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The recent surge in efficiency and progress of organohalide perovskite solar cells (PSCs) has been significant. The PSC performance is significantly influenced by nanostructuring as this varies the intrinsic optical, electrical, and electrochemical properties. Diverse TiO2 electron transport layers (ETLs) are solvothermally grown on the transparent conducting oxide substrate with different dimensionalities, 0D nanoparticles (TNP), 1D nanowires (TNW) to 2D nanosheets (TNS), by varying the organic solvent used. These layers feature enhanced optical transparency (≈2%-5% transmittance improvement compared to pristine fluorine doped tin oxide, FTO, glass) minimizing light absorption losses. PSCs constructed using 1D TNW or 2D TNS yield enhanced photovoltaic performance compared to the 0D TNP counterparts. This is a result of i) improved infiltration of the perovskite in the porous TNW or TNS network and ii) facilitated electron transport and charge extraction at the TNW/perovskite or TNS/perovskite interfaces, thus reduced interfacial recombination loss. Employing a bilayered ETL film consisting of a selfassembled TiO2 blocking layer and a subsequent TNW active layer, produces PSC devices with an efficiency exceeding 16%. This bilayered ETL film can simultaneously block the photogenerated holes and enhance electron extraction, therefore improving PSC performance. [ABSTRACT FROM AUTHOR]

The microstructure of solution-processed organometallic lead halide perovskite thin films prepared by the 'gas-assisted' method is investigated with synchrotron-based techniques. Using a combination of GIWAXS and NEXAFS spectroscopy the orientational alignment of CH3NH3PbI3 crystallites and CH3NH3+ cations are separately probed. The GIWAXS results reveal a lack of preferential orientation of CH3NH3PbI3 crystallites in 200-250 nm thick films prepared on both planar TiO2 and mesoporous TiO2. Relatively high efficiencies are observed for device based on such films, with 14.3% achieved for planar devices and 12% for mesoporous devices suggesting that highly oriented crystallites are not crucial for good cell performance. Oriented crystallites however are observed in thinner films (≈60 nm) deposited on planar TiO2 (but not on mesoporous TiO2) indicating that the formation of oriented crystallites is sensitive to the kinetics of solvent evaporation and the underlying TiO2 morphology. NEXAFS measurements on all samples found that CH3NH3+ cations exhibit a random molecular orientation with respect to the substrate. The lack of any NEXAFS dichroism for the thin CH3NH3PbI3 layer deposited on planar TiO2 in particular indicates the absence of any preferential orientation of CH3NH3+ cations within the CH3NH3PbI3 unit cell for as-prepared layers, that is, without any electrical poling. [ABSTRACT FROM AUTHOR]

To achieve high-performance perovskite solar cells, especially with mesoscopic cell structure, the design of the electron transport layer (ETL) is of paramount importance. Highly branched anatase TiO2 nanowires (ATNWs) with varied orientation are grown via a facile one-step hydrothermal process on a transparent conducting oxide substrate. These films show good coverage with optimization obtained by controlling the hydrothermal reaction time. A homogeneous methyl­ammonium lead iodide (CH3NH3PbI3) perovskite thin film is deposited onto these ATNW films forming a bilayer architecture comprising of a CH3NH3PbI3 sensitized ATNW bottom layer and a CH3NH3PbI3 capping layer. The formation, grain size, and uniformity of the perovskite crystals strongly depend on the degree of surface coverage and the thickness of the ATNW film. Solar cells constructed using the optimized ATNW thin films (220 nm in thickness) yield power conversion efficiencies up to 14.2% with a short-circuit photocurrent density of 20.32 mA cm−2, an open-circuit photovoltage of 993 mV, and a fill factor of 0.70. The dendritic ETL and additional perovskite capping layer efficiently capture light and thus exhibit a superior light harvesting efficiency. The ATNW film is an effective hole-blocking layer and efficient electron transport medium for excellent charge separation and collection within the cells. [ABSTRACT FROM AUTHOR]

Nanostructured porous tin-doped indium oxide (ITO) films were prepared by screen printing of an ITO nanoparticle paste onto conducting fluorine-doped tin oxide (FTO) substrates. The ITO films were subsequently coated with thin layers of TiO 2 by the hydrolysis of TiCl 4 to form the collector–shell photoelectrodes. The morphology of films was analysed by scanning electron microscope (SEM). It was found that a uniform coating of TiO 2 was achieved when three or more deposition cycles were applied. Dye-sensitized solar cells were constructed with the collector–shell photoelectrodes using an electrolyte containing the [Co(bpy) 3 ] 2+/3+ (bpy = 2,2′-bipyridine) redox couple and MK-2, an organic sensitizer and efficiencies of 3.3% achieved. Charge transport in cells utilizing the collector–shell electrodes was found to be 2–6 times faster than those utilizing P25-based TiO 2 electrodes. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]