Kunwu Fu

Laminated Carbon Nanotube Networks for Metal Electrode-Free Efficient Perovskite Solar Cells

Organic-inorganic metal halide perovskite solar cells were fabricated by laminating films of a carbon nanotube (CNT) network onto a CH3NH3PbI3 substrate as a hole collector, bypassing the energy-consuming vacuum process of metal deposition. In the absence of an organic hole-transporting material and metal contact, CH3NH3PbI3 and CNTs formed a solar cell with an efficiency of up to 6.87%. The CH3NH3PbI3/CNTs solar cells were semitransparent and showed photovoltaic output with dual side illuminations due to the transparency of the CNT electrode. Adding spiro-OMeTAD to the CNT network forms a composite electrode that improved the efficiency to 9.90% due to the enhanced hole extraction and reduced recombination in solar cells. The interfacial charge transfer and transport in solar cells were investigated through photoluminescence and impedance measurements. The flexible and transparent CNT network film shows great potential for realizing flexible and semitransparent perovskite solar cells.

A simple spiro-type hole transporting material for efficient perovskite solar cells

We developed a cost-effective spiro-type 4,4′,4′′,4′′′\-(2H,2′H,4H,4′H-3,3′-spiro-bi[thieno[3,4-b][1,4]dioxepine]-6,6′,8,8′-tetrayl)tetrakis(N,N-bis(4-methoxyphenyl)aniline) hole transporting material (PST1) for perovskite solar cells (PSCs) that works efficiently even without a cobalt dopant. The PST1 is obtained by employing facile synthetic routes and tends to crystallize in the solid state. An X-ray diffraction study of PST1 revealed a unique quasi-spiro molecular configuration and found multiple CH/π and π–π intermolecular contacts. For the first time, the crystal structure of 2,2′,7,7′-tetrakis(N,N′-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-OMeTAD) is also studied for comparison. The device based on PST1 exhibited a PCE of 13.44%, and a comparable 12.74% PCE was achieved for its undoped form, which paves the way for developing new low cost hole transporting materials and final industrialization of perovskite solar cells.

Silicon decorated with amorphous cobalt molybdenum sulfide catalyst as an efficient photocathode for solar hydrogen generation.

The construction of viable photoelectrochemical (PEC) devices for solar-driven water splitting can be achieved by first identifying an efficient independent photoanode for water oxidation and a photocathode for hydrogen generation. These two photoelectrodes then must be assembled with a proton exchange membrane within a complete coupled system. Here we report the preparation of a Si/a-CoMoSx hybrid photocathode which shows impressive performance (onset potential of 0.25 V vs RHE and photocurrent jsc of 17.5 mA cm(-2) at 0 V vs RHE) in pH 4.25 phosphate solution and under simulated AM 1.5 solar illumination. This performance is among the best reported for Si photocathodes decorated with noble-metal-free catalysts. The electrode preparation is scalable because it relies on a photoassisted electrodeposition process employing an available p-type Si electrode and [Co(MoS4)2](2-) precursor. Investigation of the mechanism of the Si/a-CoMoSx electrode revealed that under conditions of H2 photogeneration this bimetallic sulfide catalyst is highly efficient in extracting electrons from illuminated Si and subsequently in reducing protons into H2. The Si/a-CoMoSx photocathode is functional over a wide range of pH values, thus making it a promising candidate for the construction of a complete solar-driven water splitting PEC device.

MODULATING CH3NH3PbI3 PEROVSKITE CRYSTALLIZATION BEHAVIOR THROUGH PRECURSOR CONCENTRATION

Perovskite-based photovoltaic devices have recently achieved impressively high efficiencies beyond 15% and gained great interest. We show here the formation of perovskite cluster overlayer structures which consist of individual perovskite grains on top of mesoporous TiO2 films, coexisting with the randomly distributed nanocrystals within the films. Perovskite solution concentration was found to play an important role in modulating the perovskite crystallization and cluster overlayer formation process. Absorbance increase in visible wavelength range and shift of photoluminescence (PL) responses of perovskite films due to the effect of precursor concentration change were observed and investigated in detail. The crystallographic analysis of the CH3NH3PbI3 films shows a gradual decrease of the perovskite lattice parameters and shrinkage of unit volume as precursor solution concentration increases, which is correlated to the changes of optical properties. Finally, perovskite-based solar cell device performance was enhanced at higher precursor concentration.

Modelling and loss analysis of meso-structured perovskite solar cells

A mathematical model for meso-structured perovskite solar cells is derived and calibrated towards measured intensity dependent current-voltage characteristics. This steady-state device model describes the transport of free carriers, carrier recombination and optical generation. The optical part considers internal transmission, reflection, and absorption of light, using a transfer matrix approach. The carrier recombination in the form of radiative, Auger and Shockley-Read-Hall mechanisms is accounted for inside the perovskite capping layer, as well as interfacial recombination between the perovskite and electron/hole-transporting layers. After calibration by best-fitting the unknown parameters towards intensity dependent current-voltage measurements of an in-house fabricated meso-structured perovskite solar cell, we identify the dominant recombination mechanisms and their locations inside the cell. A subsequent loss analysis indicates that, in our fabricated solar cell, the interfacial recombination betwee...