4‐Tert‐butylpyridine Free Organic Hole Transporting Materials for Stable and Efficient Planar Perovskite Solar Cells

Abstract

4‐Tert‐butylpyridine (tBP) is an important additive in triarylamine‐based organic hole‐transporting materials (HTMs) for improving the efficiency and steady‐state performance of perovskite solar cells (PVSCs). However, the low boiling point of tBP (196 °C) significantly affects the long‐term stability and device performance of PVSCs. Herein, the design and synthesis of a series of covalently linked Spiro[fluorene‐9,9′‐xanthene] (SFX)‐based organic HTMs and pyridine derivatives to realize efficient and stable planar PVSCs are reported. One of the tailored HTMs, N2,N2,N7,N7‐tetrakis(4‐methoxyphenyl)‐3′,6′‐bis(pyridin‐4‐ylmethoxy) spiro[fluorene‐9,9′‐xanthene]‐2,7‐diamine (XPP) with two para‐position substituted pyridines that immobilized on the SFX core unit shows a high power conversion efficiency (PCE) of 17.2% in planar CH3NH3PbI3‐based PVSCs under 100 mW cm−2 AM 1.5G solar illumination, which is much higher than the efficiency of 5.5% that using the well‐known 2,2′,7,7′‐tetrakis‐(N,N‐di‐p‐methoxy‐phenyl‐amine)9,9′‐spirobifluorene (Spiro‐OMeTAD) as HTM (without tBP) under the same condition. Most importantly, the pyridine‐functionalized HTM‐based PVSCs without tBP as additive show much better long‐term stability than that of the state‐of‐the‐art HTM Spiro‐OMeTAD‐based solar cells that containing tBP as additive. This is the first case that the tBP‐free HTMs are demonstrated in PVSCs with high PCEs and good stability. It paves the way to develop highly efficient and stable tBP‐free HTMs for PVSCs toward commercial applications.

Positional Effect of the Triphenylamine Group on the Optical and Charge‐Transfer Properties of Thiophene‐Based Hole‐Transporting Materials

“…proposed that the donor‐π‐donor planar structure could be strategically important to design small‐molecule HTMs on account of improving charge transfer property and efficient charge extraction properties at the interface between perovskite and HTM . The results from Jen and co‐workers exhibited that pyridine‐functionalized HTM has a vital role in increasing the stability of PSCs . Just recently, our group further studied the variation tendencies of energy level and hole transport property with the change of position and number of methoxy groups for spiro‐CPDT.…”

“…[7] The resultsf rom Jen and coworkers exhibited that pyridine-functionalized HTM has av ital role in increasing the stability of PSCs. [8] Just recently,o ur group further studied the variation tendencies of energy level and hole transport property with the change of position and number of methoxy groups fors piro-CPDT.R esults showed that meta-substitution benefits reducing of the highest occupied molecular orbital( HOMO) levels, and ortho-substitutiono r mixed ortho-and para-substitution could increaset he hole mobility. [9] We also investigated the influence of conjugate unit length on energy level and hole mobility,a nd we found that when the number of conjugate thiophtheneu nit is more than 4, the HOMO level is ac onstant,a nd molecule size ando dd or even number of thiophtheneu nit co-influence the hole transfer property.…”

Introduction of Fluorine Into spiro[fluorene‐9,9′‐xanthene]‐Based Hole Transport Material to Obtain Sensitive‐Dopant‐Free, High Efficient and Stable Perovskite Solar Cells

“…First, the key fluorine containing core moiety 2,7‐dibromo‐3′,6′‐difluoro‐spiro(fluorene‐9,9′‐xanthene) (2Br2F‐SFX) was prepared via one‐pot cyclization reaction of the commercial available 2,7‐dibromo‐9‐fluorenone and 3‐fluorophenol using methanesulfonic acid as catalyst . Subsequently, Buchwald‐Hartwig amination of the 2Br2F‐SFX and 4,4′‐dimethoxydiphenylamine in the presence of palladium‐catalysts afforded the target compound 2 m F‐X59 . The detailed synthetic information and full chemical characterization of the intermediate and target product were fully accessible in the Supporting Information.…”

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

“…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 ) . XPP was designed with two para ‐substituted pyridines on the SFX core unit to perform the role of a tBP without the liquid‐type tBP as a dopant.…”