Additive-free, Cost-Effective Hole-Transporting Materials for Perovskite Solar Cells Based on Vinyl Triarylamines

Abstract

A series of cost-effective hole-transporting materials (TOP-HTMs) for perovskite solar cells (PSCs) was designed and synthesized. The molecules, composed of multiple 4,4′-dimethoxytriphenylamines linked to a benzene core via trans-vinylene units, can be manufactured from inexpensive materials through a simple synthetic route. The photophysical, electrochemical, and thermal properties, as well as hole mobilities, were strongly influenced by the position and number of vinyl triarylamine substituents on the core benzene ring. CH3NH3PbI3-based solar cells using the X-shaped TOP-HTM 3 with additives gave a high power conversion efficiency of 17.5% (forward scan)/18.6% (reverse scan). Crucially, TOP-HTMs gave high working device efficiency without the need for conduction-enhancing additives. The power conversion efficiency for the device with additive-free TOP-HTM 3 was 16.0% (forward scan)/16.6% (reverse scan). Device stability is also enhanced and is superior to the reference HTM, 2,2′,7,7′-tetrakis­(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD).

The high open-circuit voltage of perovskite solar cells: a review

“…The authors claimed that chlorine radicals from pentachloroethane transfer partially to spiro-OMeTAD and are retained in the HTM layer, resulting in improved conductivity (comparable to the HTM with dopants). Pentachloroethane has also been used by Nishimura et al 117 for checking the performance of newly synthesized π-conjugated small molecules (TOP-HTM-α1, TOP-HTM-α2, TOP-HTM-α3) without dopants. All these HTMs have a lower HOMO level than spiro-OMeTAD, showing higher V OC than that achieved with the latter, even when they are dopant-free.…”

Advancements in organic small molecule hole-transporting materials for perovskite solar cells: past and future

“…PSCs based on TOP-HTM 3 additive contained high PCE of 17.5% (forward scan)/18.6% (reverse scan), equivalent to that of the PSC comparison unit based on spiro-OMeTAD additive consisting (18.0%/18.4%). 316 Chen et al were synthesized using conventional Suzuki and Buchwald Hartwigcoupling reactions with a triphenylene-core basis, with two new HTMs (TPH-T) used in mixed ion (FAPbI 3 ) 0.85 (MAPbBr 3 ) 0.15 PSCs with superior performance (19.4%) can be attributed to the desirable energy-level distribution, as well as the excellent charge mobility and extraction efficiency. 317 Many metastable cavities are formed by twisted conformations and hydrogen bonds, which can help with hole transport.…”

The evolution of triphenylamine hole transport materials for efficient perovskite solar cells

“…In addition, the device stability achieved when using these X-shaped HTMs is far superior to that of reference devices with spiro-OMeTAD. 179 Azomethine compounds pave the way for the synthesis of highly efficient, environmentally friendly HTMs via palladiumfree synthetic pathways. Following this strategy, three new organic dopant-free molecules with X-shaped structures, D31, D32, and D33, were successfully synthesized and characterized.…”

“…In addition, the device stability achieved when using these X-shaped HTMs is far superior to that of reference devices with spiro-OMeTAD . 179…”