Thin film photovoltaics (PV) have historically played second fiddle, dwarfed by the multi-billion US dollar silicon PV industry. This may be about to change.

Emerging PV applications, such as indoor energy harvesting and building integrated PV, have specific requirements that will enable thin film silicon alternatives to flourish.

Thin film PV delivers several advantages relative to the incumbent technology, including lighter weight, better power conversion efficiency under indoor light, simpler manufacturing, and potentially lower costs. A particularly exciting opportunity is the role of thin film photovoltaics in powering Internet of Things (IoT) devices.

The variety of thin film PV technologies, including perovskite, dye sensitized, organic, cadmium telluride, and copper indium gallium selenide – along with their potential for multiple promising applications – is assessed in IDTechEx’s recent report, “Thin Film & Flexible Photovoltaics 2023-2033”. In addition, IDTechEx has published “Perovskite Photovoltaics 2023-2033”, a report that provides an in-depth technical and commercial insight into the nascent perovskite market.

Perovskite PV has been gaining increasing momentum over the past decade. Since its emergence in 2009, substantial research activity has led to the fastest acceleration in record efficiency of any other PV technology. Its record efficiency is currently just 1% below that of the highest efficiency silicon solar cells, a material that has been researched for decades.

The excitement surrounding perovskite PV is not only related to its high efficiency but also to its versatility. Perovskite is made from inexpensive and abundant raw materials such as lead iodide that can be printed, thus enabling high throughput low-cost manufacturing. Perovskite solar cells also maintain a reasonably high efficiency under low light intensity and even indoor artificial lighting.

Although as an early-stage technology it is not yet deployed commercially, developers are working towards integrating perovskite PV into self-powered devices and Internet of Things (IoT). IoT devices promise to enable a world of smart, connected objects, with their number expected to accelerate rapidly to over 20 billion by 2030.

Powering so many devices with rechargeable or disposable batteries is time consuming, expensive, and not environmentally friendly. The integration of an inexpensive thin film solar module within smart electronics means a steady supply of energy can be delivered without needing to recharge or replace batteries.

Perovskite PV is not limited to electronics. Due to its high-power density, it is also being developed for utility scale and residential PV, with medium-scale projects already under development.

The UK company, Oxford PV, has made a particularly exciting step forward by combining the perovskite with silicon to produce tandem modules that can deliver efficiencies higher than any other PV technology available on the market at ~27 %. Thin film PV is often discussed as silicon’s competition. However, the tandem modules are an excellent demonstration of how conventional and emerging technologies can complement each other. Oxford PV’s tandem modules are expected to reach the market in 2023.

Solution Processable PV – A New Era for Photovoltaics

One of the key drivers pushing thin film photovoltaics closer to the spotlight is the possibility of easily scalable solution processing. Solar cells made from perovskite, organic, and dye-sensitized materials can be fabricated within moments, with each layer deposited as a solution using standard methods such as inkjet printing or slot-die coating.

Printing and coating methods are well suited to roll-to-roll manufacturing and economical solar cell fabrication. The simplicity allows manufacturers a high degree of independence and the ability to carry out every step of the solar cell fabrication in-house.

Solution-processability is a key strategic differentiator for thin film PV. While the conventional PV industry depends on the complicated and energy-intensive production of silicon, solution-processable PV uses in-situ¬ synthesis of the cells layers typically carried at relatively low temperatures of ~100 ºC and without vacuum equipment. Furthermore, the cell form factor can be modified depending on the underlying substrate, with many thin film solar cells being deposited on plastic substrates that are very flexible and lightweight. This design versatility opens a wide range of new and exciting application opportunities for thin film PV.

Solution-processability has helped accelerate thin film PV to market. Wireless headphones powered by dye sensitized solar cells (DSSCs) already exist and are available to purchase in shops.

The household brand Adidas has recently announced it is partnering with DSSC-manufacturer, Exeger, to make their own solar-powered headphones. In addition, organic solar cells developed by Epishine are being used on a small scale to power motion sensors and people counters. Appearing on the scene are also electronic shelf labels powered by perovskite solar cells. These have just been released for business-to-business sale by the Polish company Saule Technologies.

PV-Powered Electronics Eases Performance Metrics

Traditionally, efficiency and durability have been key metrics by which solar technology is judged. This is because mainstream applications such as rooftop and utility-scale PV benefit from the highest efficiency panels with lifespans >20 years. In contrast, high efficiency is not a strict requirement for emerging PV applications such as self-powered consumer electronics.

For example, powering headphones, sensors, and lights do not require high efficiency solar panel technology. Solar cells with efficiencies of 10-15% could be sufficient to operate most small and portable electronics. Durability is another typically important criterion that can be relaxed since many electronics are intended for short-term use, with consumers frequently updating their devices for newer models.

The key metric for the successful deployment of solar cells in consumer and retail electronics is cost. Given the increasingly high volume of consumer and retail electronics, energy solutions need to be economical, especially as solar technology will be competing with well-established and relatively inexpensive batteries. Solar could move into a competitive position with batteries if it were to demonstrate lower costs and greater practicality. Our analysis indicates that solution-processable PV is likely to be an important stimulus for the cost-competitive fabrication of thin film PV for self-powered electronics.

How Thin Film PV Can Improve Supply Chain Security

The conventional silicon photovoltaics market is worth over a hundred billion dollars with firmly established roots in the Asia Pacific region. The silicon market in recent years has experienced a substantial flux following political tensions and supply chain disruptions leading to concerns over global dependency on a monopolized commodity.

Since the COVID-19 pandemic, China’s silicon industry has been plagued by polysilicon supply shortages. This has extended lead times from just a few weeks prior to the pandemic to as long as one year currently. This has affected not only the PV sector but the wider semiconductor industry leading to a global chips shortage.

Reinventing the silicon industry is hard work and cost-competitive production of silicon is unlikely to appear soon in Europe and North America. On the other hand, the thin film solar landscape grants a clean slate to work with that could make sprawling supply chains and energy dependency a thing of the past. Furthermore, the diversification of the PV market through the development of alternatives to silicon will alleviate dependency on any one technology.

For the most part, the manufacturing of thin PV technology is not restricted to any specific geographic monopoly. There are companies worldwide, including in the UK, the US, Sweden, Poland, and China, that are developing thin film photovoltaics for a variety of different applications.

Due to the simpler manufacturing, more accessible materials, and smaller factory footprint requirements, thin film PV is far simpler to manufacture in-house with a greater degree of vertical integration and supply chain independence. Being able to deliver much needed renewable energy sources on a localized and regional scale is an advantage for supply chain security.

The thin film photovoltaics market is set to grow to US$6.1 billion by 2033, driven forward by growth within a range of application sectors, from utility-scale PV to self-powered electronics. For many thin film PV types, the synthesis is straight forward, and deposition can be carried out without the need for a vacuum or high temperatures. The possibility of creating flexible devices also opens up new applications that mainstream silicon PV cannot target due to its bulk, weight, and rigidity.