Powder pressed cuprous iodide (CuI) as a hole transporting material for perovskite solar cells

This study focuses on employing cuprous iodide (CuI) as a hole-transporting material (HTM) in fabricating highly efficient perovskite solar cells (PSCs). The PSCs were made in air with either CuI or 2,2′,7,7′-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9′-spirobifluorene (spiro-OMeTAD) as HTMs. A simple and novel pressing method was employed for incorporating CuI powder layer between perovskite layer and Pt top-contact to fabricate devices with CuI, while spiro-OMeTAD was spin-coated between perovskite layer and thermally evaporated Au top-contact to fabricate devices with spiro-OMeTAD. Under illuminations of 100 mW/cm2 with an air mass (AM) 1.5 filter in air, the average short-circuit current density (JSC) of the CuI devices was over 24 mA/cm2, which is marginally higher than that of spiro-OMeTAD devices. Higher JSC of the CuI devices can be attributed to high hole-mobility of CuI that minimizes the electron-hole recombination. However, the average power conversion efficiency (PCE) of the CuI devices were lower than that of spiro-OMeTAD devices due to slightly lower open-circuit voltage (VOC) and fill factor (FF). This is probably due to surface roughness of CuI powder. However, optimized devices with solvent-free powder pressed CuI as HTM show a promising efficiency of over 8.0 % under illuminations of 1 sun (100 mW/cm2) with an air mass 1.5 filter in air, which is the highest among the reported efficiency values for PSCs fabricated in an open environment with CuI as HTM

Natural Dye-Sensitized Solar Cells: Fabrication, Characterization, and Challenges

Bio-inspired dye-sensitized solar cells (DSSCs) from natural plant-based dyes gained importance due to their low cost of manufacturing and environmental friendliness. Not all plants are candidates for DSCCs; they should contain certain pigments such as chlorophyll, anthocyanin, and betalains. Titanium oxide nanoparticles play an important role as electron transporter in the DSSCs. The efficiency is still low in comparison with traditional silicon-based solar cells. There are several challenges to improve the efficiency such as the photodegradation of the dye, the stability of the electrolyte over time, and adhesion of dye with titanium oxide nanoparticles. We reviewed methods for fabricating DSSCs, and the science behind the working principle. Various microscopic and spectroscopic analysis methods such as Fourier transform infrared spectroscopy and confocal microscopy were presented, for investigating optical properties, surface chemistry of the dyes, and in structural characterization of the plant cells. The photoelectrochemical properties such as conversion efficiency measure the performance of the DSSCs. They are usually in the range of 0.05–3.9% depending on the plant dye used, including plant dyes modified. A critical feature in the design of dye-sensitized solar cells is the attachment of the photosensitizing dye to the titanium oxide surface. We reviewed and summarized the design of binding elements that enhance the binding of the sensitizing dye to the titanium dioxide surface. The efficiencies of covalent linkage of the dye to the titanium surface versus non-covalent binding were discussed, including a survey of functional groups and geometries, to determine the most effective reported