Enamine‐Based Cross‐Linkable Hole‐Transporting Materials for Perovskite Solar Cells

Abstract

The development of the simple synthesis schemes of organic semiconductors can have an important contribution to the advancement of related technologies. In particular, one of the fields where the high price of the hole‐transporting materials may become an obstacle toward successful commercialization is perovskite solar cells. Herein, enamine‐based materials that are capable of undergoing cross‐linking due to the presence of two vinyl groups are synthesized. It is shown that new compounds can be thermally polymerized, making the films resistant to organic solvents. This can allow the use of a wet‐coating process for the deposition of the perovskite absorber film, without the need for orthogonal solvents. Cross‐linked films are used in perovskite solar cells, and, upon optimization of the film thickness, the highest power conversion efficiency of 18.1% is demonstrated.

A Trifluoroethoxyl Functionalized Spiro‐Based Hole‐Transporting Material for Highly Efficient and Stable Perovskite Solar Cells

“…The current-voltage (J-V) characteristics were measured under 100 mW cm À2 AM1.5G solar illumination. Given that the concentration of Li-TFSI in dopants is one of the important factors in determining photovoltaic performance, we first used 36 μL tBP and Li-TFSI (11,22, and 33 μL) in 1 mL CB as dopants to find the best concentration of Li-TFSI in the PSCs (Figure S9 and Table S3, Supporting Information). Second, we explored the best concentration of Spiro-4TFETAD in the PSCs.…”

Donor–Acceptor Type Polymer Bearing Carbazole Side Chain for Efficient Dopant‐Free Perovskite Solar Cells

“…[ 12,13 ] However, the spiro‐OMeTAD suffers from the low carrier mobility, thus needing to be doped with 4‐ tert ‐butylpyridine ( t ‐BP) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), which increases the overall cost of the device while also compromising its long‐term stability. [ 14–16 ]…”

The Non‐Innocent Role of Hole‐Transporting Materials in Perovskite Solar Cells

“…In the past few years, some examples of this method have appeared in the literature, in which small-molecule HTMs were endowed with crosslinking ability, by conducting tailored modifications of their original structure with the introduction of a polymerizable functional group such as simple ethylene, as shown in Figure 12. [131][132][133][134] The effective crosslinking process can be then activated through different methods. In the first example reported by Hsu and coworkers, a N,N 0 -bis(tolyl)-N,N 0 -bis(vinylphenyl)-1,1 0 -biphenyl-4,4 0 -diamine (DVTPD) HTM was used, that can undergo simple thermally induced crosslinking of the styryl groups at 180 C (Figure 12a), forming a robust film on top of a VO 2 electron blocking layer.…”

“…In another similar case, Getautis and coworkers reported on the use of cost-effective enamine-based cross-linkable HTMs, as the one shown in Figure 12c, in p-i-n PSC configuration, achieving a promising PCE of 18.14%. [133] Here, the crosslinking process was thermally initiated at 231 C, which was identified after conducting an accurate thermal characterization of the newly synthesized HTM through differential scanning calorimetry and thermogravimetric analysis. Tremblay et al designed a photocrosslinkable HTM based on a bis(triarylamine) molecule bearing cinnamate side chains [132] : photocrosslinking is a potentially more advantageous process with respect to thermally induced crosslinking, as it does not require high temperature (>150 C) and thus can be conducted at ambient temperature also on plastic substrates.…”

“…c) Molecular structures of two enamine-based crosslinkable HTMs used in p-i-n devices. Reproduced with permission [133]. Copyright 2020, Wiley-VCH.…”