Experimental Determination of Optical and Thermal Properties of Semi-transparent Photovoltaic Modules Based on Dye-sensitized Solar Cells

Olivia Valérie Charlotte Bouvard, Josef Andreas Schuler, Sara Vanzo
2015
Article de conférence

Résumé

The demand for energy efficiency of buildings and on-site electricity production is rising. Building integrated photovoltaic can provide a part of the electricity demand. Many studies are related to the module efficiency. However, architectural integration, optical and thermal properties also require attention. Semi-transparent modules are especially interesting for architectural integration in the glazed part of the façade. Dye sensitized solar cells, offering color and semi-transparency, are in the process of market introduction. However, dye-sensitized solar cells are fragile and there are not many examples of architectural integration due to the technical challenge of introducing these cells in a glazing. A glazing containing colored photovoltaic modules could be used to design an active façade. In order to determine the thermal behaviour of the building, the precise optical and thermal properties of the used materials need to be known. Performances of semi-transparent photovoltaic modules based on dye-sensitized solar cells were investigated. These modules come from the same manufacturer, using the same technology. However, they differ in terms of shades and nuances. Common practice is to indicate optical properties at normal angle of incidence. Yet, for most latitudes, the properties for a large range of angles of incidence are more relevant. Therefore, the spectral transmittance and the reflectance were measured at 12 angles of incidence ranging from 0° to 75°. From these data, the solar direct transmittance τe, the solar direct reflectance ρe and the visible transmittance τv and selectivity were calculated. The solar gain factor was determined on a prototype double glazing under illumination with a solar simulator by measuring the temperatures of the external and inner surface of the product. Combined with the values of absorptance obtained from the transmittance and reflectance values, this measurement allows us to determine the internal heat transfer coefficient qi and thus the solar gain factor of the double glazing (also called total energetic transmittance or g-value). Final performance of a façade containing these modules will depend on the composition of the double glazing in which they will be laminated. The performance of the module itself will help to determine the best composition for each climate. For instance, a solar protection coating may be needed. The modules can be laminated to a glass pane and then be assembled in a double glazing. Therefore the architectural integration is facilitated and compatible with existing façade systems. In highly glazed building, a part of the façade could then be a photovoltaic façade and deliver a fraction of the energy demand while providing colourful options to enhance the aesthetic of the building.

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Olivia Valérie Charlotte Bouvard, Josef Andreas Schuler, Sara Vanzo
2015
Article de conférence

Résumé

Official source

https://infoscience.epfl.ch/record/215033?ln=fr

À propos de ce résultat

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Dye-sensitized solar cells (DSCs) constitute a novel class of hybrid organic-inorganic solar cells. At the heart of the device is a mesoporous film of titanium dioxide (TiO2) nanoparticles, which are coated with a monolayer of dye sensitive to the visible region of the solar spectrum. The role of the dye is similar to the role of chlorophyll in plants; it harvests solar light and transfers the energy via electron transfer to a suitable material (here TiO2) to produce electricity — as opposed to chemical energy in plants. DSCs are fabricated of abundant and cheap materials using inexpensive processes (e.g. screen-printing) and are likely to be a significant contributor to the future commercial photovoltaic technology portfolio. The work conducted during this thesis aimed at optimizing the DSC using three different strategies: The use of versatile organic sensitizers for stable and efficient DSCs, the study of tandem device architectures in combination with other solar cells to harvest a larger fraction of the solar spectrum, and the development of a validated optoelectric model of the DSC. Organic donor-π-acceptor dyes are an interesting alternative to the standard metal-organic complexes used in DSCs. Efficient photovoltaic conversion and stable performance could be demonstrated with three classes of donor systems, namely diphenylamine, difluorenylaminophenyl, and π-extended tetrathiafulvalene. The highest conversion efficiencies were obtained with a difluorenylaminophenyl donor system (η = 8.3 % with a volatile electrolyte and η = 7.6 % with a solvent-free ionic liquid, which was a new record for organic dyes at the time of publication). Surprisingly, efficient regeneration of the oxidized dye by the I-/I3- redox mediator was found with the π-extended tetrathiafulvalene system, even though the thermodynamic driving force was as low as 150 mV. So far driving forces of 300-500 mV had been regarded as necessary for efficient regeneration of the dye cation. Also, important structure-property relationships pertaining to the recombination of electrons with the electrolyte and to the stability of the device could be identified (i.e. effect of linear vs. branched structure, linker length, and moieties used). The power conversion efficiency of solar cells can be extended beyond the limit for a single cell (∼ 30 %) by using multiple cells with different optical gaps in a tandem device. DSCs and chalcopyrite Cu(In,Ga)Se2 (CIGS) solar cells have complementary optical gaps and are thus suitable systems for integration in a tandem device. It was shown that a monolithic DSC/CIGS tandem device has the potential for increased efficiency over a mechanically stacked device due to increased light transmission to the bottom cell, and a monolithic DSC/CIGS device with an initial efficiency of η = 12.2 % was demonstrated. The degradation of the devices — induced by the corrosion of the CIGS cell in contact with the I-/I3- redox mediator — could be retarded with a protective thin conformal ZnO/TiO2 oxide layer coated on the CIGS cell by atomic layer deposition. Finally, an experimentally validated optical and electrical model of the DSC has been developed to assist the optimization process, which is predominantly conducted by empirical means in the DSC research community. The optical model allows to accurately calculate the internal quantum efficiency of devices, i.e. the ratio of extracted electrons to absorbed photons by the dye, a crucial and so far difficult to determine characteristic. Intrinsic parameters — like injection efficiency, electron diffusion length, or distribution of trap states in the TiO2 — can be extracted from experimental steady-state and time-dependent data with the electric model. The model allows to make a comprehensive and quantitative loss analysis of the different optical and electric loss channels in the DSC. The model has been implemented with a graphical user interface for straightforward usage. All three optimization strategies — organic dyes, tandem architecture, and device modeling — developed during this thesis make a valuable contribution to the development and commercialization of inexpensive and high efficiency DSCs. They enable a comprehensive view of the system and pave the way for a systematic analysis and reduction of losses, which has been the ultimate route to success for several established photovoltaic technologies.

EPFL2010

Chargement

Novel organic dyes for enhanced red to near IR response in dye sensitised solar cells

The aim of this work was to develop new, organic dyes, capable of harvesting photons in the red to near-IR region of the spectrum. A series of squaraine and tricarbocyanine dyes were produced and characterised and their optical and redox properties studied. The results of initial photovoltaic tests, followed by optimisations of cell performance, have also been presented. These clearly demonstrate the effectiveness of these dyes in solar cells. A total of 12 new squaraine dyes were successfully synthesised, seven of which were tested in "dye-sensitised" solar cells. The efficiencies ranged from 1.2%-3.7%, for the best dye [B1]. It was concluded that enhanced performance could be achieved in the presence of chenodeoxycholic acid (CDCA) and tetrabutylpyridine (TBP). These additives both help to prevent aggregation and increase the cell potential, limiting charge collection losses and enhancing performance. Three new tricarbocyanine dyes were also synthesised, two of which were used in solar cells. Unfortunately, due to the interaction of [B12] with the electrolyte, the dye proved to be unstable, as both the absorption maxima in UV-vis and fluorescence emission wavelengths were shifted to higher energies. Thus, the red response of the dye was significantly reduced and photovoltaic performance hindered. A limited photo-response of [B14] was also seen, although this dye appeared to be very stable in the presence of the electrolyte. To deduce the possible reasons for the poor performance of these dyes, their optical and electrochemical properties were investigated. Thus, cyclic voltametry was employed to identify the redox potentials of the dyes and their charge injection and recombination dynamics were studied through nanosecond time-resolved transient laser spectroscopy. It was concluded that the dyes theoretically possess the ideal characteristics for solar cell function and that the problem of [B14] lay in the purity of the dye. [B14] proved to be very difficult to purify as the dye was unstable in solution and decomposed on the columns employed in chromatography. Fortunately the dye appeared to be stable in the presence of an electrolyte when adsorbed on TiO2. The dye gave an IPCE of 12% between 800 – 900nm, which is particularly impressive, especially if the purity of the dye is considered. A new method of purification must be found however, if photovoltaic performance is to be enhanced. Finally, the effects of a compact blocking layer on device performance were studied. It was clearly demonstrated that a compact layer was essential. This was investigated and a relationship between the structure of the dye and the necessity of the blocking layer was established.

EPFL2006

Chargement

Active façades : life cycle environmental impacts and savings of photovoltaic power plants integrated into the building envelope

Gianluca Cattaneo, Angela Clua Longas

Aim and approach used Increased energy supply from photovoltaics is a main priority in the “Energy Strategy 2050”. Within the joint research project "Next generation photovoltaics" funded by the Swiss National Science Foundation, we analysed different options for the enhanced integration of photovoltaic technologies into the envelope of Swiss buildings (BIPV). The PV modules for building integration are using novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC) with adaptions to improve the visual acceptance. In a joint effort of product developers, architects and scientists, this project aimed at providing pathways for the wide-scale use of BIPV façade solutions, and developing integrated designs based on emerging high-efficiency module technologies to improve the visual aspect and acceptance of PV systems installed in Switzerland. These so-called active façades incorporating BIPV modules to generate electricity can provide a significant contribution to the energy transition away from fossil and nuclear fuels. We compared the environmental impacts of different façade construction systems with and without SHJ-PSC BIPV modules with improved visual design, using a prospective life cycle assessment with a time horizon of 2025. The comparison includes a conventional brick and roughcast façade, a timber frame façade, and the Advanced Active Façade (AAF), which integrates SHJ-PSC BIPV modules in a low embodied impact façade substructure. In addition, we compared the environmental impacts caused by the construction of the above described façades with the environmental impacts saved due to the electricity produced by BIPV modules incorporated into the AAF. 2. Scientific innovation and relevance Our research focuses on the combined expertise of life cycle thinking, PV module development and façade design. The major scientific innovations are: 1) the prospective life cycle assessment of novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC); 2) the comparison of different façade construction systems and their environmental impacts; 3) the quantification of the saved environmental impacts arising from the electricity generated by the active façade; and 4) the visual adjustments of PV modules to improve their acceptance. The main advantage of integrating PV into building façades is the large available area, which can be limited on rooftops. In order to reach the market penetration for PV required for the energy transition, PV modules must be integrated into façades as well as into rooftops. 3. Results and conclusions An equilibrium must be achieved among different technical and aesthetic issues when integrating energy generation systems into the building envelope, especially into the façade for its public condition and exposure. Based on these prerequisites, the research team has developed the AAF which combines passive and active energy design strategies while meeting contemporary architectural requirements. This façade design is based on low-embodied-energy construction principles, it is defined by a non-loadbearing wood-panel substructure and it integrates a double layer of natural insulation: cellulose and wood-fibre. In addition, its design incorporates an opaque SHJ-PSC BIPV façade-cladding following contemporary façade design trends. (Figure 1). The use of photovoltaic modules integrated into the façade cladding or roof will increase the environmental impact of the building envelope, compared to using conventional construction materials. The environmental impacts of the AAF using PV modules are two to four times higher compared to a conventional façade. The PV modules cause the highest share of greenhouse gas emissions of the AAF with about 375 kg CO2-eq per square meter (see Figure 2). The additional materials required to build the AAF including exterior panels, insulation and other materials cause about 75 kg CO2-eq per square meter of façade. The brick and timber frame façades cause greenhouse gas emissions around 200 and 100 kg CO2-eq, respectively. If the greenhouse gas emissions caused by the PV module is excluded this will result in a reduction between 25 and 125 kg CO2-eq per square meter of façade. However, the environmental impacts of the AAF are significantly reduced if the whole life cycle is considered due to the PV electricity produced by the building. Therefore, we calculated the saved greenhouse gas emissions due to the electricity produced by the advanced active façade and fed to the European electricity grid using the greenhouse gas emissions caused by the current European electricity mix as reference. These calculated savings due to the electricity produced by the BIPV are about 4 times higher than the impacts of the advanced active façade. Incorporating BIPV panels into building’s façades will cause net savings of about 1700 kg CO2-eq per square meter over the whole life cycle of BIPV façades, while simultaneously saving up to 125 kg CO2-eq per square meter of façade for the reduced material demand to build the façade (see Figure 3). We performed this analysis for 16 different environmental impacts according to the recommended midpoints by the Joint Research Council of the European Commission. The results were comparable to greenhouse gas emissions with the net saved environmental impacts being many times higher for all the environmental impacts analysed except mineral resource use caused by the indium used in the novel SHJ-PSC tandem module (see Figure 4). To conclude, the use of PV modules in AAF can reduce the greenhouse gas emissions per square meter of façade between 25 and 60 % if the production of the PV module and its produced electricity are excluded. If the production and life cycle of the PV modules are included into the analysis the AAF will cause net greenhouse gas savings up to four times higher than the production of the AAF itself. The results for environmental impacts other than greenhouse gases were similar except for mineral resource depletion. Overall, the building integration of photovoltaic modules as AAF will reduce the environmental impacts of the building while simultaneously providing a visually appealing building envelope.

2019

Chargement

Afficher plus

Novel organic dyes for enhanced red to near IR response in dye sensitised solar cells

EPFL2006

Active façades : life cycle environmental impacts and savings of photovoltaic power plants integrated into the building envelope

Gianluca Cattaneo, Angela Clua Longas

Aim and approach used Increased energy supply from photovoltaics is a main priority in the “Energy Strategy 2050”. Within the joint research project "Next generation photovoltaics" funded by the Swiss National Science Foundation, we analysed different options for the enhanced integration of photovoltaic technologies into the envelope of Swiss buildings (BIPV). The PV modules for building integration are using novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC) with adaptions to improve the visual acceptance. In a joint effort of product developers, architects and scientists, this project aimed at providing pathways for the wide-scale use of BIPV façade solutions, and developing integrated designs based on emerging high-efficiency module technologies to improve the visual aspect and acceptance of PV systems installed in Switzerland. These so-called active façades incorporating BIPV modules to generate electricity can provide a significant contribution to the energy transition away from fossil and nuclear fuels. We compared the environmental impacts of different façade construction systems with and without SHJ-PSC BIPV modules with improved visual design, using a prospective life cycle assessment with a time horizon of 2025. The comparison includes a conventional brick and roughcast façade, a timber frame façade, and the Advanced Active Façade (AAF), which integrates SHJ-PSC BIPV modules in a low embodied impact façade substructure. In addition, we compared the environmental impacts caused by the construction of the above described façades with the environmental impacts saved due to the electricity produced by BIPV modules incorporated into the AAF. 2. Scientific innovation and relevance Our research focuses on the combined expertise of life cycle thinking, PV module development and façade design. The major scientific innovations are: 1) the prospective life cycle assessment of novel monolithic silicon heterojunction organometallic perovskite tandem cells (SHJ-PSC); 2) the comparison of different façade construction systems and their environmental impacts; 3) the quantification of the saved environmental impacts arising from the electricity generated by the active façade; and 4) the visual adjustments of PV modules to improve their acceptance. The main advantage of integrating PV into building façades is the large available area, which can be limited on rooftops. In order to reach the market penetration for PV required for the energy transition, PV modules must be integrated into façades as well as into rooftops. 3. Results and conclusions An equilibrium must be achieved among different technical and aesthetic issues when integrating energy generation systems into the building envelope, especially into the façade for its public condition and exposure. Based on these prerequisites, the research team has developed the AAF which combines passive and active energy design strategies while meeting contemporary architectural requirements. This façade design is based on low-embodied-energy construction principles, it is defined by a non-loadbearing wood-panel substructure and it integrates a double layer of natural insulation: cellulose and wood-fibre. In addition, its design incorporates an opaque SHJ-PSC BIPV façade-cladding following contemporary façade design trends. (Figure 1). The use of photovoltaic modules integrated into the façade cladding or roof will increase the environmental impact of the building envelope, compared to using conventional construction materials. The environmental impacts of the AAF using PV modules are two to four times higher compared to a conventional façade. The PV modules cause the highest share of greenhouse gas emissions of the AAF with about 375 kg CO2-eq per square meter (see Figure 2). The additional materials required to build the AAF including exterior panels, insulation and other materials cause about 75 kg CO2-eq per square meter of façade. The brick and timber frame façades cause greenhouse gas emissions around 200 and 100 kg CO2-eq, respectively. If the greenhouse gas emissions caused by the PV module is excluded this will result in a reduction between 25 and 125 kg CO2-eq per square meter of façade. However, the environmental impacts of the AAF are significantly reduced if the whole life cycle is considered due to the PV electricity produced by the building. Therefore, we calculated the saved greenhouse gas emissions due to the electricity produced by the advanced active façade and fed to the European electricity grid using the greenhouse gas emissions caused by the current European electricity mix as reference. These calculated savings due to the electricity produced by the BIPV are about 4 times higher than the impacts of the advanced active façade. Incorporating BIPV panels into building’s façades will cause net savings of about 1700 kg CO2-eq per square meter over the whole life cycle of BIPV façades, while simultaneously saving up to 125 kg CO2-eq per square meter of façade for the reduced material demand to build the façade (see Figure 3). We performed this analysis for 16 different environmental impacts according to the recommended midpoints by the Joint Research Council of the European Commission. The results were comparable to greenhouse gas emissions with the net saved environmental impacts being many times higher for all the environmental impacts analysed except mineral resource use caused by the indium used in the novel SHJ-PSC tandem module (see Figure 4). To conclude, the use of PV modules in AAF can reduce the greenhouse gas emissions per square meter of façade between 25 and 60 % if the production of the PV module and its produced electricity are excluded. If the production and life cycle of the PV modules are included into the analysis the AAF will cause net greenhouse gas savings up to four times higher than the production of the AAF itself. The results for environmental impacts other than greenhouse gases were similar except for mineral resource depletion. Overall, the building integration of photovoltaic modules as AAF will reduce the environmental impacts of the building while simultaneously providing a visually appealing building envelope.

2019

EPFL2010