ENERGY HARVESTING IN CITIES WITH TRANSPARENT AND HIGHLY EFFICIENT WINDOW-INTEGRATED MULTI-JUNCTION SOLAR CELLS

Project Information

CITYSOLAR

Grant agreement ID: 101007084

DOI

10.3030/101007084

Project closed

EC signature date 3 November 2020

Start date 1 December 2020

End date 30 April 2024

Funded under

• SOCIETAL CHALLENGES - Secure, clean and efficient energy

Total cost

€ 4 765 768,75

EU contribution

€ 3 779 242,00

Coordinated by

CONSIGLIO NAZIONALE DELLE RICERCHE
Italy

Periodic Reporting for period 2 - CITYSOLAR (ENERGY HARVESTING IN CITIES WITH TRANSPARENT AND HIGHLY EFFICIENT WINDOW-INTEGRATED MULTI-JUNCTION SOLAR CELLS)

Reporting period: 2022-06-01 to 2024-04-30

Summary of the context and overall objectives of the project

Transparent photovoltaics (TPV) possesses a huge untapped potential in the harvesting of solar energy where it readily can be embedded in buildings applications worldwide to significant reduce CO2 emissions, and support the needed development of nearly zero-energy buildings. TPV will increase the utilization of renewable energy directly where it is needed, and play a crucial role for the sustainable transformation of the energy sector in large cities. In the CITYSOLAR project, a new breakthrough concept for TPV have been developed by exploiting the combined use of emerging technologies, namely multi-junction solar modules developed from near-ultraviolet perovskite solar cells (NUV-PSC) and near-infrared organic solar cells (NIR-OPV). Using advanced concepts within light management such as photonic crystals, nanophotonics and photon recycling and advanced module integration schemes, CITYSOLAR radically changed the performance limits for TPV by significantly reducing losses related to light absorption and scale-up from individual solar cells to multi-junction modules.
CITYSOLAR project was able to demonstrate the design, fabrication and characterization of a new concept of see-through PV, namely the use of tandem module in a two and four terminal configuration with efficiency exceeding 12.3% and visual transparency of almost 30% and a good Colour Rendering index of 77. The demonstration of the CITYSOLAR technology already at module level, as well the use of completely scalable techniques for the realization of the modules will permit a direct exploitation of the results. This has been confirmed by the fabrication of BIPV prototypes on 40x40 cm2 and 60x60 cm2.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the second period (M19-M21) we finalize the project reaching as much as was possible the goal of the project.

The CITYSOLAR project has made significant strides in optimizing transparent photovoltaic (TPV) devices and modules over the past 23 months. The key achievements can be summarized as in the following:
By optimizing the device stack, including perovskite thickness and passivation strategies, as well as light management tools (front and rear anti-reflective coatings, ARCs), the semi-transparent perovskite solar cells (PSCs) achieved a power conversion efficiency (PCE) of 8.1% and an average visible transmittance (AVT) of 70.7%. This resulted in a Light Utilization Efficiency (LUE) of 5.72 the highest reported for TPV. Alternative perovskite absorbers such as CsPbBr3 and Cs2AgBiBr6 were tested, enhancing scientific knowledge for their use in Internet of Things (IOT) and building-integrated photovoltaics (BIPV).
Detailed analyses and optimization of systems like PCE10 and PM6 donors led to the highest reported PCEs of 7.3%, AVT of 47%, and a CRI of 85 for OPV modules. Sun degradation tests indicated a T80 lifetime of around 400 hours.
We successful scaling of NUV perovskite solar cells and modules, with 100 cm²-aperture area modules achieving a PCE of 7.1% and an AVT of 65%. The PM6 donor absorber achieved a PCE of 7.2%, AVT of 43%, LUE of 3.1%, and a CRI of 85 in 100 cm² modules.
NIR and NUV distributed Bragg reflectors (DBRs) were fabricated to enhance OPV and PSC device performance. The incorporation of light outcoupling layers like Al2O3 further improved LUE.
Base on the advances on the separated NUV and NIR modules, we developed four-terminal (4T) and two-terminal (2T) tandem devices, achieving a PCE of 12.32%, AVT of 29.6%, LUE of 3.64%, and CRI of 77.09.
Overall, these developments represent a new state-of-the-art for semi-transparent modules, significantly advancing the field of TPV and BIPV applications.
Detailed process was developed to integrate semi-transparent PSC and OPV into novel tandem solar cells. These were implemented in mini-modules with high performance and laminated into larger arrays for practical applications. Two configurations (2x2 and 3x3 arrays) of multijunction modules were integrated into solar windows, transforming them into energy-producing units with significant power output.
An ex-ante life cycle assessment (LCA) compared TPV devices to silicon PV alternatives, showing better material use despite laboratory-scale data.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Overall, the developments in CITYSOLAR represent a new state-of-the-art for semi-transparent modules, significantly advancing the field of TPV and BIPV applications. In particular we advanced the NUV-PSC modules reaching a LUE of 5.72% for cells and above 4.5% for modules. Similarly, the NIR-OPV achieved a LUE of 3.85% with an efficiency of 8.2% and a Colour Rendering Index (CRI) of 85. A similar LUE (3.1) was achieved for semi-transparent modules. However, the most significant progress of CITYSOLAR was the design, fabrication and characterization of the Tandem semi-transparent module. This has never shown before and represents a breakthrough in the field of see-through PV. Here we were able to show a LUE of 3.7% on a module realized on a 5x5 cm2 substrate with an efficiency of 12.32% and a CRI of 77.
An ex-ante LCA was performed for a complete environmental profile of the TPV device. In the study, the TPV was compared to the most available silicon PV alternative on the market both in terms of manufacturing of the cells and the electricity production. This comparison showed a better use of materials than silicon options considering the manufacturing, even though data for the TPV device come from the laboratories meaning that quantities are often overestimated. It was suggested at the end of the study a risk assessment for the presence of Lead in the TPV device, however the LCA showed minimal impact due to limited use of this element.
The exploitation plan, defined with the EU's Booster service, identified three main Key Exploitable Results (KERs) connected to several partners of the project.

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