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

Abstract

Room-temperature-processed TiO 2 (R-Lt-TiO 2) electron transporting layers (ETLs) possess low conductivity and connectivity, resulting in poor photovoltaic performance. Herein, an ethanol (EtOH)-soluble, highly conducting fullerene derivative, C 60 RT 6 , was used as an additive for Lt-TiO 2 ETLs. Room-temperature processed nanocomposite ETL (R-Fu/Lt-TiO 2) is prepared simply by spin coating a C 60 RT 6 and G-TiO 2 NPs (TiO 2 nanoparticle prepared by grinding the bulk TiO 2 powder) mixture. R-Fu/Lt-TiO 2 has better aligned with the frontier orbitals of the FA x MA 1Àx PbI 3 , better continuity, conductivity, flatness, and higher surface hydrophilicity compared to Lt-TiO 2 ETL. Perovskite films spin coated on R-Fu/ Lt-TiO 2 ETLs also have slightly larger grains and thickness compared to those deposited on Lt-TiO 2. Perovskite solar cells (PSCs) based on a R-Fu/Lt-TiO 2 ETL possess higher power conversion efficiency (PCE, up to 20% on glass substrate), less (negligible) current hysteresis, and better long-term stability compared to those using R-Lt-TiO 2 as an ETL. The flexible PSC (used indium tin oxide/ polyethylene terephthalate (ITO/PET) as a substrate) with a R-Fu/Lt-TiO 2 ETL achieves a PCE of 18.06% and retains 90% of the initial PCE after 500 bending cycles with a bending radius of 6 mm. The PCE of the flexible cell with a Lt-TiO 2 ETL is only 8.2%, and loses 60% of the initial value after 500 bending cycles.

Low‐Temperature‐Processed Stable Perovskite Solar Cells and Modules: A Comprehensive Review

“…Therefore, an ethanol-soluble ionic fullerene derivative was added to improve the conductivity, achieving efficiencies of 18.92% and improved long-term stability under room light illumination of 1000 lux. [52] Recently, Miyasaka's group demonstrated a low-temperature (<130 °C) niobium-doped titanium oxide compact layer coupled with brookite TiO 2 mesoporous layer resulted in a PCE of 19.8%. [53] However, these devices show large hysteresis and relatively low stabilities.…”

Hole-Transport-Underlayer-Induced Crystallization Management of Two-Dimensional Perovskites for High-Performance Inverted Solar Cells

“…To address this issue, it is necessary to improve the performance of conventional perovskites and develop new perovskites with better intrinsic stability. − Currently, Ruddlesden–Popper two-dimensional (2D) perovskites have drawn intensive attention because of their excellent stability and tunable band alignment. − Although the PCE of 2D perovskite (Ruddlesden–Popper-type)-based solar cells is still lower than that of conventional 3D perovskite-based devices, long stability can be dramatically enhanced. , For instance, (BA) 2 (MA) n −1 Pb n I 3 n +1 perovskite series ( n represents an integer and BA means CH 3 (CH 2 ) 3 NH 3 )) has been frequently adopted as an absorber for fabricating PSCs, demonstrating a high PCE of above 10%. − Based on the locations of electrodes and charge-transporting layers, PSCs can be made into regular (n-i-p) and inverted (p-i-n) structures. , Generally, a composite of compact and mesoporous TiO 2 is prepared as an electron transport layer (ETL) for regular structured PSCs. , However, sintering TiO 2 needs a temperature as high as 500 °C, which is detrimental to large-scale production. , Moreover, the photocatalytic effect of TiO 2 may facilitate the decomposition of perovskite under the exposure of ultraviolet–visible (UV) light . As a result, inverted structured PSCs are considered more suitable for commercialization, in which usually phenyl-C 61 -butyric acid methyl ester (PCBM) is used as the ETL. − In case of a hole-transport layer (HTL), generally, some organic semiconductors are widely used, such as poly­(3,4-ethylenedioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), poly­(bis­(4-phenyl)­(2,4,6-trimethylphenyl)­amine) (PTAA), poly­(3-hexylthiophene-2,5-diyl) (P3HT), and 2,2′,7,7′-tetrakis-( N , N -di- p -methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD), − which are also widely used for 2D PSCs.…”

“…4,8 However, sintering TiO 2 needs a temperature as high as 500 °C, which is detrimental to large-scale production. 24,25 Moreover, the photocatalytic effect of TiO 2 may facilitate the decomposition of perovskite under the exposure of ultraviolet−visible (UV) light. 26 As a result, inverted structured PSCs are considered more suitable for commercialization, in which usually phenyl-C 61 -butyric acid methyl ester (PCBM) is used as the ETL.…”

Synergistic Engineering of Conduction Band, Conductivity, and Interface of Bilayered Electron Transport Layers with Scalable TiO2 and SnO2 Nanoparticles for High-Efficiency Stable Perovskite Solar Cells

“…The electron transport layer (ETL) that extracts and transports the photogenerated electrons and blocks the holes from the perovskite (Psk) absorber plays an indispensable role in the photovoltaic performance of a PSC. Searching for suitable ETL materials and processes for PSCs has been a significant effort in the PSC community. − Titanium dioxide (TiO 2 ) films have been the most widely employed ETLs in regular PSCs, because of their wide band gap, high chemical stability, easy preparation, long electron lifetime, and frontier orbital energy levels being compatible with Psk absorbers, and they are also an abundant, nonexpensive, nontoxic material . Furthermore, PSCs based on a low (≤100 °C) temperature-processed (to save energy and reduce the fabrication cost as well as to be applied in organic polymer-based flexible electrodes) TiO 2 (Lt-TiO 2 ) ETL were proved to have a high power conversion efficiency (PCE) of over 17% .…”