Industrializing Perovskite Tandems With ALD-Based Processing

Key takeaways:

• Leadmicro presented ALD-based equipment solutions aimed at scaling perovskite tandem manufacturing

• ALD can be used to improve encapsulation, transport layers, and interface stability in perovskite cells

• Combining ALD with laser processing helps reduce inactive module areas and improve overall power output

Over the last few years, perovskite tandem technology has progressed to the point that mainstream crystalline silicon players have invested in its research and also achieved record lab-scale efficiencies. However, researchers are still addressing several challenges intrinsic to the perovskite material, process optimizations for efficiency improvements, scalability, and reliability, before the technology can reach meaningful commercial scale.

Companies such as Oxford PV and LONGi have achieved record efficiencies, with the former reaching 28.6% and the latter 33% on large-area cells. These are just 2 examples of achievements across several institutes and companies. The small-area lab-scale efficiencies are even higher, recorded by institutes and also mainstream manufacturers across the globe.

At this point, it is important to industrialize this technology, which has significant potential in terms of power conversion efficiency. That is where companies like Leadmicro, which provides industrial manufacturing equipment, come into the picture. At the TaiyangNews Next-Generation PV Technology Conference, Jerry Liao, CTO of Leadmicro shared the company’s progress in this area.

Apart from efficiency, production cost and stability play a key role in the industrialization of any technology. There are stability issues for various layers of the perovskite cell. Humidity, oxygen, and temperature are problematic for the perovskite material, hole transport layer (HTL), and electron transport layer (ETL). Additionally, under certain conditions, metal atoms from the metal electrode layer diffuse into the perovskite layer and, conversely, the migration of ions from the core layer to the metal corrodes the metal electrode.

These problems can be addressed by optimizing layers, using additional buffer layers, and even encapsulation. All of these can be achieved using atomic layer deposition (ALD), which results in uniform, pinhole-free layers. While the use of ALD-TiO₂ was common practice previously, ALD-SnO₂ is now used for ETL deposition and to encapsulate the core layers, which act as a barrier to carrier diffusion and address ingress or diffusion issues. Earlier research also explored an ALD-AlO_x layer for encapsulation after the electrode layers are deposited, protecting the overall device. As a mature technology used in display manufacturing, it can also find relevant applications in perovskite technology. For HTL, NiO_x sputtering is currently used, but because it can cause damage, ALD can be an alternative route to deposit this layer.

Leadmicro is developing equipment for ALD solutions in perovskite manufacturing. The inline ALD tool, which typically produces CVD traces that lead to non-uniform layers, is now fully optimized, according to the results shared by Liao. Additionally, physical vapor deposition (PVD), laser processes, evaporation coating, and slot-die equipment are developed to be offered as turnkey solutions. The company offers key equipment specific to batch or inline processing, as well as a platform for processing flexible perovskite cells. Liao claims that Leadmicro can currently offer a 500 MW turnkey line for manufacturing perovskite on a substrate up to 1,200 × 2,400 mm, achieving efficiencies up to 19%.

Advantages of ALD, together with laser processes, include reducing the dead zone area. The dead zone corresponds to inactive areas that do not contribute to energy generation. For a module with a 1,200 x 2,400 mm area and a 250 µm dead zone per subcell, reducing the dead zone to 150 µm per subcell can increase power output by approximately 12 W, according to Liao.

Leadmicro’s current customers include perovskite tandem players and large-area single-junction perovskite makers with pilot lines installed and either in operation or in the commissioning process.