain size is larger, and the surface is smoother and denser. The PCE of the prepared perovskite solar cell increased from 10.75% to 12.76%.
2. Experimental section
2.1 Materials preparation
PbI2 and methyl-ammonium iodide (MAI) were purchased from Xi’an p-OLED Crop. Dimethylformamide (DMF), dimethyl sulfoxide (DMSO) were purchased from J&K Scientific. FTO, carbon electrode paste, zirconium dioxide paste, and 18NR-T paste were from shanghai MaterWin. The g-C3N4 was purchased from Macklin.
Boron oxide was selected as the boron source, boron atom and g-C3N4 were added to an appropriate amount of ethanol at a molar ratio of 1:6 to oscillate, then heated in an autoclave at 100 °C for 6 h, cooled, dried and ground, calcined at 550 °C for 4 h, and the heating rate was 2 °C / min. After cooling, the product was added to ethanol, washed, dried, and ground to obtain the sample. The sample is boron-doped graphite phase carbon nitride [13]. In this article, the boron-doped graphite phase carbon nitride is labeled ‘B-CN’.
2.2 Fabrication of perovskite solar cells
F-doped tin oxide (FTO) glasses were cleaned by detergent, deionized water, acetone, isopropanol, and ethanol in an ultrasonic bath for 20 min respectively, and UV-ozone treated for 20 min. A compact TiO2 (c-TiO2) layer was deposited on the former prepared FTO glass using the titanium dioxide solution at 4000 rpm for 30 s, then dried the sample at 125°C, repeating the above operation once, and then at 500°C annealing for 30 min. After the above steps, a TiO2 nanoparticle paste (18NRT) thinned in ethanol (1: 5) was spin-coated onto the c-TiO2, then dried the sample at 125°C for 10 min, and the sample was treated at 500 °C for 30 min to form a mesoporous TiO2 (m-TiO2). Followed by, zirconium dioxide paste thinned in ethanol (1: 5) was spin-coated onto the m-TiO2, then dried the sample at 125°C for 10 min, and the samples were treated at 500 °C for 30 min to form a mesoporous ZrO2 (m-ZrO2). The samples were treated with UV-ozone for 20 min. The perovskite precursor solution with 0.5wt% B-CN was dropped onto the m-TiO2 layer and spin-coated in a process of 4000 rpm for 30 s. During this process, 150 µl of toluene as an anti-solvent was dripped down the spinning substrate in 16 s. Then the samples were heated at 100°C for 10 min. At the same time, we need the control group to spin coat with 0.5wt% g-C3N4 doped perovskite precursor solution. Finally, we screen-printed the carbon paste on the perovskite film as the electrode, and then processed the sample on a platform heating plate at 100°C for 30 min. The schematic diagram of the device is shown in Fig. 1(a). A multilayer FTO/c-TiO2/m-TiO2/m-ZrO2/B-CN + perovskite/carbon device was prepared.
Fig. 1. (a) Schematic show of the multilayer device (FTO/c-TiO2/m-TiO2/m-ZrO2/B-CN + perovskite/carbon), (b) Cross-sectional SEM image of the device obtained at ×50 k magnification.
2.3 Characterizations
The crystal structure was measured by XRD (Empyrean).The morphology of perovskite film was measured by the Field Emission Scanning Electron Microscope (JSM-7500F). The optical absorption spectra was recorded on a UV-vis (ultraviolet-visible) spectrophotometer (UV-3600). The J-V (current density-voltage) curves of the perovskite solar cells were measured by an electrochemical work station (IM6).
3. Results and discussion
Figure 2 shows the XRD diffraction pattern of B-CN and the standard card of g-C3N4. We can see that B-CN has obvious characteristic diffraction peaks at 13.1° and 27.8°. The diffraction peak at 27.8° is the characteristic peak of aromatics interlayer accumulation, corresponding to the product having a graphite-like layered structure, and the crystal face index is marked as (002). This is consistent with the previously reported literature [12]. By comparison, we can find that the crystal structure of the doped sample has not changed, and it is still a two-dimensional graphite phase structure.
Figure 3 is the SEM images of the perovskite layer of the samples, and the magnification is ×20k. We can clearly see the surface morphology of the perovskite layer of the sample, and we can find that the B-CN doped perovskite has a larger grain size, and the surface is smoother and denser.
The photovoltaic parameters of perovskite solar cells with different perovskite films are shown in Table 1 and Fig. 4. For pristine perovskite, PSCs exhibit poor performance with a short-circuit current density (Jsc) of 20.27 mA/cm2, open circuit voltage(Voc) of 1.015 V, fill factor (FF) of 52.24, and PCE of 10.75%, respectively. When perovskite is doped with 0.5wt% g-C3N4, PSCs exhibit good performance with a short-circuit current density (Jsc) of 20.47 mA/cm2, open circuit voltage(Voc) of 1.005 V, fill factor (FF) of 56.41, and PCE of 11.61%. When perovskite is doped with 0.5wt% B-CN, PSCs exhibit better performance with a short-circuit current density (Jsc) of 21.85 mA/cm2, open circuit voltage(Voc) of 0.986 V, fill factor (FF) of 59.93, and PCE of 12.76%. Figure 4(b) shows the UV-vis absorption spectra of g-C3N4 and B-CN doped perovskite films. Obviously, the perovskite film containing 0.5 wt% B-CN additive has higher light absorption in the wavelength range of 400-800 nm. Figure 4(c) gives the steady-state photoluminescence (PL) spectra of MAPbI3, MAPbI3 + g-C3N4 and MAPbI3 + B-CN films on FTO substrates. The PL intensity of MAPbI3 + B-CN based sample is obviously weaker than that in MAPbI3 + g-C3N4 and pristine MAPbI3 based samples, indicating an enhanced charge extraction and suppressed carrier recombination. We attribute it to fewer defects due to the stronger passivation effect of B-CN than g-C3N4. The incident photon-to-current conversion efficiency (IPCE) for the differdent devices in a wavelength range of 300–900 nm is characterized in Fig. 4(d). For PSCs decorated with B-CN doped perovskite films, the enhancement of IPCE was investigated, which contributes to higher integrated current density.
Fig. 4. (a) characteristics of PSCs with different perovskite films, (b)UV-vis absorption spectra of perovskite films(c)PL spectra of perovskite films, (d) IPCE spectra and integrated current density of different PSCs.
Table 1. Photovoltaic parameters of perovskite solar cells with different perovskite films.
4. Conclusions
In summary, we have demonstrated a strategy for passivating perovskite crystals by adding boron-doped graphite phase carbon nitride to the perovskite precursor solution. Compared with the perovskite film prepared by adding the precursor solution of graphite phase carbon nitride, the crystal quality of the perovskite film prepared by adding the precursor solution of boron-doped graphite phase carbon nitride has been improved. The characteristics are The grain size is larger, and the surface is smoother and denser. In addition, B-CN can more effectively passivate charge recombination centers around grain boundaries to reduce the intrinsic defect density. Accordingly, the efficiency of the prepared perovskite solar cells increased from 10.75% to 12.76%. This work provides a simple method to improve the crystal quality of perovskite films by controlling crystallization and reducing defect density.
Disclosures
First author Xinwei Jinhua and corresponding author Jinghua Hu and other co-authors have no conflict of interest.
Data availability
Data underlying the results presented in this paper are available in Refs. [11,13].
References
1. F. Gao, Y. Zhao, X. Zhang, and J. You, “Recent progresses on defect passivation toward efficient perovskite solar cells,” Adv. Energy Mater. 10(13), 1902650 (2019). [CrossRef]
2. X. Wang, K. Maeda, A. Thomas, K. Takanabe, G. Xin, J. M. Carlsson, K. Domen, and M. Antonietti, “A metal-free polymeric photocatalyst for hydrogen production from water under visible light,” Nat. Mater. 8(1), 76–80 (2009). [CrossRef]
3. X. F. Wei, J. H. Liu, and X. W. Liu, “Ultrafine dice-like anatase TiO2 for highly efficient dye-sensitized solar cells,” Sol. Energy Mater. Sol. Cells 134, 133–139 (2015). [CrossRef]
4. X. F. Wei, M. M. Zhang, X. Q. Liu, F. Chen, X. Y. Lei, H. Liu, F. C. Meng, H. L. Zeng, S. F. Yang, and J. H. Liu, “Semitransparent CH3NH3PbI3 films achieved by solvent engineering for annealing- and electron transport layer-free planar perovskite solar cells,” Sol. RRL 2(6), 1700222 (2018). [CrossRef]
5. Z. H. Wei, H. N. Chen, K. Y. Yan, and S. H. Yang, “Inkjet printing and instant chemical transformation of a CH3NH3PbI3/nanocarbon electrode and interface for planar perovskite solar cells,” Angew. Chem., Int. Ed. 53(48), 13239–13243 (2014). [CrossRef]
6. T. W. Kim, S. Uchida, T. Matsushita, L. Cojocaru, R. Jono, K. Kimura, D. Matsubara, M. Shirai, K. Ito, H. Matsumoto, T. Konda, and H. Segawa, “Self-organized superlattice and phase coexistence inside thin film organometal halide perovskite,” Adv. Mater. 30(8), 1705230 (2018). [CrossRef]
7. L. L. Jiang, Z. K. Wang, M. Li, C. C. Zhang, Q. Q. Ye, K. H. Hu, D. Z. Lu, P. F. Fang, and L. S. Liao, “Passivated perovskite crystallization via g-C3N4 for high-performance solar cells,” Adv. Funct. Mater. 28(7), 1705875 (2018). [CrossRef]
8. J. B. Chen, H. Dong, L. Zhang, J. R. Li, F. H. Jia, B. Jiao, J. Xu, X. Hou, J. Liu, and Z. X. Wu, “Graphitic carbon nitride doped SnO2 enabling efficient perovskite solar cells with PCEs exceeding 22%,” J. Mater. Chem. A 8(5), 2644–2653 (2020). [CrossRef]
9. F. Y. Xie, G. F. Dong, K. C. Wu, Y. F. Li, M. D. Wei, and S. W. Du, “In situ synthesis of g-C3N4 by glass-assisted annealing route to boost the efficiency of perovskite solar cells,” J. Colloid Interface Sci. 591, 326–333 (2021). [CrossRef]
10. J. R. Jin, S. Z. Wu, X. J. Yang, Y. J. Zhou, Z. H. Li, Q. F. Cao, B. Chi, J. Li, L. Zhao, and S. M. Wang, “Improve the efficiency of perovskite solar cells through the interface modification of g-C3N4 nanosheets,” Mater. Lett. 304, 130685 (2021). [CrossRef]
11. Z. L. Yang, Z. Y. Zhang, W. L. Fan, C. S. Hu, L. Zhang, and J. J. Qi, “High-performance g-C3N4 added carbon-based perovskite solar cells insulated by Al2O3 layer,” Sol. Energy 193, 859–865 (2019). [CrossRef]
12. B. Wei, W. Wang, J. F. Sun, Q. Mei, Z. X. An, H. J. Cao, D. D. Han, J. Xie, J. H. Zhan, and M. X. He, “Insight into the effect of boron doping on electronic structure, photocatalytic and adsorption performance of g-C3N4 by first-principles study,” Appl. Surf. Sci. 511, 145549 (2020). [CrossRef]
13. Y. G. Ma, X. F. Guo, Q. F. Wu, H. B. Wang, Q. Xiang, and B. Chai, “Study on boron-doped graphitic carbon nitride and its photocatalytic property,” New Chemical Materials 47(6), 204–210 (2019).
