Ultrathin a-Si:H/Oxide Transparent PV Devices Deposited onto Architectural-Compatible Glass and Ceramic Substrates

Transparent Photovoltaics (TPV) is an emergent branch in the toolkit of PV that promises to extend the potential applications of PV and complement the most mature strategies that are limited in terms of on-site integration and applicability, especially into architectural components.^[1] The most important feature of PV devices is power output (i.e. efficiency). However, this approach brings in another critical feature almost at the same level of importance, which is the transparency and aesthetics of the device, which have to meet certain standards that can differ depending on the specific application and/or integration. As such, it adds some degree of complexity when optimizing, as other properties become more important. For TPV to be implemented in real-world scenarios they do not need to compete with high efficiency devices, rather they must be tailored to maximize efficiency with special care on transparency and aesthetic characteristics. For cost competitiveness, existing and mature industrialized materials (earth-abundant and non-toxic) and processes are a good starting point for first implementations. Developing such devices can potentially allow for fast-developing integration in areas such as building-integrated PV (BIPV) in the form of façade windows and other glazing elements, or to be integrated ubiquitously into sensors and future IoT devices with low-power requirements, as well as in Agrivoltaics (APV). Recent work has effectively studied the use of a-Si :H/oxide structures on glass substrates for TPV, showing some limitations especially in terms of V_oc.^[2,3]<br/>In this work, we present inorganic-based TPV devices relying on ultrathin a-Si:H as absorber and different oxides as carrier selective contacts and transparent electrodes. In an innovative approach, we have inserted a high dipolar moment molecule (PAMAM-G3 dendrimer) at the ETL/absorber interface. This interface modification allows working with oxide charge transport layers (CTLs) that offer high transparency while eliminating surface energy barriers that decrease the resulting V_oc of the device, avoiding doping strategies (i.e. a-Si:H(p), a-Si:H(n)) and reducing costs due the low-temperature deposition processes. This new solution has allowed a record Light Utilization Efficiency (LUE) of 0.85%, by improving V_oc from 410 (reference) to 781 mV (PAMAM G3), still not reached by state-of-the-art devices with these materials, with negligible reduction in Average Photopic Transmittance or Color Rendering Index. The basic device structure is SLG/FTO/AZO/PAMAM-G3/ZnO/a-Si:H(30nm)/MoO₃/ITO. At the present time, spectrophotometry and J-V measurements under AM1.5G illumination (from the front and back sides) as well as Spectral Response measurements have been carried out. We report also on the bifaciality aspect of the architecture, showing almost unity bifacial factor, due to the ultrathin absorber coupled to wide-bandgap CTLs that make the device optically symmetric. Additionally, reference devices without dipoles have been also deposited onto ceramic substrates successfully and will be presented, confirming the potential of this approach to be integrated in different architectural environments such as glass and ceramics.<br/>The work presented is of high relevance for the development of the field of inorganic thin film Transparent PV technologies, especially those working on ultrathin absorbers. It might also spark interest in thin film technologies in general that rely on advanced ETL/Active layer/HTL architectures.<br/>This work has received funding from MCIN/AEI/10.13039/501100011033 under grant numbers PID2019-109215RB-C41 and TED2021-129758B-C32 and by the NextGeratiouEU/PRTR.<br/>[1] C. J. Traverse, R. Pandey, M. C. Barr, R. R. Lunt, <i>Nat. Energy</i> <b>2017</b>, <i>2</i>, 849.<br/>[2] S. Kim, M. Patel, T. T. Nguyen, J. Yi, C. P. Wong, J. Kim, <i>Nano Energy</i> <b>2020</b>, <i>77</i>, 105090.<br/>[3] A. J. Lopez-Garcia, O. Blazquez, C. Voz, J. Puigdollers, V. Izquierdo-Roca, A. Pérez-Rodríguez, <i>Sol. RRL</i> <b>2022</b>, <i>6</i>, 2100909.