Neutral water splitting catalysis with a high FF triple junction polymer cell

This document is the Accepted Manuscript version of a Published Work that appeared in final form in CS catalysis, copyright © American Chemical Society, after peer review and technical editing by the publisher and may be found at http://dx.doi.org/10.1021/acscatal.6b01036We report a photovoltaics-electrochemical (PV-EC) assembly based on a compact and easily processable triple homojunction polymer cell with high fill factor (76%), optimized conversion efficiencies up to 8.7%, and enough potential for the energetically demanding water splitting reaction (V-oc = 2.1 V). A platinum-free cathode made of abundant materials is coupled to a ruthenium oxide on glassy carbon anode (GC-RuO2) to perform the reaction at optimum potential (Delta E = 1.70-1.78 V, overpotential = 470-550 mV). The GC-RuO2 anode contains a single monolayer of catalyst corresponding to a superficial concentration (Gamma) of 0.15 nmol cm(-2) and is highly active at pH 7. The PV-EC cell achieves solar to hydrogen conversion efficiencies (STH) ranging from 5.6 to 6.0%. As a result of the solar cell's high fill factor, the optimal photovoltaic response is found at 1.70 V, the minimum potential at which the electrodes used perform the water splitting reaction. This allows generating hydrogen at efficiencies that would be very similar (96%) to those obtained as if the system were to be operating at 1.23 V, the thermodynamic potential threshold for the water splitting reaction.Peer ReviewedPostprint (author's final draft

4‑Terminal Tandem Photovoltaic Cell Using Two Layers of PTB7:PC₇₁BM for Optimal Light Absorption

A 4-terminal architecture is proposed in which two thin active layers (<100 nm) of PTB7:PC₇₁BM are deposited on a two-sided ITO covered glass substrate. By modeling the electric field distribution inside the multilayer structure and applying an inverse solving problem procedure, we designed an optimal device architecture tailored to extract the highest photocurrent possible. By adopting such a 4-terminal configuration, we numerically demonstrated that even when the two subcells use identical absorber materials, the performance of the 4-terminal device may overcome the performance of the best equivalent single-junction device. In an experimental implementation of such a 4-terminal device, we demonstrate the viability of the approach and find a very good match with the trend of the numerical predictions

UV-Induced Oxygen Removal for Photostable, High-Efficiency PTB7-Th:PC₇₁BM Photovoltaic Cells

Solution-processed ZnO sol–gel or nanoparticles are widely used as the electron-transporting layer (ETL) in optoelectronic devices. However, chemisorbed oxygen on the ZnO layer surface has been shown to be detrimental for the device performance as well as stability. Herein, we demonstrate that chemisorbed oxygen removal based on UV illumination of the ZnO surface layer under a nitrogen atmosphere can, simultaneously, improve the power conversion efficiency and photostability of PTB7-Th:PC71BM-based inverted polymer solar cells. By a systematic study of such a UV illumination procedure, we obtained optimal conditions where both the cell efficiency and stability were improved. We fabricated cells with a power conversion efficiency higher than 9.8% and with a T80 lifetime longer than 500 h, corresponding to about a 2.5-fold enhancement relative to non-UV-treated ZnO reference devices

Novel composites for nonlinear optics

A fully computerised Temperature-Gradient Zone-Melting (TGZM) apparatus was designed and built in order to produce novel and highly aligned composite films for Second Harmonic Generation (SHG). The TGZM apparatus consists of hot and cold aluminium blocks with glass-ceramic thermal insulator sandwiched between the two blocks. The composite films contain SHG-active guest crystals incorporated within a polymer matrix (host) forming a guest/host structure. These composites exhibit good optical performance in terms of SHG output (guest crystal), high mechanical strength, thermal and chemical stability (host polymer). These particular properties are of great importance especially for fibre-optical applications. 3-methyl-4-methoxy-4'-nitrostilbene (MMONS) is SHG-active guest material which was investigated by incorporating it in poly(methyl methacrylate) or PMMA(host polymer). Two PMMA average molecular weights (AMW) were used once at a time, in which the effect of that on the overall SHG intensity was clearly observed. It was found that a change of a polymer AMW does alter the output of the SHG signal. MMONS crystals were also embedded in another polymer host called Polystyrene (PS) in order to demonstrate the effect of using two different polymers on the SHG intensity of MMONS aligned films. The samples were cast on a glass slides and placed on the hot side of the TGZM apparatus (crystal growth from melt). Later they were drawn towards the cold side with a drawing rate closely matching the MMONS crystal growth rate and producing highly aligned composite films. A Nd:YAG laser beam (1064 nm) with 10 mJ fundamental energy was incident on the above samples (45 deg. from the optic axis z) using type II phase matching, resulting in a green second harmonic signal of 532 nm. The refractive index mismatch between MMONS and a polymer host such as poly(9-vinyle carbazole) or PVK (used in this project) could cause a major light scattering (i.e light loss) during SHG intensity measurements, leading to very much reduced harmonic signal. In order to overcome this problem, a certain amounts of dye (9-methylanthracene, 9-MA) was added in order to modify the overall refractive index of MMONS/PVK in a process called refractive index matching. Higher SHG output was observed than the case where no dye was involved. The refractive index measurements of MMONS/[PVK/9-MA] aligned films were performed using the waveguide prism coupler method to identify the point of refractive index matching at which the aligned film acts as a single medium. As a result of this process, the angular distribution of light transmission (using He-Ne laser beam at 633 nm) was observed to be at its highest level when the refractive index matching point is reached. (author)SIGLEAvailable from British Library Document Supply Centre-DSC:DXN031266 / BLDSC - British Library Document Supply CentreGBUnited Kingdo