Molecular Engineering of Polymeric Hole-Transporting Materials for Efficient and Stable Perovskite Solar Cells

Abstract

Perovskite solar cells (PSCs) have achieved boosted efficiency growth in the last decade by utilizing 2,2′,7,7′-tetrakis­(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD). Various dopant-free small molecules and polymers were introduced as hole-transporting materials (HTMs) to revamp the drawbacks of spiro-OMeTAD such as poor stability, high cost, and sophisticated processing. Herein, a polymer showing enhanced π-conjugation, trithiophene-benzene (TTB), was put forward through molecular engineering by further modifying the previously reported HTM [2,4-dithiobiuret (DTB)]. One more thiophene was embedded into the main chain to increase the exposure of sulfur atoms to perovskite, as well as to enhance the conjugation effect. The continuously maintained π–π stacking guarantees smooth hole extraction from the perovskite layer. TTB-based PSCs not only show a high power conversion efficiency (PCE) of 18.2% in high-level devices with dopant-free organic HTMs but also demonstrate outstanding ambient stability, retaining 91.1% of their initial PCE after 30 days of storage.

Triphenylamine (TPA)‐Functionalized Structural Isomeric Polythiophenes as Dopant Free Hole‐Transporting Materials for Tin Perovskite Solar Cells

“…Note, the sulfur atom in the SBT unit of polymers can also act as a Lewis base to passivate perovskite surface defects and enhance the stability of TPSCs. [54] The wettability and crystal morphology of the tin perovskites deposited on these polymeric HTMs are shown in Figure 4. We first made the HTM films on ITO substrate via spin-coating, then the hydrophobic surfaces of HTMs were modified by the anilinium iodide (ANI) [41] species to make the film surfaces becoming hydrophilic to some extent.…”

Underlying Interface Defect Passivation and Charge Transfer Enhancement via Sulfonated Hole-Transporting Materials for Efficient Inverted Perovskite Solar Cells

“…Most of the reported polymeric HTMs struggle to be truly cost-effective due to the usage of noble metal catalysts during a synthetic process. − Remarkably, the newly developed polymeric HTMs can be obtained by a cheap synthetic route via the Wittig–Hornor reaction (Scheme ) without any precious metal catalysts, which only cost 4–5$ g –1 in laboratory synthesis (Table S1). The 1 H NMR and 13 C NMR spectra are shown in Figures S1–S10.…”

“…Figure a shows that the positive charges were delocalized on the whole molecules. In contrast to PtTA- m PV (Figure S13), the sulfur atoms on PsTA- m PV had negative charges, suggesting that the lone pair electrons of the sulfur atom would passivate the defects on the underlying surface of the perovskite due to the Lewis acid–base interaction. ,− To further determine the interactions between the perovskite and PsTA- m PV, 4-(methylthio)- N , N -diphenylbenzenamine (sTA) as the model molecule of the polymer was used to probe the interaction between the sulfur atom and PbI 2 . 1 H NMR was characterized as shown in Figure b.…”

Tailored Polymeric Hole‐Transporting Materials Inducing High‐Quality Crystallization of Perovskite for Efficient Inverted Photovoltaic Devices

“…In addition, due to the use of precious metal catalysts in the synthesis process, most of polymeric HTMs are difficult to achieve truly low-cost. [23][24][25][26][27][28][29][30][31][32][33] Another main problem is the high hydrophobicity of PTAA with about 80-100° contact angle, as compared with the traditional wetting HTM-PEDOT:PSS (≈10°). [34] The no-wetting surface of PTAA shows less affinity with polar perovskite precursor solutions, and the poor film coverage during spin-coating leads to inferior device reproducibility.…”

“…In addition, due to the use of precious metal catalysts in the synthesis process, most of polymeric HTMs are difficult to achieve truly low‐cost. [ 23–33 ]…”