Interfacial Engineering with Cross-Linkable Fullerene Derivatives for High-Performance Perovskite Solar Cells

Abstract

Two fullerene derivatives with styryl and oxetane cross-linking groups served as interfacial materials to modify an electron-transporting layer (ETL) of TiO, doped with Au nanoparticles, processed under low-temperature conditions to improve the performance of perovskite solar cells (PSC). The cross-linkable [6,6]-phenyl-C-butyric styryl dendron ester was produced via thermal treatment at 160 °C for 20 min, whereas the cross-linkable [6,6]-phenyl-C-butyric oxetane dendron ester (C-PCBOD) was obtained via UV-curing treatment for 45 s. Both cross-linked fullerenes can passivate surface-trap states of TiO and have also excellent surface coverage on the TiO layer shown in the corresponding atomic force microscopy images. To improve the crystallinity of perovskite, we propose a simple co-solvent method involving mixing dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) in a specific ratio (DMF/DMSO = 90/10). The fullerene derivative layer between the ETL and perovskite layers significantly improved electron extraction and suppressed charge recombination by decreasing the density of traps at the ETL surface. A planar PSC device was fabricated with the configuration indium tin oxide/TiO (Au)/C-PCBOD/perovskite/spiro-OMeTAD/Au to attain a power conversion efficiency (PCE) of 15.9%. The device performance was optimized with C-PCBOD as an interfacial mediate to modify the surface of the mesoporous TiO ETL; the C-PCBOD-treated device attained a significantly enhanced performance, PCE 18.3%. Electrochemical impedance spectral and photoluminescence decay measurements were carried out to understand the characteristics of electron transfer and charge recombination of the perovskite/TiO samples with and without a fullerene interfacial layer.

Causes and Solutions of Recombination in Perovskite Solar Cells

“…The ratio of PMMA to PCBM was found to be critical for achieving high PCE and from the optimal ratio of PMMA:PCBM = 1:3 the PCE was increased from 19.6% to 20.4% (Figure b) and the hysteresis was thoroughly suppressed (Figure c,d). Except for PCBM, other fullerene derivatives (such as C‐PCBOD, C‐PCBSD, and PCBB‐2CN‐2C8) were also developed to modify the perovskite/TiO 2 interface . Graphene is also candidate, where Zhao et al reported the modification of SnO 2 with graphene modified chemically by N , N ′‐bis‐[2‐(ethanoic acidsodium)]‐1,4,5,8‐naphthalene diimide (NDI) surfactant for normal planar PSCs.…”

Room‐Temperature‐Processed Fullerene/TiO2 Nanocomposite Electron Transporting Layer for High‐Efficiency Rigid and Flexible Planar Perovskite Solar Cells

“…[ 28–37 ] The fullerene derivative acts to improve electron transfer at the TiO 2 /PSK interface by lowering the interfacial resistance, reducing the nonradiative recombination channels (trap/defect sites) at the interface, blocking holes, and increasing the surface hydrophilicity to deposit good‐quality PSK films. [ 28–33,33–37 ] Furthermore, it was also shown that the light‐soaking instability of PSCs mainly originates from charge accumulation at the TiO 2 /PSK interface, which can be eliminated by interfacial modifications with a layer of fullerene. [ 33 ] Therefore, inserting an interlayer of fullerene between the TiO 2 ETL and PSK can also improve the long‐term stability of the cell.…”

Targeted Molecular Design of Functionalized Fullerenes for High‐Performance and Stable Perovskite Solar Cells

“…[ 51 ] Likewise, cross‐linkable [6,6]‐phenyl‐C 61 ‐butyric styryl dendron ester (c‐PCBSD) was also demonstrated in regulating interfacial energy as well as electronic quality of perovskite layers, contributing to high efficiency, fully solution‐processed and flat junction solar cell. [ 52 ] Amassian et al further deposited a mesostructured cross‐linking PCBM on the mesoporous TiO 2 layer, which can both enhance the structural and electronic properties of the perovskite layer grown atop. [ 53 ] More importantly, the cross‐linking strategy conduced to the long‐term stability of fullerene ETLs by inhibiting morphological changes and aggregation of fullerenes.…”