Impact of Alkyl Chain Length on the Properties of Fluorenyl-Based Linear Hole-Transport Materials in p-i-n Perovskites Solar Cells

Abstract

To develop low-cost and highly efficient hole-transport materials (HTMs), a series of linear HTMs based on a fluorenyl core were synthesized with different alkyl side chains substituted for the middle carbon atom, from methyl (FMT-M), and 2-ethylhexyl (FMT-EH) to dodecyl (FMT-D). Together with the hexyl substituent one (FMT), the photophysical and electronic properties, and hole-mobility of the compounds were investigated to determine the influence of the alkyl side chain on the performance of the material as dopant-free HTMs in p-i-n perovskite solar cells (pero-SCs) with the structure of ITO/HTM/MAPbI 3-x Cl x /C 60 /BCP/Ag. All the linear molecules exhibit promising HTM properties including high transmittance, hole-mobility, and optimal energy level alignment with perovskites (MAPbI 3-x Cl x ). As the alkyl chain gets longer, the highest efficiency of corresponding p-i-n pero-SCs based on FMT-M, FMT-EH, FMT, and FMT-D increases from 16.68 and 17.60 to 18.57 and 19.99%, respectively. Through the investigation, it is determined that the alkyl side chain will affect the thermal stability, the melting point, and the intermolecular stacking of the linear molecules; thus, the corresponding HTMs obtain different transparency, hole-transport mobility, energy level, and film morphology, which together will affect the p-i-n pero-SCs performance.

Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All‐Perovskite Tandem Solar Cells with Efficiency over 25%

“…In this work, the effect of the chain length on the efficiency was examined when the monomolecular layer is fabricated on the PTAA. [ 28,29 ] Finally, the target device achieves a PCE of 16.57%. Besides, the all‐perovskite tandem solar cells with the WBG‐Pb‐PSCs and the narrow bandgap Sn/Pb PSCs gave the PCE of 25.24%.…”

Exploration of the Effect of Fluoridation on the Doping-Free Linear Dibenzothiophene-Based Hole-Transport Material Applied for Inverted Perovskite Solar Cells

“…Also, the fractions of τ1 and τ2 for perovskites on ITO, DBT-2F-MOP, and DBT-MOP films are 0.54 versus 0.46, 0.71 versus 0.23, and 0.90 versus 0.10, respectively. The increased fraction of τ1 and the reduced fraction of τ2 for the perovskites on top of the DBT-MOP film illustrate that a well-matched charge collection and transport happened through the interface, which further certifies the increased J SC and FF value of the DBT-MOP-based devices. ,, …”

“…The simulation’s equivalency circuit is shown in the inset in Figure D, and the Nyquist plots were fitted using the sheet resistance ( R s ) and charge-transfer resistance ( R tr ). As the HTL changed from DBT-2F-MOP to DBT-MOP, the R s and R tr values of the corresponding devices decreased from 183.32 to 133.21 and from 11.36 to 9.97 Ω, respectively, which suggests a better ohmic contact between DBT-MOP and the electrode and an enhancement of charge transfer and collection between the DBT-MOP and perovskite. − …”

Structural divergence of molecular hole selective materials for viable p-i-n perovskite photovoltaics: a comprehensive review

“…They utilized them as HSMs along with the hexyl substituted FMT with mixed halide perovskite, MAPbI 3− x Cl x , as a light absorber. 126 The hole carrier mobility was found to be increased on increasing the alkyl chain length from a minimum of 3.78 × 10 −5 cm 2 V −1 s −1 for FMT-M to a maximum of 1.14 × 10 −4 cm 2 V −1 s −1 for FMT-D, although there was no such trend observed with their energy level and thermal stabilities. Furthermore, a smoother surface of FMT-D was achieved with a root-mean-square (RMS) roughness of 0.317 nm that assisted in the formation of a better crystalline perovskite film, as evident from the observed strong intensity of the (110) diffraction peak at a 2 θ of 14.2° and larger perovskite grain size (∼410 nm) from SEM measurements (Fig.…”