The development of TPV devices has gained significant attention in recent years due to their potential for seamless integration into Building-Integrated Photovoltaics (BIPV). BIPV has been identified as a key enabling technology for the development of "Near Zero Energy Buildings" (NZEB), achieved through the integration of a new generation of PV modules capable of replacing traditional architectural elements. TPV devices are also of interest in other applications, such as Product-Integrated Photovoltaics (PiPV), and any scenarios where aesthetics are important. TPV devices have the potential to revolutionize photovoltaic technology by enabling on-site generation while minimizing visual impact.

One of the most promising approaches to achieve TPV is to utilize the ultraviolet region of the solar spectra, while avoiding absorption in the visible range and more specifically on the photopic response range of the human eye, thus attaining complete apparent transparency. One promising approach to achieve high transparency on solar cells is by using wide bandgap materials with bandgap energy (E_g) above 2.7 eV. However, the choice of absorber material is critical, due to the lower number of photons in this spectral region, making it a must to have a good spectral match with the bandgap and the UV onset to maximize photon absorption. In this way, ZnO_1-xS_x has been proposed as an ideal UV absorber thanks to a composition-tunable bandgap that can shift from 3.2 eV (pure ZnO) down to 2.7 eV (x=0.5) by anionic substitution of oxygen by sulfur. ZnO_1-xS_x is a material composed of earth-abundant raw elements, compatible with scalable fabrication processes and can be synthesized at low temperatures, which potentially allows minimizing the carbon footprint, economic costs and energy expenditure associated with device manufacturing.

In this work we present a fully oxide based solar cells with structure SGL/FTO/MoO_x/ZnO_1-xS_x/ZnO/AZO. This device is a full ALD-compatible process, which enables high process reproducibility and conformality for the coverage of 3D structures. We explore the different compositional ranges from sulfur rich to sulfur poor and how it affects to performance, also crystal formation and phase segregation is explored at different synthesis temperatures. In a second level, two samples with different HTL are prepared and studied, one with MoO_x and another with NiO. Based on these prelimienary results, we explore an aproach to significantly increase the Voc of the ZnO_1-xS_x TPV solar cells by the fine tuning of the MoO_x HTL thickness, preparing two 5x5 cm² samples with a gradient of the MoO_x HTL layer. The complete optimized structure demostrated an Average Photopic Transmittance of 73%, showing indeed excelent transparency, while achieving colore rendering Index (CRI) of 97, coriming its high color neutrality and achieving record-high Voc values close to 800 mV.