Thin-film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two-step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution-processed thin films yielded an average power conversion efficiency of 13.9±0.7% and a steady state efficiency of 13% under standard AM 1.5 conditions.

Thin‐film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low‐cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two‐step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one‐step, solvent‐induced, fast crystallization method involving spin‐coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution‐processed thin films yielded an average power conversion efficiency of 13.9±0.7 % and a steady state efficiency of 13 % under standard AM 1.5 conditions.

Mesoporous titania-based materials with a crystalline framework, high surface area and tunable pore size have received significant research attention due to the range of applications for such materials: photocatalysis, energy storage and conversion, electrochromic and sensing fields.[1] For a variety of practical applications, the fabrication of desired morphologies and textures is important as well as control in crystallinity, porosity and composition.[2] Mesoporous titania films, [3] beads, [4] monoliths, [5] networks, [6] and tubes [7] have been prepared via different synthesis strategies. Of particular interest are monodisperse TiO 2 beads with a submicrometer-sized diameter, because of their relatively high refractive index and comparative particle sizes to optical wavelengths, which make them ideal candidates for photon-related applications such as photocatalysis, [4c-g] dyesensitized solar cells (DSSC), [4h] and photonic crystals.[8]As a promising alternative to conventional silicon-based solar cells, high performance DSSCs have been extensively studied in recent years.[9] For an efficient DSSC, the porous electrode composed of anatase phase TiO 2 nanocrystals (% 20 nm) is essential due to the high internal surface area which maximizes the uptake of the dye molecules, thereby giving rise to DSSCs with large current density and high photon-to-current conversion efficiency.[10] However, such TiO 2 nanocrystal films usually show high transparency and negligible light scattering due to the small particle size and this results in poor light-harvest.[11] One approach to enhance the light-harvesting capability of the TiO 2 electrodes, without sacrificing the accessible surface for dye loading, is the use of submicrometer-sized TiO 2 beads with abundant mesopores. Such purpose-built mesoporous TiO 2 beads are expected to simultaneously promote light scattering and the dye loading of the electrodes, thereby increasing the photon-to-current conversion efficiency. However, to our knowledge, few reports addressing this issue have been documented.[4h]Herein we report the synthesis of crystalline, mesoporous TiO 2 beads with surface areas up to 108.0 m 2 g À1 and tunable pore sizes (pore diameters varying from 14.0 to 22.6 nm) through a facile combination of sol-gel and solvothermal processes. The mesoporous TiO 2 beads have a diameter of (830 AE 40) nm and are composed of anatase TiO 2 nanocrystals. These mesoporous TiO 2 beads have been used in the preparation of the working electrodes for DSSCs and an improved efficiency was observed when compared to cells prepared using standard Degussa P25 TiO 2 electrodes of similar thickness. An overall light conversion efficiency of 7.20% (open-circuit voltage (V oc ) of 777 mV, short-circuit current density (I sc ) of 12.79 mA cm À2 and fill factor (FF) of 0.72) was achieved using the mesoporous TiO 2 bead electrodes. Figure 1 shows scanning electron microscopy (SEM) images of the sol-gel prepared precursor materials and the calcined mesoporous TiO 2 beads prepared after t...

Perovskite solar cells (PSCs) have reached an impressive efficiency over 23%. One of its promising characteristics is the low-cost solution printability, especially for flexible solar cells. However, printing large area uniform electron transport layers on rough and soft plastic substrates without hysteresis is still a great challenge. Herein, we demonstrate slot-die printed high quality tin oxide films for high efficiency flexible PSCs. The inherent hysteresis induced by the tin oxide layer is suppressed using a universal potassium interfacial passivation strategy regardless of fabricating methods. Results show that the potassium cations, not the anions, facilitate the growth of perovskite grains, passivate the interface, and contribute to the enhanced efficiency and stability. The small size flexible PSCs achieve a high efficiency of 17.18% and large size (5 × 6 cm2) flexible modules obtain an efficiency over 15%. This passivation strategy has shown great promise for pursuing high performance large area flexible PSCs.

The hot-phonon bottleneck effect in lead-halide perovskites (APbX3) prolongs the cooling period of hot charge carriers, an effect that could be used in the next-generation photovoltaics devices. Using ultrafast optical characterization and first-principle calculations, four kinds of lead-halide perovskites (A=FA+/MA+/Cs+, X=I−/Br−) are compared in this study to reveal the carrier-phonon dynamics within. Here we show a stronger phonon bottleneck effect in hybrid perovskites than in their inorganic counterparts. Compared with the caesium-based system, a 10 times slower carrier-phonon relaxation rate is observed in FAPbI3. The up-conversion of low-energy phonons is proposed to be responsible for the bottleneck effect. The presence of organic cations introduces overlapping phonon branches and facilitates the up-transition of low-energy modes. The blocking of phonon propagation associated with an ultralow thermal conductivity of the material also increases the overall up-conversion efficiency. This result also suggests a new and general method for achieving long-lived hot carriers in materials.