Application of F4TCNQ doped spiro-MeOTAD in high performance solid state dye sensitized solar cells

Abstract

Amid the investigation of solid-state dye-sensitized solar cells (SDSSCs), it was found that the incorporation of F4TCNQ into the solid hole-transporting materials (HTMs) spiro-MeOTAD forms a spiro-MeOTAD/F4TCNQ (strong electron acceptor) polaron charge-transfer complex. Careful examination indicates that the formation of the polaron charge-transfer complex not only facilitates the conductivity of HTMs but also inhibits the charge recombination across the interface of the heterojunction, i.e. photoanode/HTMs and/or counter electrode/HTMs. As a result, the performance of SDSSCs has been markedly improved by using the organic dye A2-F. At AM1.5 illumination the short circuit current densities J(SC) increase from 8.29 mA cm(-2) (w/o F4TCNQ) to 10.95 mA (w/F4TCNQ), accompanied by a 20% increase of the overall power conversion efficiency, η, from 4.55% to 5.44%.

High-Efficient Solid-State Perovskite Solar Cell Without Lithium Salt in the Hole Transport Material

“…Therefore, several kinds of dopants have been developed for spiro-OMeTAD, such as (pBrC 6 38 and F4-TCNQ. 39 However, many of them are usually applied by vacuum deposition or have a poor solubility in organic solvent. 33 Lithium bis(Tri°uoromethanesulfonyl)Imide (LiTFSI) has been found to be a crucial additive for spiro-OMe-TAD to get an increment of conductivity, 40 a better electron injection 41 and retarded recombination.…”

Enhancing the Energy‐Conversion Efficiency of Solid‐State Dye‐Sensitized Solar Cells with a Charge‐Transfer Complex based on 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone

“…The FF improves from 42.6 % for the cell with pristine Spiro‐OMeTAD to 67.1 % for the cell with 0.04 % DDQ added into the HTM. The improvement in the FF is attributed to the fact that the conductivity of the HTM with the 0.04 % doping ratio is higher than that of the pristine reference, which could reduce the hole‐transporting resistance and charge recombination and, thus, lower the series resistance and increase the value of J sc . A slight increase in the doping level to 0.2 % DDQ causes a decrease in the conductivity as a result of a large charge‐transfer resistance of the HTM in the ssDSCs and a decrease in the FF and J sc value.…”

“…There are two semicircles in the diagram; the right arc is obtained from the scan in the low‐frequency range, and it results from charge‐recombination resistance ( R 2 ) between the electrons in the conduction band of TiO 2 and the holes in the HTM. The left arc obtained from the scan in the high‐frequency range is rather complicated, as it results from series resistance ( R 0 ) and charge‐extraction resistance ( R 1 ) at the interface between the HTM and the counter electrode . As shown in the fitted parameter table, the device based on 0.04 % dopant has higher (66.4 vs. 38.7 Ω cm −2 ) charge‐recombination resistance ( R 2 ) than the pristine one, and consequently, if DDQ is added into the device, the rate of electron recombination at the TiO 2 /sensitizer/HTMs interface decreases, so the doped solar cell shows a higher V oc value.…”

“…However, in terms of the structure–properties relationship, as a result of the twisted spiro carbon atom at the center of the Spiro‐OMeTAD structure, intermolecular π–π interactions and those within moieties connected by the spiro center are significantly inhibited, and in consequence, Spiro‐OMeTAD has fairly low hole conductivity . To enhance the conductivity of Spiro‐OMeTAD, numerous additives have been used, including oxygen, SnCl 4 , ( p ‐BrC 6 H 4 ) 3 NSbCl 6 , Co III complexes, protic ionic liquids, lithium bis(trifluoromethanesulfonyl)imide (Li‐TFSI), silver bis(trifluoromethanesulfonyl)imide (Ag‐TFSI), tetrafluorotetracyanoquinodimethane (F4TCNQ), and 1,1,2,2‐tetracholoroethane (TeCA), all of which significantly enhance device performance in ssDSCs. Benzoquinone‐based 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) (Figure S2) as a strong electron acceptor is easily hydrogenated by an electron donor to form a donor–DDQ complex .…”

Effects of polysilane‐doped spiro‐OMeTAD hole transport layers on photovoltaic properties

“…Therefore, judicious selection of light absorber with perovskite structure, organic hole transport layer, and metal contact is indispensable . On the other hand, optimization of amount of polysilanes into spiro‐OMeTAD solution and consideration of compatibility between polysilanes and metal and/or chemical dopants, such as Li, cobalt , silver , N(PhBr) 3 SbCl 6 , and F4TCNQ to increase hole concentration and mobility, are indispensable since doping of excess chemicals and metals into spiro‐OMeTAD solution would leads to degradation of light absorbers and photovoltaic properties , and affects stability of perovskite‐type solar cells.…”