Efficient photocatalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Here we show that the effectiveness of each process can be separately maximized in a nanostructured heterojunction with extremely thin absorber layer. We demonstrate this concept on WO3/BiVO4+CoPi core-shell nanostructured photoanode that achieves near theoretical water splitting efficiency. BiVO4 is characterized by a high recombination rate of photogenerated carriers that have much shorter diffusion length than the thickness required for sufficient light absorption. This issue can be resolved by the combination of BiVO4 with more conductive WO3 nanorods in a form of core-shell heterojunction, where the BiVO4 absorber layer is thinner than the carrier diffusion length while it’s optical thickness is reestablished by light trapping in high aspect ratio nanostructures. Our photoanode demonstrates ultimate water splitting photocurrent of 6.72 mA cm−2 under 1 sun illumination at 1.23 VRHE that corresponds to ~90% of the theoretically possible value for BiVO4. We also demonstrate a self-biased operation of the photoanode in tandem with a double-junction GaAs/InGaAsP photovoltaic cell with stable water splitting photocurrent of 6.56 mA cm−2 that corresponds to the solar to hydrogen generation efficiency of 8.1%.

Hybrid CPbX 3 (C:C s, CH 3 NH 3 ;X :B r, I) perovskites possess excellent photovoltaic properties but are highly toxic, which hinders their practical application. Unfortunately,a ll Pb-free alternatives based on Sn and Ge are extremely unstable. Although stable and non-toxic C 2 ABX 6 double perovskites based on alternating corner-shared AX 6 and BX 6 octahedra (A = Ag, Cu;B = Bi, Sb) are possible, they have indirect and wide band gaps of over 2eV. However,i si tn ecessary to keep the corner-shared perovskite structure to retain good photovoltaic properties? Here, we demonstrate another family of photovoltaic halides based on edge-shared AX 6 and BX 6 octahedra with the general formula A a B b X x (x = a + 3 b)s uch as Ag 3 BiI 6 ,A g 2 BiI 5 ,A gBiI 4 , AgBi 2 I 7 .A sp erovskites were named after their prototype oxide CaTiO 3 discovered by Lev Perovski, we propose to name these new ABX halidesa sr udorffitesa fter Walter Rüdorff,w ho discoveredt heir prototype oxide NaVO 2 .W es tudied structural and optoelectronic properties of severalh ighly stable and promising Ag-Bi-I photovoltaic rudorffites that feature direct band gaps in the range of 1.79- Photovoltaic (PV) hybrid lead halide perovskites were first reported by Kojimae tal. [1] in 2006 with power conversion efficiency (PCE) of 2.2 %i nadye-sensitized solarc ell (DSSC) device configuration. However,t hese materials gained considerable attention only 6years later after two incremental improvements of their PCE to 3.8 %b yK ojimae tal. [2] and to 6.2 %b yI me tal. [3] Substitution of the liquid electrolyte with an efficient polymer hole-extraction layer by Lee et al. [4] in 2012 increased PCE to 10.9 %and was the turning point in perovskite photovoltaics that openedaway towardh ighly efficient and stable perovskite PV devices.S ince 2012 many researchers, mainly from the dye-sensitized and organic PV fields, joined the exciting research on perovskite solar cells. As ar esult, the PCE of the perovskite solarc ells showed as teep sigmoidal growth thatl ed to the contemporary efficiency of over 22 %. [5] Although this PCE is on par with other highly efficient thin-film PV technologies based on cadmium telluride (CdTe) and copper-indium-gallium selenide (CIGS), lead halide perovskites have the significant advantage of being solution processable, whicho fferss ubstantial cost reduction. Unfortunately,t he relianceo nh ighly toxic Pb hinders the commercial potentialo ft his technology. The toxicity of Pb is very high. The 50 %l ethal dose of lead [LD 50 (Pb)] is less than 5mgp er kg of body weight. In contrast to CdTe, which has excellent stability and negligible solubility in water with as olubility constant of K SP = 10 À34 ,P b-based halide perovskites can easily degrade and Pb can escape from ab roken PV module owing to the moderate solubility of PbI 2 (K SP = 4.4 10 À9 ). Despite various attempts to quantify the impact of potential pollution andi ntroduce life-cycle business modelst hat include integrity monitoring and recycling of perovskite PV modules, ...

Nanostructured photoanodes based on well-separated and vertically oriented WO3 nanorods capped with extremely thin BiVO4 absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO3 -NRs/BiVO4 photoanode modified with Co-Pi oxygen evolution co-catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm(2) at 1.23 V versus a reversible hydrogen electrode in a stable Na2 SO4 electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO4 layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO3 -NRs/BiVO4 photoanode effectively increases the optical thickness of the BiVO4 layer and results in efficient absorption of the incident light.

No abstract

Silicon nanocrystals (Si-ncs) with quantum confinement properties represent an attractive photovoltaic material. The ability to collect the photogenerated current through efficient electronic transport and exciton dissociation is a current challenge for the deployment of Si-nc based solar cells. We report here on prospective and cost-effective approaches to engineer the surface of electrochemically etched Si-ncs by laser fragmentation in ethanol and water. The properties of the engineered Si-ncs have been analyzed in detail by photoluminescence and absorption measurements together with Fourier transform infrared spectroscopy. To demonstrate the advantageous attributes of Si-nc surface engineering in liquid media, a few photovoltaic devices based on different architectures have been fabricated. First, anatase TiO2 nanotubes have been used as a host template for laser-fragmented Si-ncs to form inorganic-sensitized solar cell architectures. Second, we have produced bulk-heterojunction solar cells with a Si-nc/fullerene photoactive interface. This design has been further improved by functionalizing the Si-nc surface with water-soluble poly(3,4-ethylenedioxythiophene), i.e., PEDOT. All the devices produced here have been characterized with external quantum efficiency measurements, and in some cases the current−voltage characteristic has been also measured.