• Energy Research

AbstractHybrid organic–inorganic perovskite solar cells (PSCs) are one of the most promising candidates for next generation photovoltaics. Further improvement in their performance, particularly efficiency, durability and reproducibility, requires a deep understanding of recombination losses during fabrication and within a device itself. In this work, we report a contactless, imaging‐based procedure to spatially resolve electronic properties of PSCs including implied open‐circuit voltage (iVoc) and its temperature coefficient, ideality factor (nid) and activation energy of recombination (EA) by employing illumination intensity and temperature‐dependent photoluminescence. The illumination intensity dependence of iVoc allows the extraction of nid whereas its temperature dependence allows the extraction of the temperature coefficient and EA. This imaging approach is then applied to investigate changes of these electronic parameters on fully and partially fabricated devices.

The light scattering and harvesting effects in dye‐sensitized solar cells (DSSCs) is studied by controlling morphology, phase composition, and thickness of monolayer and double‐layer TiO2 photoanode electrodes. The starting materials for preparation of TiO2 cells, including 25 nm mesoporous anatase nanoparticles, 200 nm anatase microspheres, 10 µm dandelion‐like rutile particles and 40 nm nanoparticles containing 80% anatase‐20% rutile, are synthesized by evaporation‐induced self‐assembly, sol‐gel, and hydrothermal processes. It was found that the mesoporous anatase nanoparticles may improve light harvesting and dye‐sensitization due to their high surface area and small particle size, whereas the microspheres and dandelion‐like particles can enhance light scattering effect. The improvement of light harvesting efficiency is obtained by controlling the microstructure and thickness of photoanode electrode to increase dye adsorption. This is achieved by preparation of high surface area TiO2 monolayer film with optimum thickness and good connections between the particles using mesoporous anatase nanoparticles. The influence of film's thickness on photovoltaic characteristics of monolayer DSSCs shows that the optimal thickness around 30 μm results in the highest cell efficiency of 6.31%. The enhancement of light scattering is acheieved by design of a proper scattering layer with desired morphology and phase composition. The dye loading property of the scattering layer is also considered simultaneously. The photovoltaic characteristics of double‐layer DSSCs, with total thickness of 30 µm, reveal that the cell efficiency enhances up to 7.54 and 8.91% using a mixture of dandelion‐like particles and mesoporous nanoparticles and microspheres and mesoporous nanoparticles, respectively. © 2016 American Institute of Chemical Engineers Environ Prog, 35: 1818–1826, 2016

Abstract A novel and efficacious strategy was implemented for creation of mesoporous TiO2 films and powder through an integration of sol–gel and evaporation-induced self-assembly (EISA) processes aided by triblock Pluronic P123. A mesoporous crack-free thin film with virtual thickness of 300 nm was attained under 10% relative humidity aging, for 72 h at the low temperature of 5 °C. Further, the TiO2 film with porous structure has been formed from conventional paste, exploiting as-prepared mesoporous titania powder. The X-ray Diffraction (XRD) of synthesized mesoporous powder disclosed formation of anatase phase as well as rutile phase, in such a manner that the latter constituted a very small minority. Moreover, Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Helenda (BJH) proved that the isotherm pertaining to synthesized powder implies a combination of types II and IV which are related to mesoporous material with average pore size of 5.8 nm and BET surface area of 114 m2/g. Owing to the quantum size effect, diffuse reflection spectroscopy of prepared mesoporous TiO2 powder denoted a blue shift by comparison with that of bulk TiO2. The mesoporous TiO2 film which has been prepared under optimized circumstances, possesses appropriate microstructural and optical properties so that it can be utilized for dye-sensitized solar cell (DSSC) applications. In order to delve profoundly into the effect of TiO2 thin film, two types of monolayer and doublelayer DSSCs were made. In light of the achieved results, the doublelayer cell indicated superior power conversion efficiency and short circuit current density of 8.05% and 18.27 mA/cm2, respectively.