染料敏化太阳能电池中额外给体引入对经典D-π-A型敏化剂性能影响的理论研究

doi:10.7503/cjcu20150214

摘要/Abstract

摘要：

为了探讨D-D-π-A型染料中双给体对敏化剂性能的影响, 本文结合密度泛函理论(DFT)及含时密度泛函理论(TD-DFT)对染料1~4的几何结构、电子结构、吸收光谱、电化学性质、电子复合程度以及半导体导带边缘的移动等进行了对比研究. 结果表明, 相比于经典的D-π-A型染料分子1, 在分子2~4(D-D-π-A型双给体染料) 中额外引入给体, 尽管对导带能级移动的改变不是很显著, 但是可以改变体系的共轭程度, 增加染料的光吸收强度. 重要的是, 额外给体的引入可以显著增加染料阳离子空穴-半导体之间的距离, 从而减缓注入电子与染料阳离子的复合; 在额外给体中引入杂原子可以使I₂聚集在染料外侧, 从而降低电解质在半导体表面的局域浓度, 进而减缓注入电子与电解质之间的复合速率. 因此, 通过在经典的D-π-A型染料上引入额外的电子给体构筑D-D-π-A型染料可以有效调节染料的光吸收、电化学及电子复合等方面的性质, 是设计合成高性能染料的可行策略.

关键词: 染料敏化太阳能电池, D-D-π-A型染料, 密度泛函理论, 电子复合, 给体

Abstract:

In order to explore the effect of extra donor on the performance of sensitizer in dye-sensitized solar cell(DSSC), we have analysized geometrical and electronic structures, absorption spectra, electrochemical properties, charge recombination and conduction band shift for four dyes based on density functional theory(DFT) and time-dependent density functional theory(TD-DFT) calculations. The results show that compared with the classical D-π-A sensitizer 1, although the introduction of extra donor has no significant effect on the conduction band shift, it could change the degree of molecular conjugation and increase their molar absorption coefficients. Importantly, the introduction of extra donors could increase significantly the dye cation hole-conduction surface distance, and thus reduce the charge recombination between the injected electron and dye cation. The introduction of extra donors also make I₂ locate at the outside of sensitizer, thus lower the recombination rate between the injected electron and electrolyte. We hope our calculations could provide a clear strategy for experimental synthesis of high performance dyes.

Key words: Dye-sensitized solar cell, D-D-π-A dye, Density functional theory, Charge recombination, Donor

中图分类号:

O641

TrendMD:

吴水星, 张建钊, 苏欣, 张吉, 吴勇, 耿允, 苏忠民. 染料敏化太阳能电池中额外给体引入对经典D-π-A型敏化剂性能影响的理论研究. 高等学校化学学报, 2015, 36(10): 2002.

WU Shuixing, ZHANG Jianzhao, SU Xin, ZHANG Ji, WU Yong, GENG Yun, SU Zhongmin. Theoretical Investigation on the Effect of Extra Donor on the Performance of D-π-A Sensitizer in Dye-sensitized Solar Cell^†. Chem. J. Chinese Universities, 2015, 36(10): 2002.

图/表 9

Fig.1 Molecular structures of isolated organic dyes 1—4

Table 1 Effects of the functionals used on the lowest vertical excitation energy(λ) of dye 2 with the 6-31G* basis set in acetonitrile solution

Functional	λ/eV	Functional	λ/eV
B3LYP	1.90	MPW1K	2.53
BHandHLYP	2.67	CAM-B3LYP	2.70
PBE0	2.05	wB97X	3.01
M06HF	3.14	LC-BLYP	3.13
MPWPW91	1.37	Expt.	3.05

Table 2 Main bond lengths, bond length alternations(BLA) and dihedral angels for dyes 1—4

Dye	Bond length/nm					BLA/nm	∠C1—C2—C3—S/(°)
Dye	C2—C3			C3—C4	C4—C5	C5—C6	C6—C7
1	0.1458	0.1390	0.1403	0.1393	0.1424	0.0037	20.42
2	0.1455	0.1392	0.1401	0.1394	0.1422	0.0033	19.09
3	0.1460	0.1389	0.1404	0.1392	0.1425	0.0039	21.28
4	0.1457	0.1391	0.1402	0.1393	0.1423	0.0035	19.10

Fig.2 Distribution of frontier molecular orbitals for dyes 1—4

Table 3 Calculated maximum absorption wavelength(λmax), oscillator strength(f), light harvesting efficiency(LHE) and transition nature corresponding to S0→S1 for dyes 1—4

Dye	State	Main configuration	λ_max/nm(eV)	f	LHE
1	S₀ → S₁	HOMO-1→LUMO(26%), HOMO→LUMO(65%)	396(3.14)	1.33	0.953
2	S₀ → S₁	HOMO-2→LUMO(30%), HOMO→LUMO(53%)	412(3.01)	1.49	0.967
3	S₀ → S₁	HOMO-5→LUMO(19%), HOMO-2→LUMO(25%), HOMO→LUMO(47%)	390(3.18)	1.43	0.962
4	S₀ → S₁	HOMO-2→LUMO(38%), HOMO→LUMO(41%)	407(3.05)	1.47	0.966

Table 4 Oxidation potential of ground and excited state and corresponding deducing injection and regeneration driving force for dyes 1—4

Dye	E_dye/eV	λ_max/eV	$E dye *$ /eV	ΔG_inj/eV	ΔG_reg/eV
1	-6.39	3.14	-3.25	0.75	1.55
2	-5.64	3.01	-2.63	1.37	0.80
3	-6.12	3.18	-2.94	1.06	1.28
4	-5.63	3.05	-2.58	1.42	0.79

Table 4 Oxidation potential of ground and excited state and corresponding deducing injection and regeneration driving force for dyes 1—4

Dye	E_dye/eV	λ_max/eV	$E dye *$ /eV	ΔG_inj/eV	ΔG_reg/eV
1	-6.39	3.14	-3.25	0.75	1.55
2	-5.64	3.01	-2.63	1.37	0.80
3	-6.12	3.18	-2.94	1.06	1.28
4	-5.63	3.05	-2.58	1.42	0.79

Table 5 Conduction band energy level shift(ΔCB), hole-surface distance(r) and interaction energy of dye-I2 interaction site(Eint) for dyes 1—4

Dye	ΔCB/eV	r/nm	E_int/(kJ·mol^-1)
1	0.2614	1.127	-35.61(1-CN-I₂), -20.63(1-S-I₂)
2	0.2724	1.423	-41.51(2-CN-I₂), -21.71(2-S-I₂)
3	0.2557	1.460	-46.86(3-CN-I₂), -20.17(3-S-I₂)
4	0.2664	1.469	-42.26(4-CN-I₂), -20.84(4-S-I₂)

Fig.3 Optimized molecular structures of dye-I2 complexes and corresponding interaction energies(kJ/mol) for dyes 1—4

Fig.4 Optimized molecular structures of dye-I2 complexes and corresponding interaction energy(kJ/mol) for dye 2

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