Phenothiazine-Based Hole-Transporting Materials toward Eco-friendly Perovskite Solar Cells

Abstract

Organic hole-transporting materials (HTMs), AZO-I and AZO-II, were synthesized via Schiff base chemistry by functionalizing a phenothiazine core with triarylamine(s) through azomethine bridges. Substantial enhancements in the power conversion efficiency (PCE = 12.6% and 14% for AZO-I and AZO-II, respectively) and stability (68% or 91% of PCE retained after 60 days for AZO-I or AZO-II, respectively) of perovskite solar cells (PSCs) were achieved when switching from mono-(AZO-I) to disubstituted (AZO-II) HTMs. The extremely low production costs (9 and 12 $/g for AZO-I and AZO-II, respectively), together with the Pd-catalyst-free synthesis, make these materials excellent candidates for lowcost and eco-friendly PSCs.

NIR‐Absorbing Donor–Acceptor Based 1,1,4,4‐Tetracyanobuta‐1,3‐Diene (TCBD)‐ and Cyclohexa‐2,5‐Diene‐1,4‐Ylidene‐Expanded TCBD‐Substituted Ferrocenyl Phenothiazines

“…[13] Furthermore, phenothiazine possesses al ow oxidation potential, whichmakes it auseful electron-donor chromophore in organic photonic materials. [14] In contrast, the cyano-based 1,1,2,2-tetracyanoethylene (TCNE) and 7,7,8,a re known as the most commonly used stronga cceptors. [15] They react with the electron-rich alkynes easily via a[ 2 + +2] cycloaddition-electrocyclic ring-opening reaction.…”

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

“…To ensure the solubility in nonhalogenated solvents while guaranteeing the maximum HTM loading capacity on the perovskite surface and at the same time minimizing the synthesis steps, we modified our previously reported structures ( AZO-I , AZO-II , Scheme 1 ) 37 by (i) making them smaller in size, (ii) introducing an aryl spacer between the phenothiazine and the azomethine bridge ( AZO-III ), and (iii) further adding a thioethyl ( AZO-IV ) group in the 2-position of the phenothiazine unit to enhance the solubility, and possibly also the HTM/perovskite interactions. 2 …”

“…The HOMO level of AZO-III is similar to that of the previously reported AZO-I because it possesses a similar core with the only difference being the position of the electron-donating methoxy-substituted triarylamine units. 37 The HOMO level of Spiro-OMeTAD, as determined by differential pulse voltammetry (DPV) in identical conditions, is −4.82 eV. Because of the small difference between the HOMO levels of AZO-III (0.15 eV) or AZO-IV (0.17 eV) with respect to Spiro-OMeTAD, both new HTMs show high compatibility with the triple-cation halide perovskite (e.g., Cs 0.05 MA 1– y FA y PbI 3– x Cl x ) employed in this work, whose VB lies at −5.9 eV.…”

“… 30 − 32 Recently, they have also been considered as low-cost and effective HTMs for PSCs. 33 − 37 In our previous work, 37 we designed two phenothiazine-core, azomethine-based HTMs ( AZO-I and AZO-II ) via an environmentally friendly Schiff base chemistry approach, starting from low-cost precursors. Even though AZO-I and AZO-II provided a high-performing, stable, and low-cost alternative to Spiro-OMeTAD, their insolubility in nonhalogenated solvents limited their eco-friendliness as regarding their processing in the device fabrication.…”

“…Even though AZO-I and AZO-II provided a high-performing, stable, and low-cost alternative to Spiro-OMeTAD, their insolubility in nonhalogenated solvents limited their eco-friendliness as regarding their processing in the device fabrication. 37 …”