Titanium dioxide (TiO2) is an extensively used electron transporting layer (ETL) in n–i–p perovskite solar cells (PSCs). Although, TiO2 ETL experiences the high surface defect together with low electron extraction ability, which causes severe energy loss and poor stability in the PSC. In this study, a new intermediate layer consisting of gold nanoparticles functionalized with fully conjugated fullerene C60 derivative (C60‐BCT@Au NPs) that enhances the interfacial contact at ETL/perovskite interface leading to a perovskite film with improved crystallinity and morphology is reported. Moreover, the studies demonstrate that the interface modification of the TiO2 ETL with C60‐BCT@Au NPs substantially improves the charge extraction efficiency from the perovskite layer and suppresses charge recombination processes. Consequently, the resulting device yields a champion efficiency of 19.08% as well as devaluation in hysteresis. In addition, the unencapsulated PSCs with c‐TiO2/C60‐BCT@Au NPs ETL retain 83% and 90% of their original PCEs after 500 h storage in air and exposure to continuous UV illumination for 200 h, respectively. This study provides an effective method to address the electron transporting issues between perovskite and c‐TiO2 ETL for developing stable and efficient PSCs.

We report a highly electron-absorbing material (“electron-sponge”) obtained by coupling gold nanoparticles (AuNPs, 8 nm in diameter) with fullerene C60 spheres by fully conjugated linker molecules. This goal has been achieved through synthesis of a new class of conducting thionoester-substituted and thioketone-substituted azahomo-[60]­fullerenes. The obtained C60 derivatives have been found to possess the capability of binding covalently to the surface of gold. Thus, for the first time, we show that thioketone and thionoester moieties can be successfully employed as new anchoring groups for conjugated fullerene derivatives. High-resolution X-ray photoelectron spectroscopy studies have revealed that the ligands are attached to the gold surface of AuNPs through strong Au–S bonding. One of the synthesized C60 derivatives, O-butyl 4-(azahomo­(C60-Ih)­fullerene)­benzothioate (C60-BCT-OBu), has been investigated in detail. The C60-BCT-OBu-coated AuNPs form a highly insoluble precipitate, which can be easily dissolved in toluene into individual AuNPs using cationic surfactants. The precipitate has been found to exhibit an extraordinary capability of absorbing electrons. A single AuNP can absorb on average about 4500 electrons in an experimental condition in which tetrahydrofuran suspension of the precipitate of the C60-BCT-OBu-coated AuNPs is charged in a lithium naphthalide-mediated process. The electrical properties of the AuNPs are successfully explained by a model in which the C60-BCT-OBu-coated AuNP is represented by an equipotential heterostructure composed of C60 spheres connected with the gold AuNP core by conducting linkers.

Fullerene derivatives with a strong electron-accepting ability play a crucial role in enhancing both the performance and stability of perovskite solar cells (PSCs). However, most of the used fullerene molecules are based on [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which limits the device performance due to difficulties in preparing high-quality and uniform thin films. Herein, solution-processable azahomofullerene (AHF) derivatives (abbreviated as AHF-1 and AHF-2) are reported as novel and effective electron-transport layers (ETLs) in p–i–n planar PSCs. Compared to the control PCBM ETL-based PSCs, the devices based on AHFs exhibit higher photovoltaic performances, which is attributed to the enhanced charge-transport properties and improved layer morphology leading to a maximum power conversion efficiency (PCE) of 20.21% in the case of the device based on AHF-2 ETL. Besides, due to the preferable energy band alignment with the perovskite layer, reduced trap states, and suppressed charge recombination, the device with AHF-2 ETL exhibits significantly suppressed hysteresis and improved stability under both ambient and thermal conditions.