N-Substituted Phenothiazines as Environmentally Friendly Hole-Transporting Materials for Low-Cost and Highly Stable Halide Perovskite Solar Cells

Abstract

Most of the high-performing halide perovskite solar cells (PSCs) leverage toxic chlorinated solvents (e.g., o -dichlorobenzene or chlorobenzene) for the hole-transporting material (HTM) processing and/or antisolvents in the perovskite film fabrication. To minimize the environmental and health-related hazards, it is highly desirable, yet at the same time demanding, to develop HTMs and perovskite deposition processes relying on nonhalogenated solvents. In this work, we designed two small molecules, AZO-III and AZO-IV , and synthesized them via simple and environmentally friendly Schiff base chemistry, by condensation of electron-donating triarylamine and phenothiazine moieties connected through an azomethine bridge. The molecules are implemented as HTMs in PSCs upon processing in a nonchlorinated (toluene) solvent, rendering their synthesis and film preparation eco-friendly. The enhancement in the power conversion efficiency (PCE) was achieved when switching from AZO-III (9.77%) to AZO-IV (11.62%), in which the thioethyl group is introduced in the 2-position of the phenothiazine ring. Additionally, unencapsulated PSCs based on AZO-III displayed excellent stabilities (75% of the initial PCEs is retained after 6 months of air exposure for AZO-III to be compared with a 48% decrease of the initial PCE for Spiro-OMeTAD-based devices). The outstanding stability and the extremely low production cost ( AZO-III = 9.23 $/g and AZO-IV = 9.03 $/g), together with the environmentally friendly synthesis, purification, and processing, make these materials attractive candidates as HTMs for cost-effective, stable, and eco-friendly PSCs.

Electronic structure and interfacial features of triphenylamine- and phenothiazine-based hole transport materials for methylammonium lead iodide perovskite solar cells

“…The TPA moieties feature a non-planar geometry that confers unique hole transport properties, while the PTZ unit has an electron-donating butterfly structure, suitable for several kinds of functionalization, which allows the formation of stable radical cations. [14][15][16][17][18][19][20][21][22][23][24][25][26] HTMs designed from a combination of TPA and PTZ moieties, e.g. PTZ2 reported by Grisorio et al, 26 have shown efficiencies comparable to those obtained with Spiro-OMeTAD.…”

Synthesis and Characterization of New Conjugated Azomethines End-Capped with Amino-thiophene-3,4-dicarboxylic Acid Diethyl Ester

“…The utilization of azomethine denoted as MS-2 with double 4-[N,Ndi(4-methoxyphenyl)amino]phenyl units as HTM in devices with the structure FTO/bl-TiO 2 /mp-TiO 2 /CH 3 NH 3 PbI 3 /MS-2/Au allowed for obtaining a PCE of 6.68% [ 45 ]. Salunke et al [ 46 , 47 ] reported a series of imines with phenothiazine core end-capped with the TPA unit. The fabricated PSCs (ITO/SnO 2 /Cs 0 .…”

Self-Powered and Low-Noise Perovskite Photodetector Enabled by a Novel Dopant-Free Hole-Transport Material with Bottom Passivation for Underwater Blue Light Communications

“…The phenothiazine unit was introduced to form the main chain; this phenothiazinebased polymer possesses considerable electron-donating ability due to its heteroaromatic units. 22,23,26 The triarylamine functional group was attached to the phenothiazine units as side chains, which provided fascinating hole-transport capability. 27,28 We further functionalized the triarylamine group with a methoxy group, adjusting the HOMO energy level of PPZ-TPA to a deeper level and enhancing the ability to attract holes.…”

“…The phenothiazine-based polymers with cost-effective phenothiazine raw material and the versatile reactive sites exhibit striking advantages, which affords the ingress into the commercial production of HTMs due to their facile synthesis strategy . In addition, it has been verified that sulfur-based heterocycles in HTMs could serve as a Lewis base to passivate the surface defects of perovskite films. , Herein, we synthesize a new triarylamine functionalized phenothiazine polymeric HTL, named poly­[4-(10H-phenothiazin-10-yl)- N , N -bis­(4-methoxyphenyl)­aniline] (PPZ-TPA), which has moderate hole mobility and suitable band alignment for efficient hole extraction and transport.…”

“…In addition, it has been verified that sulfur-based heterocycles in HTMs could serve as a Lewis base to passivate the surface defects of perovskite films. , Herein, we synthesize a new triarylamine functionalized phenothiazine polymeric HTL, named poly­[4-(10H-phenothiazin-10-yl)- N , N -bis­(4-methoxyphenyl)­aniline] (PPZ-TPA), which has moderate hole mobility and suitable band alignment for efficient hole extraction and transport. The phenothiazine unit was introduced to form the main chain; this phenothiazine-based polymer possesses considerable electron-donating ability due to its heteroaromatic units. ,, The triarylamine functional group was attached to the phenothiazine units as side chains, which provided fascinating hole-transport capability. , We further functionalized the triarylamine group with a methoxy group, adjusting the HOMO energy level of PPZ-TPA to a deeper level and enhancing the ability to attract holes. , Additionally, the phenothiazine moiety of PPZ-TPA can efficiently passivate undercoordinated Pb 2+ , suppressing nonradiative recombination and yielding a very low dark current density. Consequently, OIHP photodetectors based on PPZ-TPA HTL demonstrate a low dark current density of 1.26 × 10 –7 A cm –2 at a bias of −0.1 V, a low-noise current value of 4.01 × 10 –13 A Hz –1/2 at 70 Hz, and a high specific detectivity of 2.45 × 10 11 cm Hz 1/2 W –1 at 730 nm.…”