Photovoltaics integration in the Solar Decathlon pavilion : Assessing the implication of transparent BIPV with DSC technology on the indoor comfort and energy performance

Building-integrated photovoltaics (BIPV) are photovoltaic devices that are meant to replace conventional building components normally used in the building envelope. Different BIPV options are nowadays available on the market. Despite the lower nominal efficiency, 3rd generation cells, such as the Dye-sensitized Solar Cells (DSCs) are showing great potential in terms of architectural integration because of their light weight, higher sensibility in non-oriented position, availability in different colors and transparency. The main objective of the project is to assess the implication of DSC application on the thermal and visual indoor environment and on the energy performance of the Solar Decathlon pavilion designed by the Swiss team.

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

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

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.

2015

Formate as Anti-Oxidation Additives for Pb-Free FASnI(3) Perovskite Solar Cells

Jaeki Jeong, Jinhyun Kim, Jiyoun Seo

Pb-free Sn-based perovskite solar cells (PSCs) have significant potential for application in photovoltaic devices because oftheir suitable bandgap, low exciton binding energy, high carrier mobility, and long diffusion length. However, their performance is hampered by several issues. Sn-based perovskites are highly susceptible to oxidation, which induces a high concentration of defects and degrades the chemical stability of the perovskite crystals. Herein, the anion formate (HCOO-) can effectively suppress the oxidation of Sn in the pure formamidinium tin triiodide (FASnI(3)) perovskite without using A-site cationic additives. Moreover, the presence of formate results in a uniform pinhole-free perovskite film with a low trap density, reduced charge carrier recombination, and improved charge extraction. Density functional theory calculations show that formate-treated FASnI(3) has improved stability against oxidative Sn degradation. The formate-treated PSC achieves a power conversion efficiency of 12.11% at a high open-circuit voltage of 0.71 V. The device exhibits improved stability in ambient air in which it maintained over 80% of its initial power conversion efficiency after 180 min because oxidation is inhibited owing to the strong interaction between Sn and formate.

WILEY-V C H VERLAG GMBH2022

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

EPFL2006

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