Recent research progress on optimal design of halide perovskite photovoltaic materials
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摘要: 以CH3NH3PbI3为代表的有机-无机杂化卤化物钙钛矿材料,具有独特优越的光电特性,例如与可见光谱基本匹配的禁带宽度、强的带边光吸收、平衡的双极性载流子输运、超长的载流子扩散距离以及合适的激子结合能等。从2009年到现在,基于钙钛矿材料构建的太阳能电池光电转化效率由最初的不足4%提升到了超过25%,结合低成本的溶液旋涂样品合成方法,使钙钛矿材料成为新型太阳能电池领域的研究热点。然而,高效率钙钛矿材料中铅元素引起的毒性,以及材料本身的不稳定性一直是阻碍太阳能电池及相关光电器件商业化的两大障碍,人们正在努力解决这些问题。在这篇综述中,详细总结了卤化物钙钛矿光伏材料的优化设计,包括结构式为AMX3的单钙钛矿,A2MM'X6的双钙钛矿,A2MX6的有序空位双钙钛矿,A'2An-1MnX3n+1的二维钙钛矿以及类钙钛矿材料(如A3M2X9)。通过材料优化设计,在一定程度上解决或改善了钙钛矿的材料稳定性和毒性问题,但光伏性能仍有待进一步优化提升。在此研究过程中,第一性原理高通量材料模拟在材料设计方面显示了预测能力,得到了与实验研究交互反馈、相互印证的结果。在综述研究进展的同时,进一步讨论了优化设计的新材料存在的问题,并展望了解决这些问题的潜在途径。Abstract: Organic-inorganic halide perovskite, as represented by CH3NH3PbI3, has been attracting increasing attention due to its advanced optoelectronic properties, such as suitable band gaps, high optical absorption, bipolar carrier conductivity, ultralong carrier diffusion length and appropriate exciton binding energy. At present, solar cells based on organic-inorganic halide perovskite have gained enormous significance and reached a power conversion efficiency exceeding 25%, which was less than 4% in 2009. In addition, combined with the low-cost solution spin-coating method for sample preparation, perovskite materials have become the focus of research in the field of novel solar cells. Researchers have been addressing the key challenges facing lead halide perovskites, including their stability and toxicity issues. In this paper, research progress on the optimal designs of halide perovskite photovoltaic materials is reviewed in detail, including single(AMX3), double(A2MM'X6), ordered-vacancy double(A2MX6), 2D(A'2An-1MnX3n+1) perovskites and perovskite-like(A3M2X9) materials. Through rational design, the material stability and toxicity of perovskites have been solved or improved to some extent but the photovoltaic performance has yet to be further optimized. In this research, the first-principles of high-throughput material simulation showed predictive ability in material design. The results of interactive feedback and mutual verification with experimental research were obtained. In addition, the problems introduced by new materials in rational designs are discussed and a powerful method for addressing these problems is proposed.
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Key words:
- solar cell /
- halide perovskites /
- optoelectronic conversion /
- materials by design
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图 2 (a) MAPbI3立方相的晶体结构;(b)MAPbI3的能带结构(纵坐标每小格为0.2 eV)和态密度,从上到下分别为总的态密度,CH3NH3+,Pb,I的分波态密度[50];(c)MAPbI3的价带和导带的部分电荷密度[50];(d)理论计算的MAPbI3,CsSnI3,CsPbI3的光吸收系数[24];(e)MAPbI3与几种常见光伏材料的光电转换效率随层厚度的关系的比较[24]
Figure 2. (a)Crystal structure of MAPbX3 perovskites(MA=methylammonium; X=I, Br, or Cl). (b)The band structure (0.2 eV per division of CH3NH3PbI3 and total DOS and CH3NH3+, Pb, I partial DOS, respectively[50]. (c)The partial charge densities at conduction band minimum(CBM) and valence band maximum(VBM) [50]. (d)The optical absorptions of MAPbI3, CsSnI3 and GaAs[24]. (e)Calculated maximum efficiencies of halide perovskites, CIS, CZTS, and GaAs as a function of film thickness[24]
图 3 (a) MAPbI3的缺陷形成能示意图[50]。(b)中性MAPbI3中点缺陷的跃迁能级,红色和蓝色分别代表受主和施主,括号里表示的是从小到大排序的缺陷形成能。MA+表示CH3NH3+[50]
Figure 3. (a)The formation energies of intrinsic point defects in CH3NH3PbI3[50]. (b)Calculated transition energy levels of point defects in CH3NH3PbI3[50].The formation energies of neutral defects are shown in parenthesis. The red and blue lines represent the acceptors and donors, respectively[50]
图 4 (a) 面积仅为0.095cm2太阳能电池材料的正向和反向扫描的电流-电压(J-V)曲线[62]。(b)80个太阳能电池器件功率转化效率的直方图[62]。(c)面积为1.0 cm2的电流-电压曲线(J-V)[62]
Figure 4. (a)J-V curves of a small PSC(0.095 cm2) in forward- and reverse-scan modes and the corresponding photovoltaic parameters[62]. (b)Histogram of the average power conversion efficiency determined for 80 PSC devices[62]. (c)J-V curve for a large PSC(1.0 cm2) plotted as the average of the reverse- and forward-scan modes and the corresponding photovoltaic parameters[62]
图 6 (a) 计算所得到的FA1-xCsxPbI3合金不同Cs比率α相和δ相的能量差随容差因子t的变化[25]。(b)FAPb(I1-xBrx)3和FA0.83Cs0.17(I1-xBrx)3的不同组分的光吸收系数[77]
Figure 6. (a)Calculated energy difference between α-phase and different δ-phases for FA1-xCsxPbI3alloys with different Cs ratios[25]. (b)UV-vis absorption spectra of FAPb(I1-xBrx)3 and FA0.83Cs0.17Pb(I1-xBrx)3 thin films(FA=formamidinium)[77]
图 7 (a) 由单钙钛矿演化成双钙钛矿的过程[113]。(b)Cs2InBiCl6能带结构和轨道投影态密度[113]。(c)理论计算的A2M+M3+X6Ⅶ钙钛矿最佳光谱[113]。(d)Cs2[AgIn]Cl6的能带投影和跃迁矩阵元[126]
Figure 7. (a)Space of candidate A2M+M3+X6Ⅶ perovskites for materials screening: left panel shows adopted double-perovskite structure, and right panel shows schematic idea of atomic transmutation[113]. (b)Electronic band structures and orbital-projected density of states for Cs2InBiCl6[113]. (c)Calculated absorption spectra of selected optimal A2M+M3+X6Ⅶ perovskites[113]. (d)Band structure and transition matrix elements for Cs2AgInCl6[126]
图 9 (a) Cs2SnI6的晶体结构[136];(b)Heyd-Scuseria-Ernzerhof(HSE)泛函计算的Cs2SnI6的能带结构[137];(c)理论计算的CsSnI3(上)和Cs2SnI6(下)的投影态密度[136];(d)CsSnI3(左)和Cs2SnI6(右)的简易能级示意图[136];(e)Cs2SnI6的固态染料敏化太阳能电池的以一定间隔时间测量的长期的光伏参数[138];(f)Cs2PdBr6的电子能带结构和投影态密度。黑点(1)和(2)表示X点的最高和第二高占据态;(3)表示X点最低未占据态[140]
Figure 9. (a)Crystal structure of Cs2SnI6, which is obtained by removing a half of the Sn atoms at intervals[136]. (b)Band structure of Cs2SnI6 calculated with HSE06[137]. (c)Total and projected densities of states(DOSs/PDOSs) of CsSnI3(top panel), and Cs2SnI6(bottom panel)[136]. (d)Simplified energy diagrams depicting the formation of VBM, CBM, and donor-/acceptor-like defects in (left)CsSnI3 and (right)Cs2SnI6[136]. (e) Long-term measurement of the parameters taken at regular intervals as a function of time[138]. (f)Electronic band structure of Cs2PdBr6[140]
图 10 (a)(PEA)2(MA)n-1PbnI3n+1从二维(n=1)到三维(n=∞)的晶体结构变化[115]。(b)(PEA)2(MA)n-1PbnI3n+1二维钙钛矿和三维钙钛矿的稳定性和效率的比较[115]
Figure 10. (a)Unit cell structure of (C8H9NH3)2(CH3NH3)n-1PbnI3n+1 perovskites with different n values, showing the evolution of dimensionality from 2D(n=1) to 3D(n=∞)[115]. (b)Device performance as a function of n value, which shows that increased performance was achieved with increased n value; however, in the meantime, stability was decreased[115]
图 11 (a) 不同层(PEA)2(MA)Pbn-1I3n+1薄膜结构低角度衍射的XRD图[115]。(b)不同层(PEA)2(MA)n-1PbI3n+1薄膜的光吸收谱[115]。(c)不同层(PEA)2(MA)n-1PbnI3n+1薄膜的电流-电压曲线(J-V)[115]。(d)通过DFT+SOC方法计算的(PEA)2(MA)n-1I3n+1(n=1, 2, 3, 4)的能带结构和MAPbI3是否考虑SOC计算的能带结构的比较[150]
Figure 11. (a)Low-diffraction-angle region of XRD spectra[115].(b)Absorption spectra of the perovskite films with different n values[115]. (c)J-V curve for champion perovskite device with different n values[115]. (d)Calculated band structures of (PEA)2PbI4(N=1-4) by DFT-PBE+SOC, and those of MAPbI3 by DFT with and without SOC[150]
图 12 (a) n=3准二维钙钛矿薄膜中载流子转移的示意图[151]。(b)高度定向二维Sn基钙钛矿薄膜示意图[153]。(c)高度定向(PEA)2(FA)8Sn9I28的最高性能器件的电流密度-电压(J-V)特性。插图显示设备在手套箱中存储超过100小时的标准化的太阳能转换效率[153]
Figure 12. (a)Schematic of carrier transfer in the n=3 perovskite film. The electron transfers from small-n to large-n perovskite phases, and the hole transfers from large-n to small-n perovskite phases[151]. (b)Schematic illustration of the (101) plane of a (PEA)2(FA)8Sn9I28(n=9) 2D perovskite crystal[153]. (c)Current-density voltage(J-V) characteristics of the highest-performance device based on highly oriented (PEA)2(FA)8Sn9I28. The inset indicates the normalized PCE of the device stored in a glove box for over 100 h[153]
图 13 (a) Cs3Sb3I9去除Sb后得到Cs3Sb2I9为代表的层状相的结构[155]。(b)Cs3Sb2I9为代表的二聚体相的结构[155]。(c)HSE计算的层状相和二聚体相的能带结构[155]。(d)层状相和二聚体相的态密度[155]。(e)用于确定层状相Cs3Sb2I9的带隙的光学吸收(插图表示薄膜样品)[155]。(f)理论计算的Cs3Sb2I9层状相和二聚体相的吸收系数和MAPbI3的比较[155]
Figure 13. (a)Removal of every third Sb layer along the <111> direction of the perovskite structure results in the 2D layered modification of Cs3Sb2I9[155]. (b)2D layered modification of Cs3Sb2I9[155]. (c)HSE calculated band structures of Cs3Sb2I9 in layered and dimer modifications[155]. (d)Partial density of states(PDOS) plots of the layered and dimer modifications of Cs3Sb2I9[155]. (e)Band gap of the layered modification of Cs3Sb2I9(inset shows a thin film) was calculated to be 2.05 eV from absorbance data using the Tauc relation[155]. (f)Calculated absorption coefficients for Cs3Sb2I9 with the layered and dimer structures as compared to that of CH3NH3PbI3[155]
表 1 不同类型卤化物双钙钛矿的总结[39]
Table 1. Summary of different categories of halide double perovskites
A2B(Ⅰ)B(Ⅲ)X6 Optoelectronic properties Synthesized compounds (Potential)Applications Type Ⅰ: direct bandgap (MA)2TlBiBr6 (solar cell) s2+s2 suitable bandgap values (light-emission device) strong light absorption high electronic dimensionality expected defect tolerance Type Ⅱ: indirect bandgap Cs2AgBiCl6 solar cell s0+s2 large bandgap values Cs2AgBiBr6 X-ray detector reduced electronic (MA)2AgBiBr6 photocatalysis dimensionality (MA)2AgBiI6 (X-ray imaging) long carrier lifetime Cs2AgSbCl6 not good carrier transport (MA)2AgSbI6 (MA)2KBiCl6 Cs2NaBiCl6 Type Ⅲ: direct bandgap Cs2AgInCl6 photodetector s0+s0 dipole-forbidden transition (MA)2KGdCl6 laser large bandgap values (MA)2KYCl6 light-emission reduced electronic Cs2NaGaF6 device dimensionality Vacancy-ordered direct bandgap Cs2SnI6 solar cell strong light absorption Cs2PdBr6 light-emission existence of deep mid-gap Cs2Ti[Br/I]6 device detects Cs2TeI6 (X-ray imaging) not good carrier transport -
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