Inverted organic solar cells with non-clustering bathocuproine (BCP) cathode interlayers obtained by fullerene doping

Bathocuproine (BCP) is a well-studied cathode interlayer in organic photovoltaic (OPV) devices, where it for standard device configurations has demonstrated improved electron extraction as well as exciton blocking properties, leading to high device efficiencies. For inverted devices, however, BCP interlayers has shown to lead to device failure, mainly due to the clustering of BCP molecules on indium tin oxide (ITO) surfaces, which is a significant problem during scale-up of the OPV devices. In this work, we introduce C₇₀ doped BCP thin films as cathode interlayers in inverted OPV devices. We demonstrate that the interlayer forms smooth films on ITO surfaces, resulting from the introduction of C₇₀ molecules into the BCP film, and that these films possess both improved electron extraction as well exciton blocking properties, as evidenced by electron-only devices and photoluminescence studies, respectively. Importantly, the improved cathode interlayers leads to well-functioning large area (100 mm²) devices, showing a device yield of 100%. This is in strong contrast to inverted devices based on pure BCP layers. These results are founded by the effective suppression of BCP clustering from C₇₀, along with the electron transport and exciton blocking properties of the two materials, which thus presents a route for its integration as an interlayer material towards up-scaled inverted OPV devices.

Deposition of zinc oxide as an electron transport layer in planar perovskite solar cells by spray and SILAR methods comparable with spin coating

CH₃NH₃PbI₃ planar-structure perovskite solar cells were fabricated with the configuration FTO/ZnO/CH₃NH₃PbI₃/Au. ZnO nanoparticles were synthesized by the precipitation method. Three different deposition methods including spin-coating, spraying and successive ionic layer adsorption and reaction (SILAR) were applied to fabricate the ZnO films as electron transport layers. Certain analyses, such as XRD, SEM, FESEM, UV-visible and I–V measurements, were carried out to evaluate the performance of the cells. The best cell performance was achieved for the perovskite solar cell with a ZnO film coated by the spin method. The average efficiency was 7% without using any hole transport materials and 10.25% using spiro-OMeTAD as a hole transport material. The average efficiencies of the cells coated by the spraying and SILAR methods using spiro-OMeTAD, were found to be 8.64% and 7.7% respectively. This study demonstrates the versatility of the spray and SILAR coating methods and their potential for fabricating low-cost, large scale, flexible and mass produced perovskite solar cells.

We have examined the versatility of spray and SILAR coating methods in fabricating mass produced low cost efficient planar perovskite solar cells.

Optical Optimization of the TiO2 Mesoporous Layer in Perovskite Solar Cells by the Addition of SiO2 Nanoparticles

In this work, SiO₂ nanoparticles (NPs) were integrated into the mesoporous TiO₂ layer of a perovskite solar cell to investigate their effect on cell performance. Different concentrations of SiO₂/ethanol have been combined in TiO₂/ethanol to prepare pastes for the fabrication of the mesoporous layer with which perovskite solar cells have been fabricated. Addition of SiO₂ NPs of 50 and 100 nm sizes produces an enhancement of cell performance mainly because of an improvement of the photocurrent. This increment is in good agreement with the theoretical predictions based on light scattering induced by dielectric SiO₂ NPs. The samples using modified scaffolds with NPs also present a significant lower current-potential hysteresis indicating that NP incorporation also affects the ion accumulation at the perovskite interface, providing an additional beneficial effect. The results stress the importance of the appropriated management of the optical properties on further optimization of perovskite solar cell technology.

Inorganic Surface Engineering to Enhance Perovskite Solar Cell Efficiency

The photoconversion efficiency of perovskite solar cells (PSCs) is enhanced by the deposition of inorganic nanoparticles (NPs) at the interface between the compact TiO₂ electron-selective contact and the mesoporous TiO₂ film. The NPs used are core/shell Au@SiO₂, where a thin SiO₂ coating protects the Au core from the direct chemical interaction with CH₃NH₃PbI₃ halide perovskite used as light-harvesting material. The samples prepared with Au@SiO₂ NPs exhibit a higher external quantum efficiency in the complete wavelength range at which perovskite presents light absorption and not just at the wavelengths at which Au@SiO₂ NPs present their absorption peak. This fact rules out a direct plasmonic process as responsible for the enhancement of cell performance. A detailed characterization by photoluminescence, impedance spectroscopy, and open-circuit voltage decay unveils a modification of the interfacial properties with an augmentation of the interfacial electrostatic potential that increases both photovoltage and photocurrent. This article highlights the dramatic role of interfaces in the performance of PSCs. The use of reduced quantities of highly stable inorganic compounds to modify the PSC interface instead of the extensively used organic compounds opens the door to a new surface engineering based on inorganic compounds.

Preconcentration, speciation and determination of ultra trace amounts of mercury by modified octadecyl silica membrane disk/electron beam irradiation and cold vapor atomic absorption spectrometry

Mercury (II) and methyl mercury cations at the Sub-ppb level were adsorbed quantitatively from aqueous solution onto an octadecyl-bonded silica membrane disk modified by 2-[(2-mercaptophyenylimino)methyl] phenol (MPMP). The trapped mercury was then eluted with 3ml ethanol and Hg2+ ion was directly measured by cold vapor atomic absorption spectrometry, utilizing tin (II) chloride. Total mercury (Hgt) was determined after conversion of MeHg+ into Hg2+ ion by electron beam irradiation. A sample volume of 1500ml resulted in a preconcentration factor of 500 and the precision for a sampling volume of 500ml at a concentration of 2.5microgl(-1) (n=7) was 3.1%. The limit of detection of the proposed method is 3.8ngl(-1). The method was successfully applied to analysis of water samples, and the accuracy was assessed via recovery experiment.