Conjugation Engineering of Spiro-Based Hole Transport Materials for Efficient and Stable Perovskite Solar Cells

Abstract

The spiro-type hole transport materials (HTMs) highly depend on the dopants, which increase the hygroscopicity and damage the stability of perovskite solar cells (PSCs). Herein we propose an effective linearization strategy and conjugate engineering modulation to improve the hole mobility and hydrophobicity of spiro-type HTMs. It is found that the spiro-type HTMs with a larger conjugation unit outperforms the short ones with respect to the power conversion efficiency (PCE) and long-term stability, regardless of whether or not the dopants are used. Due to good hole transport and film formation properties, the doped M6-F exhibits high efficiency in both large-area (1.01 cm2, 20.31%) and small-area (0.1 cm2, 22.17%) devices. Moreover, a PSC based on dopant-free M6-F yields an efficiency of 21.21% (stabilized PCE is 20.59%). This work provides a rational and effective way to break the bottleneck of developing spiro-type HTMs.

Recent Progress of Helicene Type Hole-Transporting Materials for Perovskite Solar Cells

“…Thus, it is desirable to develop alternative HTMs with low cost of production and appropriate properties capable of significantly improving the efficiency and stability of devices. Different molecular frameworks with spiro-type core [ 17 , 18 , 19 , 20 , 21 ], D-π-D [ 22 , 23 , 24 , 25 ], D-A-D [ 26 , 27 ], and helicenes [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 ] have been explored to evaluate their applicability as HTMs for n-i-p PSCs.…”

Spiro‐OMeTAD‐Based Hole Transport Layer Engineering toward Stable Perovskite Solar Cells

“…In-depth investigations toward the optimization of Spiro-OMeTAD doping and the fine modulation of the interface properties may further reduce the charge recombination at the interface and lower the charge transport resistance so that the ideal device can have higher V OC and FF. [93,[110][111][112][113][114][115][116][117][118][119][120][121][122][123] At present, the as-prepared HTL film or the precursor solution must be treated with an oxidant such as O 2 to complete the oxidation process, which may introduce extra damage and instability toward PSCs. The content of oxidized Spiro-OMeTAD is important to the device's performance.…”

“…The champion device based on DM delivered a PCE of 23.2% due to a higher V OC than that of the control device using Spiro-OMeTAD as the HTL. Furthermore, the DM-based devices exhibited better thermal stability than those with Spiro-OMeTAD, with 95% of their initial performance maintained after thermal annealing at 60 °C over 500 h, while the control sample degraded rapidly after 50 h. Wu et al [122] combined the rigid structure of fluorinated Spiro-[fluorene-9,9′-xanthene] with a linear configuration to design and synthesize three spiro-type HTLs (labeled as H1-F, H2-F, and M6-F). They demonstrated that the spirotype HTLs with a larger conjugation unit outperformed the short ones in terms of the PCE and long-term stability regardless of whether or not the dopants were used.…”

Broadly Applicable Synthesis of Heteroarylated Dithieno[3,2-b:2′,3′-d]pyrroles for Advanced Organic Materials – Part 2: Hole-Transporting Materials for Perovskite Solar Cells

“…25,26 In another work, a DTP-based HTM bearing a p-methoxyphenyl residue at the DTP nitrogen was synthesized and investigated by Martin, Nazeeruddin et al 27 Very recently, DTP was used in combination with a spiro-type backbone to increase molecular planarity. 28 DTP derivatives are less complex to synthesize than spiro compounds; in this respect, we have recently elaborated and disclosed straightforward direct arylation and heteroarylation procedures to introduce directly π-conjugated aromatic and heteroaromatic substituents at the central DTP-nitrogen. 1,29 Herein, we now describe synthesis and characterization of three novel DTPs, which were functionalized with triarylamine units to result in advanced hole-transport materials (HTM) for perovskite solar cells (PSCs).…”