We report annealing-free compact TiOx layer by atomic layer deposition for high efficiency flexible perovskite solar cells, and maintained 95% of the initial PCE after 1000 bending cycles with 10 mm bending radius.

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Excellent color purity with a tunable band gap renders organic-inorganic halide perovskite highly capable of performing as light-emitting diodes (LEDs). Perovskite nanocrystals show a photoluminescence quantum yield exceeding 90%, which, however, decreases to lower than 20% upon formation of a thin film. The limited photoluminescence quantum yield of a perovskite thin film has been a formidable obstacle for development of highly efficient perovskite LEDs. Here, we report a method for highly luminescent MAPbBr (MA = CHNH) nanocrystals formed in situ in a thin film based on nonstoichiometric adduct and solvent-vacuum drying approaches. Excess MABr with respect to PbBr in precursor solution plays a critical role in inhibiting crystal growth of MAPbBr, thereby forming nanocrystals and creating type I band alignment with core MAPbBr by embedding MAPbBr nanocrystals in the unreacted wider band gap MABr. A solvent-vacuum drying process was developed to preserve nanocrystals in the film, which realizes a fast photoluminescence lifetime of 3.9 ns along with negligible trapping processes. Based on a highly luminescent nanocrystalline MAPbBr thin film, a highly efficient green LED with a maximum external quantum efficiency of 8.21% and a current efficiency of 34.46 cd/A was demonstrated.

We report on reduced graphene oxide (rGO)/mesoporous (mp)-TiO2 nanocomposite based mesostructured perovskite solar cells that show an improved electron transport property owing to the reduced interfacial resistance. The amount of rGO added to the TiO2 nanoparticles electron transport layer was optimized, and their impacts on film resistivity, electron diffusion, recombination time, and photovoltaic performance were investigated. The rGO/mp-TiO2 nanocomposite film reduces interfacial resistance when compared to the mp-TiO2 film, and hence, it improves charge collection efficiency. This effect significantly increases the short circuit current density and open circuit voltage. The rGO/mp-TiO2 nanocomposite film with an optimal rGO content of 0.4 vol % shows 18% higher photon conversion efficiency compared with the TiO2 nanoparticles based perovskite solar cells.

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MgO ultrathin nanolayers are able to efficiently retard charge recombination in perovskite solar cells.

Coupling dissimilar oxides in heterostructures allows the engineering of interfacial, optical, charge separation/transport and transfer properties of photoanodes for photoelectrochemical (PEC) water splitting. Here, we demonstrate a double-heterojunction concept based on a BiVO/WO/SnO triple-layer planar heterojunction (TPH) photoanode, which shows simultaneous improvements in the charge transport (∼93% at 1.23 V vs RHE) and transmittance at longer wavelengths (>500 nm). The TPH photoanode was prepared by a facile solution method: a porous SnO film was first deposited on a fluorine-doped tin oxide (FTO)/glass substrate followed by WO deposition, leading to the formation of a double layer of dense WO and a WO/SnO mixture at the bottom. Subsequently, a BiVO nanoparticle film was deposited by spin coating. Importantly, the WO/(WO+SnO) composite bottom layer forms a disordered heterojunction, enabling intimate contact, lower interfacial resistance, and efficient charge transport/transfer. In addition, the top BiVO/WO heterojunction layer improves light absorption and charge separation. The resultant TPH photoanode shows greatly improved internal quantum efficiency (∼80%) and PEC water oxidation performance (∼3.1 mA/cm at 1.23 V vs RHE) compared to the previously reported BiVO/WO photoanodes. The PEC performance was further improved by a reactive-ion etching treatment and CoO electrocatalyst deposition. Finally, we demonstrated a bias-free and stable solar water-splitting by constructing a tandem PEC device with a perovskite solar cell (STH ∼3.5%).

We describe the fabrication of crystallographically preferred oriented TiO 2 anatase nanotube arrays (p-NTAs) and the characterization of their photovoltaic properties. The preferred orientation to the (004) plane of the TiO 2 nanotube array (NTA) was carefully controlled by adjusting the water content in the anodizing electrolyte; $2 wt% of water yielded a p-NTA, whereas other contents of water yielded randomly oriented NTAs (r-NTAs). A structural analysis using X-ray diffraction and a high-resolution transmission electron microscope revealed that the p-NTA showed a preferred orientation along the [001] direction of the anatase crystal structure. When the NTAs were employed to dye-sensitized solar cells (DSSCs) as photoelectrodes, the p-NTA showed a similar electron lifetime to the r-NTA, which was an order of magnitude higher than that for a TiO 2 nanoparticle (NP) film. Moreover, the p-NTA exhibited faster electron transport than the NP film, and even faster than the r-NTA. These properties resulted in a longer electron diffusion length of the p-NTA, compared to the r-NTA and NP film, thereby improving the charge collection property of the photoelectrode. The p-NTA exhibited superior photovoltaic energy conversion performance in the DSSC system, and showed a higher thickness for the optimal photovoltaic performance compared to the NP film, which were attributed to the excellent charge collection properties. Our results address that the crystallographic orientation of NTAs improves their charge transport properties, which can be applied to various optoelectronics, especially to solar-driven energy conversion devices.