Efficient and stable perovskite solar cells with a simple active layer are desirable for manufacturing. Three-dimensional perovskite solar cells are most efficient but need to have improved environmental stability. Inclusion of larger ammonium salts has led to a trade-off between improved stability and efficiency, which is attributed to the perovskite films containing a two-dimensional component. Here, we show that addition of 0.3 mole percent of a fluorinated lead salt into the three-dimensional methylammonium lead iodide perovskite enables low temperature fabrication of simple inverted solar cells with a maximum power conversion efficiency of 21.1%. The perovskite layer has no detectable two-dimensional component at salt concentrations of up to 5 mole percent. The high concentration of fluorinated material found at the film-air interface provides greater hydrophobicity, increased size and orientation of the surface perovskite crystals, and unencapsulated devices with increased stability to high humidity.

Infrared (IR) light represents an untapped energy source accounting for almost half of all solar energy. Thus, there is a need to develop systems to convert IR light to fuel and make full use of this plentiful resource. Herein, we report photocatalytic H 2 evolution driven by near-to shortwave-IR light (up to 2500 nm) irradiation, based on novel CdS/Cu 7 S 4 heterostructured nanocrystals. The apparent quantum yield reached 3.8% at 1100 nm, which exceeds the highest efficiencies achieved by IR light energy conversion systems reported to date. Spectroscopic results revealed that plasmon-induced hotelectron injection at p−n heterojunctions realizes exceptionally long-lived charge separation (>273 μs), which results in efficient IR light to hydrogen conversion. These results pave the way for the exploration of undeveloped low-energy light for solar fuel generation.

Metal-complex/semiconductor hybrids have attracted attention as photocatalysts for visible-light CO 2 reduction, and electron transfer from the metal complex to the semiconductor is critically important to improve the performance. Here rutile TiO 2 nanoparticles having 5−10 nm in size were employed as modifiers to improve interfacial charge transfer between semiconducting carbon nitride nanosheets (NS-C 3 N 4 ) and a supramolecular Ru(II)−Re(I) binuclear complex (RuRe). The RuRe/TiO 2 /NS-C 3 N 4 hybrid was capable of photocatalyzing CO 2 reduction into CO with high selectivity under visible light (λ > 400 nm), outperforming an analogue without TiO 2 by a factor of 4, in terms of both CO formation rate and turnover number (TON). The enhanced photocatalytic activity was attributed primarily to prolonged lifetime of free and/or shallowly trapped electrons generated in TiO 2 /NS-C 3 N 4 under visible-light irradiation, as revealed by transient absorption spectroscopy. Experimental results also indicated that the TiO 2 modifier served as a good adsorption site for RuRe, which resulted in the suppression of undesirable desorption of the complex, thereby contributing to the improved photocatalytic performance. This study presents the first successful example of interfacial manipulation in a metal-complex/semiconductor hybrid photocatalyst for improved visible-light CO 2 reduction to produce CO.

We have previously developed photocatalytic CO 2 reduction systems using graphitic carbon nitride (g-C 3 N 4 ) and a Ru(II) mononuclear complex (e.g., trans(Cl)− [Ru II {4,4′-(H 2 PO 3 ) 2 bpy} 2 (CO) 2 Cl 2 ] bpy = 2,2′-bipyridine, abbreviated as RuP) hybrids and demonstrated its high activities under visible light (λ > 400 nm). To understand the excited-state dynamics of C 3 N 4 and electron-transfer process to RuP, here we examined the photophysical properties of g-C 3 N 4 as well as mesoporous g-C 3 N 4 (mpg-C 3 N 4 ) by means of time-resolved emission and/or time-resolved infrared absorption (TR-IR) spectroscopy. The emission decay measurements showed that g-C 3 N 4 (as well as mpg-C 3 N 4 ) has at least three emissive excited states with different lifetimes (g-C 3 N 4 ; 1.3 ± 0.4, 3.9 ± 0.9, and 15 ± 4 ns at 269 nm photoexcitation) in aqueous suspension. These excited states were not quenched upon addition of a hole scavenger (e.g., disodium dihydrogen ethylenediamine tetraacetate dehydrate) and/or an electron acceptor (RuP), even though photochemical electron-transfer processes from/to g-C 3 N 4 has been experimentally confirmed by photocatalytic reactions. On the other hand, TR-IR spectroscopy clearly indicated that mobile electrons photogenerated in mpg-C 3 N 4 , which are shallowly trapped and/or free electron in the conduction band, are able to move into RuP with a timescale of a few picoseconds. These results suggest that main emission centers and reaction sites (including charge-transfer interfaces) are separately located in the C 3 N 4 materials, and that electron transfer from C 3 N 4 to RuP progresses through less-or non-luminescent sites, in which mobile electrons exist with a certain lifetime.

Promotional effect of Ag species on visible-light CO2 reduction by a Ru-complex/Ag/C3N4 photocatalyst was examined.