Enhanced photovoltaic performance with co-sensitization of a ruthenium(ii) sensitizer and an organic dye in dye-sensitized solar cells

Co-sensitization is demonstrated to be an effective technique to enhance the efficiency of dye-sensitized solar cells, where an efficiency of 9.23% is achieved by mixing N3 and RK-1 dyes. The assembled solar cells are characterized by UV-vis absorption measurements, current-voltage characteristics, and electrochemical impedance spectroscopy. The co-sensitized solar cell shows an enhanced photovoltaic performance as compared to the devices sensitized by individual dyes. Upon optimization, the device made of 0.3 mM N3 + 0.2 mM RK-1 yielded Jsc = 18.1 mA cm2, Voc = 888 mV, FF = 57.44, and ? = 9.23%. This performance is superior to that of solar cells sensitized with either N3 (6.10%) or RK-1 (5.82%) fabricated under the same conditions. The enhanced efficiency can be attributed to the decrease of the competitive light absorption by I-/I3-, dye aggregation, and charge recombination. The Royal Society of Chemistry 2016.Scopu

Analysis of Photocarrier Dynamics at Interfaces in Perovskite Solar Cells by Time-Resolved Photoluminescence

The power conversion efficiency of perovskite solar cells is drastically affected by photocarrier dynamics at the interfaces. Experimental measurements show quenching of the photoluminescence (PL) signal from the perovskite layer when it is capped with a hole transport medium (HTM). Furthermore, time-resolved PL (TRPL) data show a faster decay of the PL signal in the presence of the perovskite/HTM interface. The experimental decay is usually fitted using one or two exponential functions with an incomplete physical picture. In this work, an extensive model is used to extract the key physical parameters characterizing carrier dynamics in the bulk and at the interfaces. The decay of the TRPL signal is calculated in the presence of both defect-assisted recombination (Shockley Read Hall) and band-to-band radiative recombination where carrier extraction/recombination at the interfaces is described by interface recombination velocities. By proper curve fitting of the modeling results and the measured TRPL signal, meaningful optoelectronic parameters governing photophysical processes in mixed halide perovskite thin films and single crystals are extracted. Furthermore, a sensitivity analysis to assess the contribution of these parameters on TRPL kinetics is also performed. Notably, the inclusion of the diffusion and surface recombination velocity at the interfaces allows to obtain the important physical parameters that govern the TRPL kinetics and improve the conformity of fits to experiments

CuSCN as Hole Transport Material with 3D/2D Perovskite Solar Cells

We report stable perovskite solar cells having 3D/2D perovskite absorber layers and CuSCN as an inorganic hole transporting material (HTM). (Phenylethyl)ammonium (PEA) and [(4-fluorophenyl)ethyl]ammonium (FPEA) have been chosen as 2D cations, creating thin layers of (PEA)(2)PbI4 or (FPEA)(2)PbI4 on top of the 3D perovskite. The 2D perovskite as an interfacial layer, neutralizes defects at the surface of the 3D perovskite absorber, and can protect from moistureinduced degradations. We demonstrate excellent charge extraction through the modified interfaces into the inorganic CuSCN HTM, with device efficiencies above 18%, compared to 19.3% with conventional spiro-OMeTAD. Furthermore, we show significantly enhanced ambient stability

Searching for Photoactive Polymorphs of CsNbQ₃ (Q = O, S, Se, Te) with Enhanced Optical Properties and Intrinsic Thermodynamic Stabilities

Nowadays, materials design efforts to obtain nontoxic and cost-effective photoactive semiconductors with a given chemical composition face the challenge of the coexistence of more than one configuration or crystal structure, so-called polymorphism. Polymorphs for multicomponent materials might exhibit various crystal structures by unique connectivity modes, hence creating polyhedral networks extended across the three-dimensional space or restricted along specific directions. A key component in photoactive materials design consists in the assessment of the thermodynamic stability of the various polymorphs along with their targeted properties, such as the optical band gap and the photon absorption efficiency. In this work, we conduct density functional theory calculations on cesium-niobate and cesium-niobium-chalcogenide CsNbO_3–<i>x</i>Q<i>_x</i> (Q = S, Se, Te, and <i>x</i> = 0, 1, 2, 3) compounds aiming at identifying intrinsically stable polymorphs with a high ability to absorb visible light. The connectivity between niobium-cation-centered polyhedra in the different polymorphs favors low dimensionality due to the large radius of the Cs cation. We identify unreported compounds, CsNbS₃ and CsNbSe₃, in the orthorhombic phase, where the polyhedra compose networks of low-dimensional connectivity as thermodynamically stable and strong visible-light absorbers

Intrinsic stability enhancement and ionic migration reduction by fluorinated cations incorporated in hybrid lead halide perovskites

Improving the stability of hybrid perovskite solar cells is believed to be the main step toward large scale commercialization of this technology. In this work, we demonstrate that the stability can be enhanced significantly by proper fluorination of the methylammonium cation. A systematic study to identify the optimal stability of the perovskite material with low controlled concentrations of modified cations was conducted using density functional theory (DFT). Our results suggest a route to enhance the thermodynamic stability of hybrid inorganic–organic perovskites, while at the same time reduce the ionic diffusion. The optimal fluorination has no significant impact on the band gap or the volume expansion of the CH3NH3PbI3 perovskite. We demonstrate that the fluorination has a tendency to stabilize the material due to the strengthening of some initially weak hydrogen bonds between MA+ cations and the surrounding lead-iodide framework. The observed strengthening is the result of internal structural deformations which are related to the formation of long C–N bonds. Finally, we showed through calculation that fluorination should reduce significantly the iodine vacancy mediated diffusion in the perovskite under applied bias voltage

Kirkendall Effect vs Corrosion of Silver Nanocrystals by Atomic Oxygen: From Solid Metal Silver to Nanoporous Silver Oxide

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