Boosting of the Performance of Perovskite Solar Cells through Systematic Introduction of Reduced Graphene Oxide in TiO2 Layers

Abstract

The effects of the inclusion of reduced graphene oxide (RGO) in TiO 2 layers on performance of perovskite solar cells were systematically investigated. For this purpose, a wet chemical approach was examined to embed graphene oxide (GO) across the thickness of compact TiO 2 (cTiO 2 ) and mesoporous TiO 2 (mTiO 2 ) layers, which was followed by a thermally driven in situ conversion from GO to RGO. The presence of RGO at loadings of 0.15 wt % in the cTiO 2 layer and of 0.015 wt % in the mTiO 2 layer led to a power conversion efficiency (PCE) from 6.6% to 9.3% by 40% increase.In the last few years, solar cells based on organicinorganic hybrid halide perovskites (e.g., methylammonium lead halides CH 3 NH 3 PbX 3 , where X = halogen) have witnessed tremendous growth and continued to attract a huge interest.1 A typical cell architecture consists of a perovskite light-absorbing layer sandwiched between a hole-transporting material (HTM) 2,3 and electron-transporting compact TiO 2 (cTiO 2 ) layers. Mesoporous TiO 2 (mTiO 2 ) scaffolds are frequently integrated as the electron conduction pathway especially when a typical triiodide perovskite without other halides (CH 3 NH 3 PbI 3 ) is used, because the carrier diffusion length of CH 3 NH 3 PbI 3 is too short (ca. 100 nm) 4 to collect the carrier generated in the perovskite layer 5 effectively at the electrode. Nevertheless, the relatively slow electron diffusion through TiO 2 layers limits the charge conduction in the solar cells when combined with HTM with high hole conductivity such as doped 2,2¤,7,7¤-tetrakis(N,N-bis(p-methoxyphenyl)amino)-9,9¤-spirobifluorene (spiro-OMeTAD).6 For the improvement of device performances, maximizing the charge-transport properties in TiO 2 layers is one of the leading challenges.To address this challenge, employing carbon-based materials is a promising option. Graphene is an ordered network of hexagonally-linked carbon atoms arranged with periodicity that aids rapid transport of electrons.7 Reduced graphene oxide (RGO) possesses some defects but is functionally similar to graphene.8 It demonstrates graphene-like properties including transportation of charges are amenable to functionalization, and more importantly, RGO is less expensive and easier to process than graphene.9 RGO has proven compatibility with metals, metal oxides, and organic materials. 10 The integration of RGO with photoactive materials by adapting simple synthetic strategies offers immense advantages to cost-effective processing and device development.A recent report investigating the role of graphene in perovskite solar cells based on cTiO 2 and mesoporous Al 2 O 3 layers suggests that graphene incorporation in cTiO 2 layer lowers interfacial resistance between the cTiO 2 layer and FTO (fluorinedoped tin oxide) promoting charge transport.11 In addition, there are a few reports on the enhanced efficiencies of dye-sensitized solar cells by using graphenenanostructured TiO 2 composites as photoanode materials.12 On the basis of these reports and the observation involving...

Graphene–Perovskite Solar Cells Exceed 18 % Efficiency: A Stability Study

“…Apart graphene, other 2D crystals, such as chemically modified graphene [e.g., graphene oxide (GO) [49] and reduced graphene oxide (RGO)], [50] or inorganic 2D crystals, [47] such as transition metal dichalcogenides or transition metal oxides, offering complementary (opto)electronic properties to graphene, [47] are also promising interface materials. [57] This permits to use GRMs, in the graphene-based oxidized form (GO or RGO), as dopant [58][59][60] and as interlayer, [61,62] with the aim to enhancec harge injection at the counter electrode. [55,56] GRMs are very versatile, offering ap ossibility to control the bandgap andb and alignment through chemical functionalization and edge modification.…”

“…[55,56] GRMs are very versatile, offering ap ossibility to control the bandgap andb and alignment through chemical functionalization and edge modification. [57] This permits to use GRMs, in the graphene-based oxidized form (GO or RGO), as dopant [58][59][60] and as interlayer, [61,62] with the aim to enhancec harge injection at the counter electrode. Moreover,t he use of liquid-phasee xfoliated (LPE) graphene flakes, [63] as well as graphene produced by bottom-up approaches, [64][65][66][67] can boost the charge-transport dynamics at the photo electrode (PE).…”

Thermal Precursor Approach to Pristine Fullerene Film as Electron Selective Layer in Perovskite Solar Cells

“…40 nm between FTO and CH 3 NH 3 PbI 3 ( Figure 8). It should also be noted here that the cell configuration of FTO/C 60 /CH 3 NH 3 PbI 3 /HSL/Au allows establishment of a cascading energetics sequence (Figure 7b), [26][27][28][29]36 making it possible to derive the electrons and holes in the cell upon illumination.…”

“…To get insights into the better photovoltaic performances of the device with C 60 ESL than those with TiO 2 ESL, electrical impedance spectroscopy (EIS) measurements of the devices were performed in dark conditions ( Figure 13). 29,36,37 The Nyquist plot of the C 60 -based device exhibits a semicircle with much smaller size than that of the TiO 2 -based device. The smaller semicircle indicates a low chargetransfer resistance at the interface between the C 60 and CH 3 NH 3 PbI 3 in comparison with that at the TiO 2 -CH 3 NH 3 PbI 3 interface.…”

“…Fabrication of perovskite solar cells.-The perovskite solar cells were fabricated according to the reported procedure 36,37 with modifications as follows. A fluorine-doped tin oxide (FTO) glass (Nippon Sheet Glass, NSG TEC15, 15 /sq) was sonicated in a detergent solution (Semicoclean, Furuuchi Chemical) for 15 min, which was followed by consecutive washing with water, ethanol and acetone.…”