Less Is More: Simplified Fluorene-Based Dopant-Free Hole Transport Materials Promote the Long-Term Ambient Stability of Perovskite Solar Cells

Abstract

The stability of perovskite solar cells (PSCs) is greatly affected by the interface between the perovskite active layer and the hole transport material (HTM). The rational design of HTMs with effective anchoring to the perovskite surface is an emerging elegant strategy to promote compact and ordered interfaces that lead to highly efficient and stable PSCs. Herein, we propose two fluorene-based HTM molecular architectures (SCF1 and SCF2) derived from the popular yet expensive Spiro-OMeTAD. Their employment as dopant-free HTMs in standard triple-cation CsFAMA PSCs leads to superior device stability, with a T 80 lifetime well above 1 year (431 days). Our combined theoretical and experimental study of the CsFAMA|HTM interface reveals that the improved adhesion of the SCF-HTMs to the perovskite layer is the key to minimize the non-radiative recombination, reduce the hole trap density, and enhance the long-term stability of the corresponding devices. The simplified structures of SCF1 and SCF2, obtained by removing the orthogonal fragment of the Spiro-OMeTAD scaffold, show a lower molecular distortion than Spiro-OMeTAD, thus promoting a favorable electronic interaction between the SCF-HTMs and the perovskite. This study provides useful design criteria for achieving highly stable PSCs including dopant-free HTMs with optimized adhesion to the perovskite surface.

Antimony‐Bismuth Alloying: The Key to a Major Boost in the Efficiency of Lead‐Free Perovskite‐Inspired Photovoltaics

“…The same approach had been successfully applied to different systems. [57,72,73] The 𝜖 values (4.89 and 4.79 for CABI and CABI-Sb, respectively) were estimated using the many bodies perturbation theory in the random phase approximation (the data was presented in Figure S18, Supporting Information).…”

Organic fluorophore-substituted polyaza-[7]helicenes derived from 1,10-phenanthroline: Studying the chromophoric effect on fluorescence efficiency

“…2,9-Dichloro-1,10-phenanthroline ( 4 ) was synthesized following previous literature. 35,36 1,10-Phenanthroline was subjected to nucleophilic substitution reaction resulting in the intermediate 2 in good yield. Compound 3 resulted from the oxidation reaction of intermediate 2 in the presence of potassium tert -butoxide in good yield.…”

“…This indicates that all the aza-[7]helicenes are suitable for the hole transporting process in PSCs applications. 36,37 Thus, the introduction of fluorene, carbazole and triphenylamine units on aza-[7]helicene can improve several optoelectronic properties, such as quantum yield, maximum wavelength ( λ max ), molar extinction coefficient ( ε ), band gap ( E g ) and fluorescence emission ( λ em ) of molecules, due to strong push–pull effect between the donor and aza-[7]helicene moiety.…”

Benzodithiophene‐Based Copolymers as Dopant‐Free Hole‐Transporting Materials for Perovskite Solar Cells

“…High PCEs are often achieved in PSCs using doped spiro-OMeTAD. [34] Hence, the paramount goal is the development of dopant-free HTMs with easily accessible synthesis routes, operational stability, well-aligned HOMO energy levels, and commendable hole mobility. Many of these molecules feature central conjugated π-electron cores, including structures such as thiophenes, fused thiophenes, spiro compounds, pyrenes, and donorslike diphenylamines, triphenylamines, carbazoles, and so forth.…”