Luis G. Gerling

Bio: Luis G. Gerling is an academic researcher from Polytechnic University of Catalonia. The author has contributed to research in topics: Solar cell & Crystalline silicon. The author has an hindex of 15, co-authored 23 publications receiving 892 citations. Previous affiliations of Luis G. Gerling include ICFO – The Institute of Photonic Sciences.

Origin of passivation in hole-selective transition metal oxides for crystalline silicon heterojunction solar cells

Abstract: Transition metal oxides (TMOs) have recently demonstrated to be a good alternative to boron/phosphorous doped layers in crystalline silicon heterojunction solar cells. In this work, the interface between n-type c-Si (n-Si) and three thermally evaporated TMOs (MoO3, WO3, and V2O5) was investigated by transmission electron microscopy, secondary ion-mass, and x-ray photoelectron spectroscopy. For the oxides studied, surface passivation of n-Si was attributed to an ultra-thin (1.9–2.8 nm) SiOx ∼1.5 interlayer formed by chemical reaction, leaving oxygen-deficient species (MoO, WO2, and VO2) as by-products. Carrier selectivity was also inferred from the inversion layer induced on the n-Si surface, a result of Fermi level alignment between two materials with dissimilar electrochemical potentials (work function difference Δϕ ≥ 1 eV). Therefore, the hole-selective and passivating functionality of these TMOs, in addition to their ambient temperature processing, could prove an effective means to lower the cost and simplify solar cell processing.

A prototype reactor for highly selective solar-driven CO2 reduction to synthesis gas using nanosized earth-abundant catalysts and silicon photovoltaics

Abstract: The conversion of carbon dioxide (CO2) into value-added chemicals and fuels, preferably using renewable energy and earth-abundant materials, is considered a key priority for future energy research. In this work, a bias-free reactor device for the solar-driven conversion of CO2 to synthesis gas (syngas) has been developed. The integrated fluidic device consists of a cathode made of copper foam coated with low-cost nanosized zinc flakes as catalyst to perform the CO2 reduction reaction (CO2RR) to syngas, an adapted silicon heterojunction solar cell structure as photoanode with nickel foam as catalyst to facilitate the oxygen evolution reaction (OER), and a bipolar membrane separating the respective catholyte and anolyte compartments. The membrane allows for the operation of the catholyte and anolyte at different pH values. Stable and tunable hydrogen-to-carbon monoxide (H2 : CO) ratios between 5 and 0.5 along with high CO Faradaic efficiencies of up to 85% and CO current densities of 39.4 mA cm−2 have been demonstrated. Under photoelectrolysis conditions, the photovoltage of the photoanode was varied between 0.6 V and 2.4 V by connecting up to four heterojunction solar cells in series, and thus reducing the overall cell voltage solely by solar energy utilization. Bias-free operation of the integrated device has been achieved under ambient conditions with active areas for CO2RR and OER, respectively, of 10 cm2. An operation current density of 5.0 mA cm−2 was measured under 100 mW cm−2 illumination of the complete device, which corresponds to a solar-to-syngas conversion efficiency of 4.3%.

V2Ox-based hole-selective contacts for c-Si interdigitated back-contacted solar cells

Abstract: Over the last few years, transition metal oxide layers have been proposed as selective contacts both for electrons and holes and successfully applied to silicon solar cells. However, better published results need the use of both a thin and high quality intrinsic amorphous Si layer and TCO (Transparent Conductive Oxide) films. In this work, we explore the use of vanadium suboxide (V2Ox) capped with a thin Ni layer as a hole transport layer trying to avoid both the intrinsic amorphous silicon layer and the TCO contact layer. Obtained figures of merit for Ni/V2Ox/c-Si(n) test samples are saturation current densities of 175 fA cm−2 and specific contact resistance below 115 mΩ cm2 on 40 nm thick V2Ox layers. Finally, the Ni/V2Ox stack is used with an interdigitated back-contacted c-Si(n) solar cell architecture fully fabricated at low temperatures. An open circuit voltage, a short circuit current and a fill factor of 656 mV, 40.7 mA cm−2 and 74.0% are achieved, respectively, leading to a power conversion efficiency of 19.7%. These results confirm the high potential of Ni/V2Ox stacks as hole-selective contacts on crystalline silicon photovoltaics.

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels.

Abstract: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metal-free, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

Missing-linker metal-organic frameworks for oxygen evolution reaction.

Abstract: Metal-organic frameworks (MOFs) have been recognized as compelling platforms for the development of miscellaneous applications because of their structural diversity and functional tunability. Here, we propose that the electrocatalytic properties could be well modified by incorporating missing linkers into the MOF. Theoretical calculations suggest the electronic structure of MOFs can be tuned by introducing missing linkers, which improves oxygen evolution reaction (OER) performance of the MOF. Inspired by these aspects, we introduced various missing linkers into a layered-pillared MOF Co2(OH)2(C8H4O4) (termed as CoBDC) to prepare missing-linker MOFs. Transmission electron microscope and synchrotron X-ray measurements confirmed that the missing linkers in the MOF could be introduced and well controlled by our strategy. The self-supported MOF nanoarrays with missing linkers of carboxyferrocene exhibit excellent OER performance with ultralow overpotential of 241 mV at 100 mA cm−2. This work opens a new prospect to develop efficient MOF-based electrocatalysts by introducing missing linkers. While water splitting electrocatalysis provides a means to store electrical energy as fuel, the water oxidation catalysts typically show low performances. Here, authors employ metal-organic frameworks with missing-linkers as highly active oxygen evolution electrocatalysts.

Passivating contacts for crystalline silicon solar cells

Abstract: The global photovoltaic (PV) market is dominated by crystalline silicon (c-Si) based technologies with heavily doped, directly metallized contacts. Recombination of photo-generated electrons and holes at the contact regions is increasingly constraining the power conversion efficiencies of these devices as other performance-limiting energy losses are overcome. To move forward, c-Si PV technologies must implement alternative contacting approaches. Passivating contacts, which incorporate thin films within the contact structure that simultaneously supress recombination and promote charge-carrier selectivity, are a promising next step for the mainstream c-Si PV industry. In this work, we review the fundamental physical processes governing contact formation in c-Si. In doing so we identify the role passivating contacts play in increasing c-Si solar cell efficiencies beyond the limitations imposed by heavy doping and direct metallization. Strategies towards the implementation of passivating contacts in industrial environments are discussed. The development of passivating contacts holds great potential for enhancing the power conversion efficiency of silicon photovoltaics. Here, De Wolf et al. review recent advances in material design and device architecture, and discuss technical challenges to industrial fabrication.

Two-dimensional-related catalytic materials for solar-driven conversion of COx into valuable chemical feedstocks.

Abstract: The discovery of improved chemical processes for CO and CO2 hydrogenation to valuable hydrocarbon fuels and alcohols is of paramount importance for the chemical industry. Such technologies have the potential to reduce anthropogenic CO2 emissions by adding value to a waste stream, whilst also reducing our consumption of fossil fuels. Current thermal catalytic technologies available for CO and CO2 hydrogenation are demanding in terms of energy input. Various alternative technologies are now being developed for COx hydrogenation, with solar-driven processes over two-dimensional (2D) and 2D-related composite materials being particularly attractive due to the abundance of solar energy on Earth and also the high selectivity of defect-engineered 2D materials towards specific valuable products under very mild reaction conditions. This review showcases recent advances in the solar-driven COx reduction to hydrocarbons over 2D-based materials. Optimization of 2D catalyst performance demands interdisciplinary research that embraces catalyst electronic structure manipulation and morphology control, surface/interface engineering, reactor engineering and density functional theory modelling studies. Through improved understanding of the structure–performance relationships in 2D-related catalysts which is achievable through the application of modern in situ characterization techniques, practical photo/photothermal/photoelectrochemical technologies for CO and CO2 reduction to high-valuable products such as olefins could be realized in the not-too-distant future.

Efficient electrically powered CO2-to-ethanol via suppression of deoxygenation

Abstract: The carbon dioxide electroreduction reaction (CO2RR) provides ways to produce ethanol but its Faradaic efficiency could be further improved, especially in CO2RR studies reported at a total current density exceeding 10 mA cm−2. Here we report a class of catalysts that achieve an ethanol Faradaic efficiency of (52 ± 1)% and an ethanol cathodic energy efficiency of 31%. We exploit the fact that suppression of the deoxygenation of the intermediate HOCCH* to ethylene promotes ethanol production, and hence that confinement using capping layers having strong electron-donating ability on active catalysts promotes C–C coupling and increases the reaction energy of HOCCH* deoxygenation. Thus, we have developed an electrocatalyst with confined reaction volume by coating Cu catalysts with nitrogen-doped carbon. Spectroscopy suggests that the strong electron-donating ability and confinement of the nitrogen-doped carbon layers leads to the observed pronounced selectivity towards ethanol. The electroreduction of CO2 to ethanol could enable the clean production of fuels using renewable power. This study shows how confinement effects from nitrogen-doped carbon layers on copper catalysts enable selective ethanol production from CO2 with a Faradaic efficiency of up to 52%.