Aluminium induced texturing of glass substrates with improved light management for thin film solar cells

Aluminium induced texturing (AIT) method has been used to texture glass substrates to enhance photon absorption in microcrystalline thin film Si solar cells. In this process, a thin Al film is deposited on a glass substrate and a non-uniform redox reaction between the glass and the Al film occurs when they are annealed at high temperature. After etching the reaction products, the resultant glass surface presents a uniform and rough morphology. In this work, three different textures (­σrms ~85, ~95, ~125 nm) have been achieved by tuning the dc sputtering power and over them and over smooth glass, pin microcrystalline silicon solar cells have been fabricated. The cells deposited over the textured substrates showed an efficiency improvement in comparison to the cells deposited over the smooth glass. The best result was given for the glass texture σrms~125 nm that led to an average efficiency 2.1% higher than that given by the cell deposited on smooth glas

Light induced water splitting using multijunction thin film silicon solar cells

It has been widely recognised that fossil fuel reserves are not suffcient to cover the energy demand of our societies in the future, even if the energy utilisation would stagnate on today's level. The extent of the problem is also associated with the emission of the greenhouse gas CO$_{2}$ upon combustion of fossil fuels that can lead to unpredictable climate changes on earth. Nature's own processes of fuel generation based on biomass utilisation are considered to be not effcient enough to replenish the used resources on a short time scale. To relieve this predicament, a transition from fossil fuels to renewable energy sources is therefore imperative and unavoidable. Renewable and carbon-free energy from wind and solar radiation are the only means which can fully replace fossil fuels and are able to cover an increasing energy demand in the future. But up to now, these fluctuating energy resources lack an appropriate and effcient storage technology. Light induced water splitting, a process that mimics natural photosynthesis, provides a viable example of an ecofriendly energy concept as it converts solar energy into a storable and clean chemical fuel with a high gravimetric energy density, namely hydrogen. To be competitive with fossil fuels or hydrogen production by other means, this process must however become highly effcient and low-cost. In this regard, the utilisation of semiconductor based devices for the photoelectrochemical generation of hydrogen from water and sunlight is a promising and elegant means to store renewable energy and has been attracting considerable interest among research groups worldwide. To split water effciently into its components hydrogen and oxygen the semiconductor photoelectrode has to meet several requirements [...

Impact of Light-Induced Degradation on the Performance of Multijunction Thin-Film Silicon-Based Photoelectrochemical Water-Splitting Devices

The impact of light-induced degradation (LID) of silicon photoelectrodes on the solar-to-hydrogen efficiency of photoelectrochemical (PEC) devices is investigated. To evaluate the effect, stabilized state-of-the-art thin-film silicon solar cells (after 1000 h of light soaking) were used as photocathodes in photovoltaic–electrochemical (PV–EC) device assemblies and their performances were compared to the performances of the initial solar-cell-based PV–EC devices. A wide range of photoelectrode configurations (tandem, triple, quadruple) was addressed. With regard to the widespread use of multijunction-based photoelectrodes in the literature, the results presented herein will have a high impact and may serve as guidelines for the design of photovoltaic devices particularly tailored for PEC applications, with high stabilities and efficiencies. It is shown that LID affects the performances of PV and PV–EC devices in different ways and strongly depends on the photovoltage of the applied solar cell

Photoelectrochemical Water Splitting using Adapted Silicon Based Multi-Junction Solar Cell Structures: Development of Solar Cells and Catalysts, Upscaling of Combined Photovoltaic-Electrochemical Devices and Performance Stability

Thin film silicon based multi-junction solar cells were developed for application in combined photovoltaic electrochemical systems for hydrogen production from water splitting. Going from single, tandem, triple up to quadruple junctions, we cover a range of open circuit voltages from 0.5 V to 2.8 V at photovoltaic cell (PV) efficiencies above 13%. The solar cells were combined with electrochemical (EC) cells in integrated devices from 0.5 cm2 to 64 cm2. Various combinations of catalyst pairs for the oxygen and hydrogen evolution reaction side (OER and HER) were investigated with respect to electrochemical activity, stability, cost and – important for the integrated device – optical quality of the metal catalyst on the HER side as back reflector of the attached solar cell. The combined PV-EC systems were further investigated under varied operation temperatures and illumination conditions for estimation of outdoor performance and annual fuel production yield. For 0.5 cm2 size combined systems a maximum solar-to-hydrogen efficiency ηSTH = 9.5% was achieved under standard test conditions. For device upscaling to 64 cm2 various concepts of contact interconnects for reduced current and fill factor loss when using large size solar cells were investigated. To replace high performance noble metal based catalyst pairs (Pt/RuO2 or Pt/IrOx), more abundant and cheaper NiMo (HER) and NiFeOx (OER) compounds were prepared via electrodeposition. With the NiMo/NiFeOx catalyst pair we obtained ηSTH = 5.1% for a 64 cm2 size solar cell which was even better than the performance of the Pt/IrO2 system (ηSTH = 4.8%). In simulated day-night cycle operation the NiMo/NiFeOx catalyst pair showed excellent stability over several days. The experimental studies were successfully accompanied by simulation of the entire PV-EC device using a series connection model which allowed studies and pre-estimations of device performance by varying individual components such as catalysts, electrolytes, or solar cells. Based on these results we discuss the prospects and challenges of integrated PV-EC devices on large area for hydrogen and solar fuel production in general

Upscaling of integrated photoelectrochemical water-splitting devices to large areas

Photoelectrochemical water splitting promises both sustainable energy generation and energy storage in the form of hydrogen. However, the realization of this vision requires laboratory experiments to be engineered into a large-scale technology. Up to now only few concepts for scalable devices have been proposed or realized. Here we introduce and realize a concept which, by design, is scalable to large areas and is compatible with multiple thin-film photovoltaic technologies. The scalability is achieved by continuous repetition of a base unit created by laser processing. The concept allows for independent optimization of photovoltaic and electrochemical part. We demonstrate a fully integrated, wireless device with stable and bias-free operation for 40 h. Furthermore, the concept is scaled to a device area of 64 cm2 comprising 13 base units exhibiting a solar-to-hydrogen efficiency of 3.9%. The concept and its successful realization may be an important contribution towards the large-scale application of artificial photosynthesis

Tailoring copper foam with silver dendrite catalysts for highly selective carbon dioxide conversion into carbon monoxide

The present study outlines the important steps to bring electrochemical conversion of carbon dioxide (CO2) closer to commercial viability by using a large-scale metallic foam electrode as a highly conductive catalyst scaffold. Because of its versatility, it was possible to specifically tailor three-dimensional copper foam through coating with silver dendrite catalysts by electrodeposition. The requirements of high-yield CO2 conversion to carbon monoxide (CO) were met by tuning the deposition parameters toward a homogeneous coverage of the copper foam with nanosized dendrites, which additionally featured crystallographic surface orientations favoring CO production. The presented results evidence that Ag dendrites, owing a high density of planes with stepped (220) surface sites, paired with the superior active surface area of the copper foam can significantly foster the CO productivity. In a continuous flow-cell reactor setup, CO Faradaic efficiencies reaching from 85 to 96% for a wide range of low applied cathode potentials (<1.0 VRHE) along with high CO current densities up to 27 mA/cm2 were achieved, far outperforming other tested scaffold materials. Overall, this research provides new strategic guidelines for the fabrication of efficient and versatile cathodes for CO2 conversion compatible with large-scale integrated prototype devices.Authors acknowledge funding from Generalitat de Catalunya through the CERCA program, 2017 SGR 1246, 2017 SGR 327 and the Spanish MINECO projects MAT2014-59961, ENE2016-80788-C5-5-R and ENE2017-85087, together with the support from REPSOL S.A. ICN2 acknowledges the support from the Severo Ochoa Programme (grant no. SEV2017-0706). F.U. acknowledges the financial support from MINECO through Juan de la Cierva fellowship (FJCI-2016-29147).Peer reviewe

a-Si:H/µc-Si:H tandem junction based photocathodes with high open-circuit voltage for efficient hydrogen production

Thin film silicon tandem junction solar cells based on amorphous silicon (a-Si:H) and microcrystalline silicon (µc-Si:H) were developed with focus on high open-circuit voltages for the application as photocathodes in integrated photoelectrochemical cells for water electrolysis. By adjusting various parameters in the plasma enhanced chemical vapor deposition process of the individual µc-Si:H single junction solar cells, we showed that a-Si:H/µc-Si:H tandem junction solar cells exhibit open-circuit voltage over 1.5 V with solar energy conversion efficiency of 11% at a total silicon layer thickness below 1 µm. Our approach included thickness reduction, controlled SiH4 profiling, and incorporation of intrinsic interface buffer layers. The applicability of the tandem devices as photocathodes was evaluated in a photoelectrochemical cell. The a-Si:H/µc-Si:H based photocathodes exhibit a photocurrent onset potential of 1.3 V versus RHE and a short-circuit photocurrent of 10.0 mA/cm2. The presented approach may provide an efficient and low-cost pathway to solar hydrogen production

Modeling and practical realization of thin film silicon-based integrated solar water splitting devices

An integrated solar water splitting device based on thin film silicon multijunction photocathodes is presented. A graphical representation of the photovoltaic current–voltage data is introduced which allows for an estimation of the maximum achievable solar-to-hydrogen efficiency of the integrated device. Furthermore, a simple yet very useful series circuit model is used to predict the photoelectrochemical performance of the integrated device in a more elaborate way when the j–V characteristics of the individual components are known. Within the model, the j–V characteristics of each component can be either modeled with parameters from the literature or measured. The photocathode, the electrolyte concentration, and the hydrogen and oxygen evolving catalysts were varied exemplarily and the impact of each component on the integrated device performance was evaluated. A maximum solar-to-hydrogen efficiency of 9.5% was found using a triple junction solar cell functionalized with a Pt catalyst for the hydrogen evolution and a RuO2 catalyst for the oxygen evolution reaction in a 1 M KOH electrolyte. This result was confirmed experimentally and is compared to efficiencies reported in the literature

Tailoring Copper Foam with Silver Dendrite Catalysts for Highly Selective Carbon Dioxide Conversion into Carbon Monoxide

The present study outlines the important steps to bring electrochemical conversion of carbon dioxide (CO ) closer to commercial viability by using a large-scale metallic foam electrode as a highly conductive catalyst scaffold. Because of its versatility, it was possible to specifically tailor three-dimensional copper foam through coating with silver dendrite catalysts by electrodeposition. The requirements of high-yield CO conversion to carbon monoxide (CO) were met by tuning the deposition parameters toward a homogeneous coverage of the copper foam with nanosized dendrites, which additionally featured crystallographic surface orientations favoring CO production. The presented results evidence that Ag dendrites, owing a high density of planes with stepped (220) surface sites, paired with the superior active surface area of the copper foam can significantly foster the CO productivity. In a continuous flow-cell reactor setup, CO Faradaic efficiencies reaching from 85 to 96% for a wide range of low applied cathode potentials (<1.0 V ) along with high CO current densities up to 27 mA/cm were achieved, far outperforming other tested scaffold materials. Overall, this research provides new strategic guidelines for the fabrication of efficient and versatile cathodes for CO conversion compatible with large-scale integrated prototype devices