Transparent Photovoltaic (TPV) technologies represent a promising branch within photovoltaics, seeking to expand their applications by overcoming challenges related to on-site integration, especially within architectural elements related to Building Integrated PV (BIPV), and more recently, also in the areas of Indoor PV (IPV), IoT and Agrivoltaics (APV). Unlike conventional approaches solely focused on efficiency, TPV introduces two additional dimensions: transparency and aesthetics, which pose added challenges to the device architecture. Moreover, for TPV technologies to be translated into competitive products it is critical to work on low-cost, sustainable and stable materials and fabrication processes that at least meet the stringent requirements for any PV technologies in conjunction with the transparency and aesthetic values that allow for seamless integration.

The goal for TPV is to have a device that absorbs in the visible range as little as possible while it absorbs the remainder part of the spectrum (i.e. UV/IR) in order to be visible transparent to the human eye, and as so, it can be split into two main categories or approaches, namely wavelength-selective and non-wavelength-selective. These two approaches are being actively investigated using different materials, such as organic materials and perovskites. However, inorganic-based structures constitute a very attractive prospect as they can be integrated as different functional layers in the solar cell architecture (i.e. as absorber, Charge Transport Layer and transparent electrical contacts). Additionally, many inorganic materials present high bandgap, tuneable conductivity, low deposition temperatures and can be deposited by a plethora of techniques that are possible to upscale for industrial purposes. Another key aspect is that these materials are stable, have low thermal budgets and are CRM-free. Given these aspects the challenge is on how to combine them in advanced device architectures to develop a final device that is efficient, transparent and aesthetically pleasing that can be integrated in architectural components (windows, canopies, façades) and/or on devices that present low power draws such as smartphones, wearables and IoT devices and sensors.

Herein, we will discuss the basic principles and figures of merit in TPV, as well as the state of the art for inorganic-based strategies. The talk will also focus into two main approaches that we are developing: ZnO1-xSx UV-selective absorbers and on the optimisation of oxide-based architectures integrating nanometric a-Si:H layers as a non-wavelength-selective approach. Main challenges and late results attained with both strategies will be reviewed, including the achievement of record devices with Light Utilisation Efficiency (LUE) up to 2.3%, transparency in the range between 30% and 70% and photoconversion efficiencies up to 5%.