Multifunctional Molecular Design of a New Fulleropyrrolidine Electron Transport Material Family Engenders High Performance of Perovskite Solar Cells

Abstract

C 61 -butyric acid methyl ester remains indispensable as the electron transport material (ETM) for perovskite solar cells (PSCs), but its synthesis involves complicated multisteps with low productivity. In contrast, the potential of synthesizing simpler fulleropyrrolidine derivatives has long been overlooked, and little has been understood regarding their structuredependent effects on photovoltaic (PV) performance. Herein, seven novel fulleropyrrolidine derivatives (F1-F7) are deliberately designed, synthesized, and comprehensively characterized in both solution and thin-film states and subsequently investigated as ETMs for PSCs. Notably, the F4 delivers the highest power conversion efficiencies over 20% of devices, which surpass all reported fulleropyrrolidine ETMs due to its optimal photoelectric property. Moreover, the structure-dependent effects of the fullerenes on PV parameters are uncovered, including solubility, intermolecular interaction, packing structure, and charge-transfer ability, which can guide the future design of highperformance and stable fullerene ETMs for PSCs.

Designing New Indene-Fullerene Derivatives as Electron-Transporting Materials for Flexible Perovskite Solar Cells

“…Size effects of the bulky functional groups can also influence intermolecular interactions of the neighboring carbon cages, which in turn could reflect in the reduction of electron mobility values, leading to electron extraction difficulties. 63 …”

Fullerene Derivative with Flexible Alkyl Chain for Efficient Tin-Based Perovskite Solar Cells

“…To balance the electron transportation and the physical entanglement between the fullerene molecules [ 35 ], we designed the fullerene derivative PCBH ( Scheme S1 ). We believed that the long alkyl chain would enhance the physical entanglement between PCBH molecules and elevate the stability of the film.…”

“…In addition, as shown in Figure 1 d, the introduction of the long alkyl chain increased the dipole moment of PCBH, which indicates that it has a larger dielectric constant. Therefore, the elevated dipole moment is expected to enhance the interface contact between PCBH and perovskite layers, as well as the mobility of the film [ 35 ].…”

“…The higher water resistance stability of the PCBH film may be attributed to the physical entanglement of the extended flexible alkyl chain, which leads to a denser film. The denser film of PCBH may have increased the electron transport and collection efficiency [ 35 ], as well as suppressing the potential of oxygen injection [ 42 , 43 ]. Therefore, we recorded the XPS Sn 3d spectra of the different perovskite films with the upper fullerene layer removed.…”

Tailoring Functional Terminals on Solution-Processable Fullerene Electron Transporting Materials for High Performance Perovskite Solar Cells

“…We designed and synthesized three fulleropyrrolidine derivatives, namely N -(2-cyanoethyl)-2-phenyl [60]fulleropyrrolidine (CEP), N -(2-cyanoethyl)-2-phenethyl [60]fulleropyrrolidine (CEPE), and N -(2-cyanoethyl)-2-(4-chlorobutyl) [60]fulleropyrrolidine (CECB), respectively, as shown in Figure 1 a. The synthetic routes and purification methods were described in Schemes S1–S3 in the Supporting Information [ 30 ]. All chemical structures were confirmed by 1 H NMR, 13 C NMR, and mass spectrometry ( Figures S1–S8 ).…”