Bandgap Tuning of Hydrogenated Amorphous Silicon via Carbon Incorporation for Semitransparent Photovoltaic Devices.

Gustavo Hernando Alvarez Suarez^a^,^b, PAU ESTARLICH GIL^a, Gerard Masmitjà Rusiñol^a, Alex J Lopez-Garcia^c, Jose Miguel Asensi Lopez^d, Cristobal Voz Sanchez^a, Joaquim Puigdollers^a, Alejandro Pérez Rodríguez^c^,^e

^aDepartament Enginyeria Electrònica, Universitat Politècnica Catalunya, c/ Jordi Girona 3-1, 08034, Barcelona, Spain.

^bFacultat de Física, Universitat de Barcelona (UB), C. Martí i Franquès 1-11, 08028 Barcelona, Spain.

^cInstitut de Recerca en Energia de Catalunya (IREC), Jardins de les Dones de Negre, 1, 2ª pl, 08930, Sant Adrià del Besòs, Barcelona, Spain.

^dIN2UB, Departament de Física Aplicada, Universitat de Barcelona, Carrer de Martí i Franquès 1-11, 08028, Barcelona, Spain.

^eIN2UB, Departament d’Enginyeria Electrònica i Biomèdica, Universitat de Barcelona, Carrer de Martí i Franquès 1-11, 08028, Barcelona.

Proceedings of MATSUS Fall 2025 Conference (MATSUSFall25)

A6 Advanced materials and device architectures for Transparent PV - #TransparentPV

València, Spain, 2025 October 20th - 24th

Organizers: Aldo Di Carlo and Alejandro Perez-Rodriguez

Poster, Gustavo Hernando Alvarez Suarez, 358
Publication date: 21st July 2025

Growing global energy demand and the climate crisis have highlighted the need for sustainable and decentralized energy systems. Traditional fossil fuel based power grids are increasingly being replaced by renewable and distributed solutions. Among these, solar energy stands out due to its abundance, scalability, and compatibility with urban environments.

However, conventional photovoltaic (PV) technologies face challenges for integration into architecturally sensitive settings, owing to their rigidity, opacity, and visual impact. This has fueled growing interest in transparent and semitransparent photovoltaic (TPV) technologies, which enable discreet, on-site energy generation. In particular, semitransparent photovoltaics (STPVs) offer a balance between efficiency, transparency, and aesthetics, making them highly attractive for Building-Integrated Photovoltaics (BIPV), despite presenting additional technical challenges.

This study focuses on the development of wide-bandgap inorganic STPVs based on ultrathin hydrogenated amorphous silicon (a-Si:H)[1] absorber layers combined with transparent electrodes. Bandgap tuning is achieved by incorporating carbon during absorber deposition, through adjustment of the precursor gas flows of silane (SiH₄) and methane (CH₄). Various SiH₄/CH₄ flow ratios were investigated, covering a range from carbon-rich compositions (a-SiCx:H) to intrinsic material (a-Si:H), enabling controlled modification of the optical and electronic properties of the device.

Devices fabricated with the structure SLG/FTO/AZO/a-SiCx:H(n)/a-SiCx:H/V₂Ox/AZO demonstrated strong performance across the range of absorber compositions. Power conversion efficiencies (PCE) ranged from 0.53%, with an average photopic transmittance (APT) [2] of 71% for a SiH₄/CH₄ flow ratio of 12/36 sccm, up to 2.6% PCE with 52% APT using a 48/0 sccm ratio (intrinsic material), achieving a light utilization efficiency (LUE) as high as 1.3[3]%.

Carbon incorporation increases the bandgap of the material, reducing optical absorption and consequently the short-circuit current density (Jsc). However, the wider bandgap also enhances the open circuit voltage (Voc) due to higher carrier energy levels, while Jsc is reduced, the increase in Voc can partially offset this loss, enabling optimization of semitransparent solar cell performance in applications that require both high transparency and elevated output voltage.

References:

[1] [1] Lopez‐Garcia, A. J., Alvarez‐Suarez, G., Ros, E., Ortega, P., Voz, C., Puigdollers, J., & Pérez Rodríguez, A. (2024). Enhanced Selective Contact Behavior in a‐Si: H/oxide Transparent Photovoltaic Devices via Dipole Layer Integration. Solar RRL, 8(14), 2400276.

[2] [2] Traverse, C. J., Pandey, R., Barr, M. C., & Lunt, R. R. (2017). Emergence of highly transparent photovoltaics for distributed applications. Nature Energy, 2(11), 849-860.

[3] [3]Alvarez‐Suarez, G., Lopez‐Garcia, A. J., Estarlich, P., Asensi, J. M., Masmitjà, G., Ortega, P., ... & Perez Rodriguez, A. (2025). Exploring the Limits and Balancing Efficiency, Transparency, and Esthetics in Ultrathin a‐Si: H Transparent Photovoltaic Devices. Solar RRL, 2400816.

Acknowledgements:

This work was funded by MCIN/AEI/10.13039/501100011033 with grant numbers PID2022-138434OB-C51 (SCALING) and TED2021-129758B-C32 (TransEl). TransEl project is also funded by the European Union “NextGenerationEU”/PRTR program. P. Estarlich acknowledges financial support from the Spanish Ministry for Digital Transformation and Public Administration and the European Union – NextGenerationEU, under grant agreement (TSI-069100-2023-0015).

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