Lithium salts as “redox active” p-type dopants for organic semiconductors and their impact in solid-state dye-sensitized solar cells

Abate, Antonio; Leijtens, Tomas; Pathak, Sandeep; Teuscher, Joël; Avolio, Roberto; Errico, Maria Emanuela; Kirkpatrik, James; Ball, James M.; Docampo, Pablo; McPherson, Ian J.; Snaith, Henry J.

doi:10.1039/c2cp44397j

Cited by 586 publications

(720 citation statements)

References 74 publications

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“…However, spiro‐MeOTAD suffers from low hole mobility and conductivity,43 owing to its pristine, unique structure. Additives, such as Li‐bis(trifluoromethanesulfonyl) imide (Li‐TFSI), perfluoro‐tetracyanoquino‐dime thane (F4TCNQ) and tris(2‐(1H‐ pyrazol‐1‐yl) pyridine) cobalt(III) (FK102 Co(III)) are necessary to dope and improve conductivity of spiro‐MeOTAD,43, 44 rendering high‐cost and complex synthesis in corresponding perovskite solar cell fabrication. To mitigate these problems, 2,2′,7,7′‐tetrakis (N,N‐di‐p‐methoxyphenylamine)‐9,9′‐spiro bifluorenedi [bis‐(trifluorom thanesulfonyl) imide] (spiro(TFSI)2; molecular structure is shown in Figure 6) has been studied, which enhances hole conductivity of spiro‐MeOTAD in inert atmosphere instead of oxidation in air.…”

Section: Htmsmentioning

confidence: 99%

High Performance Perovskite Solar Cells

et al. 2015

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Perovskite solar cells fabricated from organometal halide light harvesters have captured significant attention due to their tremendously low device costs as well as unprecedented rapid progress on power conversion efficiency (PCE). A certified PCE of 20.1% was achieved in late 2014 following the first study of long‐term stable all‐solid‐state perovskite solar cell with a PCE of 9.7% in 2012, showing their promising potential towards future cost‐effective and high performance solar cells. Here, notable achievements of primary device configuration involving perovskite layer, hole‐transporting materials (HTMs) and electron‐transporting materials (ETMs) are reviewed. Numerous strategies for enhancing photovoltaic parameters of perovskite solar cells, including morphology and crystallization control of perovskite layer, HTMs design and ETMs modifications are discussed in detail. In addition, perovskite solar cells outside of HTMs and ETMs are mentioned as well, providing guidelines for further simplification of device processing and hence cost reduction.

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Section: Htmsmentioning

confidence: 99%

High Performance Perovskite Solar Cells

et al. 2015

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“…A 70 mM solution of Spiro-MeOTAD (spiro) dissolved in chlorobenzene was used as a hole conductor. To improve the performance of the spiro, three different additives were added 9,10 : 4-tert-butylpyridine, 1.8 M Li-TFSI in acetonitrile, and 0.25 M Co[t-BuPyPz]3[TFSI]3, also known as FK209, in acetonitrile. The Spiro:FK209:Li-TFSI:TBP molar ratio was 1:0.05:0.5:3.3.…”

Section: ~S3~mentioning

confidence: 99%

Unreacted PbI₂ as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

et al. 2016

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Lead halide perovskites have over the past few years attracted considerable interest as photo absorbers in PV applications with record efficiencies now reaching 22%. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3) x (CH(NH2)2)(1–x)PbBr y I(3–y). In this work a broad range of characterization techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV–vis, electroluminescence (EL), photoluminescence (PL), and confocal PL mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices were over 18% efficient, and had in line with previous results a small amount of excess PbI2. For the PbI2-deficient samples, the photocurrent dropped, which could be attributed to accumulation of organic species at the grain boundaries, low charge carrier mobility, and decreased electron injection into the TiO2. The PbI2-deficient compositions did, however, also have advantages. The record V oc was as high as 1.20 V and was found in PbI2-deficient samples. This was correlated with high crystal quality, longer charge carrier lifetimes, and high PL yields and was rationalized as a consequence of the dynamics of the perovskite formation. We further found the ion migration to be obstructed in the PbI2-deficient samples, which decreased the JV hysteresis and increased the photostability. PbI2-deficient synthesis conditions can thus be used to deposit perovskites with excellent crystal quality but with the downside of grain boundaries enriched in organic species, which act as a barrier toward current transport. Exploring ways to tune the synthesis conditions to give the high crystal quality obtained under PbI2-poor condition while maintaining the favorable grain boundary characteristics obtained under PbI2-rich conditions would thus be a strategy toward more efficiency devices.

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“…Ionic compounds such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and 4-tert-butylpyridine (TBP) have been used as additives to spiro-OMeTAD in DSCs. [12][13][14][15] On the other hand, several studies indicate that the conductivity is enhanced by increasing the oxidized species of spiro-OMeTAD (spiro-OMeTAD + ) by doping with Co(III) complexes. [16][17][18][19][20] For example, Grätzel et al reported an improvement in the performance of spiro-OMeTAD-based ssDSCs by using tris[2-(1H-pyrazol-1-yl)pyridine]cobalt(III) tris-(hexafluorophosphate) (FK102) as a chemical dopant.…”

Section: Introductionmentioning

confidence: 99%

Novel Cobalt Complexes as a Dopant for Hole-transporting Material in Perovskite Solar Cells

et al. 2017

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We report herein the synthesis of new cobalt complexes tris [2-(1H-pyrazol-1-yl, which we use as a dopant to create a hole-transporting material in perovskite solar cells. The addition of Co1-Co4 to 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamino)-9,9′-spirobifluorene (spiro-OMeTAD) in chlorobenzene changes the color of the material, which indicates that charge transfer occurs between spiro-OMeTAD and Co1-Co4. Devices made from spiro-OMeTAD doped by Co1, Co2, and Co4 perform better than those made from Co3 because of the presence of hydrophobic alkyl groups on the ligands. An overall power conversion efficiency of 14.8% is obtained by using Co2 as a dopant, which exceeds that of tris[2-(1H-pyrazol-1-yl)-4-tert-butylpyridine]cobalt(III) tris[bis(trifluoromethylsulfonyl)imide] (FK209) under the same conditions with spiro-OMeTAD as a hole-transporting material.

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Lithium salts as “redox active” p-type dopants for organic semiconductors and their impact in solid-state dye-sensitized solar cells

Cited by 586 publications

References 74 publications

High Performance Perovskite Solar Cells

High Performance Perovskite Solar Cells

Unreacted PbI₂ as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

Novel Cobalt Complexes as a Dopant for Hole-transporting Material in Perovskite Solar Cells

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Lithium salts as “redox active” p-type dopants for organic semiconductors and their impact in solid-state dye-sensitized solar cells

Cited by 586 publications

References 74 publications

High Performance Perovskite Solar Cells

High Performance Perovskite Solar Cells

Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

Novel Cobalt Complexes as a Dopant for Hole-transporting Material in Perovskite Solar Cells

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Unreacted PbI₂ as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells