One-Step Synthesis of TiO₂/Graphene Nanocomposites by Laser Pyrolysis with Well-Controlled Properties and Application in Perovskite Solar Cells

Abstract

This work presents an original synthesis of TiO 2 /graphene nanocomposites using laser pyrolysis for the demonstration of efficient and improved perovskite solar cells. This is a one-step and continuous process known for nanoparticle production, and it enables here the elaboration of TiO 2 nanoparticles with controlled properties (stoichiometry, morphology, and crystallinity) directly grown on graphene materials. Using this process, a high quality of the TiO 2 /graphene interface is achieved, leading to an intimate electronic contact between the two materials. This effect is exploited for the photovoltaic application, where TiO 2 /graphene is used as an electron-extracting layer in n–i–p mesoscopic perovskite solar cells based on the reference CH 3 NH 3 PbI 3– x Cl x halide perovskite active layer. A significant and reproducible improvement of power conversion efficiencies under standard illumination is demonstrated, reaching 15.3% in average compared to 13.8% with a pure TiO 2 electrode, mainly due to a drastic improvement in fill factor. This beneficial effect of graphene incorporation is revealed through pronounced photoluminescence quenching in the presence of graphene, which indicates better electron injection from the perovskite active layer. Considering that a reduction of device hysteresis is also observed by graphene addition, the laser pyrolysis technique, which is compatible with large-scale industrial developments, is therefore a powerful tool for the production of efficient optoelectronic devices based on a broad range of carbon nano-objects.

Carbon/Graphene-Modified Titania with Enhanced Photocatalytic Activity under UV and Vis Irradiation

“…Titania (TiO 2 (C)) and graphene-modified titania (G-TiO 2 (C)) were prepared by laser pyrolysis. This synthesis technique has already been described in several publications, e.g., Pignon et al for the synthesis of TiO 2 with controlled anatase to rutile ratio and Belchi et al for the one-step synthesis of graphene/TiO 2 nanocomposites [25,26]. A schematic drawing of the experimental set-up is shown in Figure 1, and the most salient features of the technique are described hereafter.…”

“…SEM and TEM images of graphene, TiO2(C) and G-TiO2(C) samples are given in Figure 2 Original graphene sheets and graphene sheets covered with fine NPs of titania are shown in Figure 2a The samples formed by the laser pyrolysis were grey, due to the presence of significant content of carbon (ca. 25% [25]) from titania precursor (TTIP) and C 2 H 4 (a pyrolysis sensitizer). Although the previous study indicates the disappearance of the grey color after annealing (430 • C for 6 h; The conditions were estimated carefully to remove carbon impurities, and to avoid graphene combustion [25]), annealed samples were still greyish, probably due to different geometric conditions in a new furnace (KDF S-70; Denken-High Dental Co., Ltd.).…”

“…25% [25]) from titania precursor (TTIP) and C2H4 (a pyrolysis sensitizer). Although the previous study indicates the disappearance of the grey color after annealing (430 °C for 6 h; The conditions were estimated carefully to remove carbon impurities, and to avoid graphene combustion [25]), annealed samples were still greyish, probably due to different geometric conditions in a new furnace (KDF S-70; Denken-High Dental Co., Ltd.). The respective photoabsorption spectra before and after annealing are shown in Figure 3a Similar photoabsorption spectra have already been reported for C-modified titania, prepared from TTIP by the sol-gel method and calcination at 350 °C [17].…”

“…Our recent study on graphene-modified titania has shown that this material might be efficiently used for perovskite solar cells, where graphene presence enhanced power conversion efficiency significantly, as a result of photoluminescence quenching, due to enhanced electron migration [25]. Therefore, to further examine the potential and application possibility of graphene-modified titania, prepared by a novel and simple method using laser pyrolysis, more detailed characterization and photocatalytic activity for degradation of organic compounds, hydrogen evolution and microorganism inactivation under both UV and vis irradiation have been investigated in this study.…”

Electrodeposited ZnO nanoparticles on vertically aligned carbon nanotubes (VACNTs) as promising charge extracting electrodes for halide perovskite devices

“…Usually, electron collection is ensured by the use of a selective contact layer composed of semiconducting oxide such as TiO 2 , ZnO or SnO 2 and one of the strategies explored in the literature to enhance the charge collection efficiency of PSCs is the addition of carbon nano-objects, such as graphene materials, in a small amount. [4][5][6][7] Among these carbon nanoobjects, carbon nanotubes (CNTs) have sparked very active research since the 2000s in the case of polymer nanocomposites to improve mechanical and electrical properties, 8 and particularly in the case of organic solar cells. 9 For this latter application, the predominant idea was to exploit the photoinduced charge transfer between a conjugated polymer absorber and the CNTs whose anisotropy should favour the transport and the collection of the charges towards the electrodes.…”