Controlling Vertical Composition Gradients in Sn-Pb Mixed Perovskite Solar Cells via Solvent Engineering

doi:10.15541/jim20220710

Abstract

Abstract:

With a bandgap of 1.1-1.4 eV, Sn/Pb mixed halide perovskites are ideal materials for single-junction solar cells to reach the power conversion efficiencies (PCEs) limit of Shockley-Queisser (S-Q) theory. Their chemical composition gradient in the vertical direction of the perovskite films affect the transport and separation of carriers by changing the energy band structures. Therefore, it is very important to control the crystallization process of tin-lead mixed perovskite thin films. In this work, it was found that different vertical composition gradients were formed when tin-lead mixed perovskites were prepared with different amounts of the anti-solvent. Larger amounts of anti-solvent was contributed to higher lead content on the film surface. The vertical composition gradient of tin-lead mixed perovskite could be regulated by adjusting the solvent composition, among which increasing V(DMSO):V(DMF) in the solvent could form a vertical composition gradient with a lead-rich bottom and a tin-rich surface. When V(DMSO):V(DMF) in lead-based precursor solutions was optimized to 1 : 2, compared with the control group of 1 : 4, open circuit voltage of the device under standard light conditions increased from 0.725 to 0.769 V, short circuit current density from 30.95 to 31.65 mA·cm^-2, and PCE from 16.22% to nearly 18%. Numerical simulations using SCAPS further proved the necessity of forming a vertical composition gradient. When the bottom of the perovskite film is rich in lead and the top is rich in tin, the recombination of carriers in the hole transport layer interface region is reduced, which can improve the device’s performance.

Key words: tin-lead mixed perovskite, solar cell, vertical component gradient, solvent engineering

CLC Number:

TQ174

DAI Xiaodong, ZHANG Luwei, QIAN Yicheng, REN Zhixin, CAO Huanqi, YIN Shougen. Controlling Vertical Composition Gradients in Sn-Pb Mixed Perovskite Solar Cells via Solvent Engineering[J]. Journal of Inorganic Materials, 2023, 38(9): 1089-1096.

Figures/Tables 10

Fig. 1 Crystal structures of perovskite films prepared with different amounts of antisolvent (a) XRD patterns of perovskite films prepared with different amounts of antisolvent; (b) Magnified XRD patterns of (100) lattice plane diffraction peaks; (c) Half-peak width of (100) lattice plane diffraction peaks of thin films at different antisolvent dosages; (d-f) Top-down SEM images of films prepared by 100, 300 and 500 μL antisolvents and statistics of grain sizes

Fig. 2 (a) PL spectra from the front and back sides of PF-DMSO0.25; (b) Cross-sectional SEM images of PSCs of PF-DMSO0.25 and EDS scanning areas; (c) Lead/tin elemental ratios in different depth regions of the cross-sectional SEM images of PF-DMSO0.25 or PF-DMSO0.50; Colorful figures are available on website

Fig. 3 Phase structure and photoelectric properties of perovskites films PF-DMSOx (a) XRD patterns of films and (b) PCE statistics of devices; (c) Time-resolved photoluminescence spectra; (d) Tauc plots of ultraviolet-visible absorption spectra and (e) ultraviolet photoelectron spectra of PF-DMSO0.50 and PF-DMSO0.25; (f) Energy level relationship, (g) J-V curves, (h) external quantum efficiency and integrated current density, (i) Urbach band edge absorption obtained from EQE spectra and fitted electroluminescence spectra of devices fabricated with PF-DMSO0.50 and PF-DMSO0.25; Colorful figures are available on website

Table 1 Main simulation parameters of perovskite solar cell structures

Ingredient	Thickness/μm	E_g/eV	χ/eV	ε_r	N_c/cm^-3	N_v/cm^-3	μ_n/(cm²∙ V^-1∙s^-1)	μ_p/(cm²∙ V^-1∙s^-1)	N_d/cm^-3	N_a/cm^-3	N_t/cm^-3	Ref.
PEDOT: PSS	0.03	2.2	3	3	2.2×10¹⁵	1.8×10¹⁸	0.02	0.0002	-	3.17×10¹⁴	1×10¹⁵	[35,39, 40-42]
Perovskite	0.6	1.25-1.23	4.15-4.2	100	1.0×10¹⁸	1.0×10¹⁸	2	2	-	1.0×10¹⁸	2.5×10¹⁶	[43-45]
PCBM	0.05	2.0	3.9	3.9	2.5×10²¹	2.5×10²⁰	0.2	0.2	2.93×10¹⁷	-	1×10¹⁵	[42, 46]
BCP	0.01	3.5	3.7	10	1.8×10¹⁸	2.2×10¹⁸	0.02	0.002	1×10²¹	1×10¹⁰	1×10	[42, 46]

Fig. 4 Numerical simulation of devices with NG, WO, IG heterojunctions (a) Schematic diagram of the solar cell structures with different vertical composition gradients; (b) Positions of the conduction band, valence band, electron and hole quasi-Fermi levels, (c) electron and hole carrier concentrations, (d) J-V curves and (e) EQE curves; (f) Hole deep-level defect trapping probabilities of normal or inverted gradient devices; Colorful figures are available on website

Fig. S1 XRD pattern of thin films prepared by spin coating SnI2

Fig. S2 (a-d) EDS spectra of regions 1-4 of PF-DMSO0.50 film and (e-h) EDS spectra of regions 1-4 of PF-DMSO0.25 film

Fig. S3 Statistical charts of (a) open-circuit voltage, (b) fill factor and (c) short-circuit current density for devices of PF-DMSOx (x=0.20,0.25,0.33,0.50,1.00)

Fig. S4 UV-Vis absorption spectra of PF-DMSO0.50 and PF-DMSO0.25

Fig. S5 Transmittance spectrum of ITO conductive glass used in the experiments

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