Tailor-Making Low-Cost Spiro[fluorene-9,9′-xanthene]-Based 3D Oligomers for Perovskite Solar Cells

Abstract

Two low-cost spiro[fluorene-9,9 0 -xanthene] (SFX)-based 3D organic hole transport materials (HTMs), termed X54 and X55, were tailor-made by a one-pot synthesis approach for perovskite solar cells (PSCs). PSC devices based on X55 as the HTM show a very impressive power-conversion efficiency of 20.8% under 100 mW$cm À2 AM1.5G solar illumination, which is much higher than the PCE of the reference devices based on X54 (13.6%) and the standard HTM-Spiro-OMeTAD (18.8%) under the same conditions. HIGHLIGHTS Two SFX-based 3D oligomers were tailor-made by a one-pot synthesis approachOne of the oligomers, X55, was successfully applied in highly efficient PSCs High efficiency of 20.8% was achieved with X55 as the hole transport material The low-cost 3D HTMs can render a PCE close to 21% in PSCs Xu et al., Chem 2, 676-687 May 11, 2017 ª 2017 Elsevier Inc. http://dx. SUMMARYThe power-conversion efficiencies (PCEs) of perovskite solar cells (PSCs) have increased rapidly from about 4% to 22% during the past few years. One of the major challenges for further improvement of the efficiency of PSCs is the lack of sufficiently good hole transport materials (HTMs) to efficiently scavenge the photogenerated holes and aid the transport of the holes to the counter-electrode in the PSCs. In this study, we tailor-made two low-cost spiro[fluorene-9,9 0xanthene] (SFX)-based 3D oligomers, termed X54 and X55, by using a one-pot synthesis approach for PSCs. One of the HTMs, X55, gives a much deeper HOMO level and a higher hole mobility and conductivity than the state-of-theart HTM, Spiro-OMeTAD. PSC devices based on X55 as the HTM show a very impressive PCE of 20.8% under 100 mW$cm À2 AM1.5G solar illumination, which is much higher than the PCE of the reference devices based on Spiro-OMeTAD (18.8%) and X54 (13.6%) under the same conditions.

Rational Design of Cyclopenta[2,1‐b;3,4‐b′]dithiophene‐bridged Hole Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells

“…In this respect, it is important to develop cost‐effective HTMs for further improving PCE. Recently, various types of HTMs based on small organic molecules, polymers and inorganic salts have been reported . However, small‐molecule‐based HTMs are considered to be more valuable over polymer materials because of their facile purification, high purity and smaller batch‐to‐batch variations in the molecular weights.…”

Facilely Synthesized spiro[fluorene‐9,9′‐phenanthren‐10′‐one] in Donor–Acceptor–Donor Hole‐Transporting Materials for Perovskite Solar Cells

“…[1] PSCs have since achieved rapid increase in PCE from 3.8 %t oo ver 20 %, [2][3][4][5][6] owing to the perovskite active layer,w hich exhibits severalb enefits like broad absorptivity, long electron-hole diffusion length, [7] efficient charge-transport capability, [8][9][10] and low charge-recombination rate. In particular,s olar energy has been recognized as a potentiala lternative energy resource.…”

“…[1] PSCs have since achieved rapid increase in PCE from 3.8 %t oo ver 20 %, [2][3][4][5][6] owing to the perovskite active layer,w hich exhibits severalb enefits like broad absorptivity, long electron-hole diffusion length, [7] efficient charge-transport capability, [8][9][10] and low charge-recombination rate. [44,45] Considerable efforts have also been devoted to investigating suitable HTMs by replacing the spiro-based core with novel spiro-based HTMs like spiro-acridine-fluorene, [46,47] spiro-bi[thieno [3,4-b] [1,4]dioxepine], [48] dispiro-oxepine, [49] spiro[fluorene-9,9'-xanthene], [6,[50][51][52][53] and spiro-phenylpyrazole-fluorine. [2,3,5] As Spiro-OMeTAD exhibits al ow recombination rate and efficient hole-transport mobility,t he overall devicep erformance is improved when the materiali si ncluded.…”

Hole Transport Materials in Conventional Structural (n–i–p) Perovskite Solar Cells: From Past to the Future

“…The structure in which two TPAs are connected to fluorene ( X59 ) and four TPAs are connected to SFX ( X60 ) also exhibited 19.8% of efficiency in Per‐SC . The SFX‐terminated X59 , which is called X55 , achieved a high efficiency of 20.8% with high T g (174.4 °C) and hole mobility (6.81 × 10 −4 cm 2 V −1 s −1 ) (Figure ) . A tBP‐free HTM, called XPP , was developed to achieve 19.5% of efficiency in the PerSC (Figures d and ) .…”