Is Production of Perovskite-Silicon Solar Cells Scalable?

Today’s solar cells represent decades of efficiency improvements. The first silicon cell was demonstrated in the 1950s with just 5% efficiency, but 2022 saw that record jump to 26.8%. Meanwhile, companies and researchers have introduced new materials and designs offering higher performance, such as tandem solar cells made of perovskite and silicon. 

 

Tandem solar cell using perovskite and silicon. Image used courtesy of HZB

 

However, some of the materials and processing approaches used in tandem demonstrations are not conducive to terawatt (TW)-scale mass production. The world surpassed 1 TW of solar capacity in 2022, according to Solar Power Europe, and projections eye significant growth in the coming years. Keeping pace with demand may require adjusting the design and processing capabilities of high-performing, next-generation solar technologies. 

A study in Energy and Environmental Science notes that today’s perovskite-silicon tandem solar cells will need to be redesigned for large-scale manufacturing and reduced levelized cost of energy (LCOE). A multi-TW production landscape imposes additional constraints on the processing and sustainability of the materials used in tandems, factors that influence the overall cell design. 

 

What Are Tandem Solar Cells?

Multi-junction solar cells are connected in a series to absorb multiple wavelengths in the solar spectrum. This enables a superior module design that turns sunlight into electricity with record performance, surpassing the 30% efficiency threshold. 

Tandem solar panels consist of two solar subcells stacked on top of each other. The top cell, made of perovskite to collect high-energy photons, converts a portion of the solar spectrum into electricity and transmits light to the silicon base cell on the bottom, which collects lower-energy photons. 

This architecture offers a significant performance boost. Earlier this year, Saudi Arabia-based King Abdullah University of Science and Technology (KAUST) reached a power conversion efficiency of 33.7%. Comparatively, single-junction silicon solar cells have a theoretical efficiency limit of 29.4%, according to a 2022 study that developed a new model to assess this metric. 

 

Scaled Manufacturing Necessitates Material, Design Adjustments 

In the study, researchers at the University of Oxford and the Commonwealth Scientific and Industrial Research Organization in Australia discussed the need to redesign tandem cells with new and more abundant materials. 

Nearly all tandem solar cells are silicon heterojunction cells, which require more silver indium than other designs. Indium is a rare resource, while silver is subject to immense demand pressures. According to the Silver Institute, all major silver demand segments reached record highs in 2022, with the global total growing by 38% since 2020. 

The researchers stressed that current cell designs cannot sustain a future TW-capacity solar PV market. That means exploring indium alternatives and designs that don’t require as much silver content. 

One example discussed in the study is the industry-mainstay PERC, a modified version of silicon solar cells with an extra layer on the back. This design doesn’t require indium and uses less silver than silicon heterojunction (SHJ) and tunnel oxide passivated contact (TOPCon) cells. Adjusting the design requirements for a tandem architecture can narrow the efficiency gap compared to SHJ.

 

Summary of design considerations for the silicon bottom cell in tandem designs. Image used courtesy of the authors (Figure 12) – Creative Commons-BY license

 

More specifically, the researchers outlined a few design considerations for the bottom cell in a 2T silicon-based tandem, approaches that differ from that of a single junction silicon cell. 

1. Changes to the front surface: In addition to maximizing absorption and carrier collection, the front surface should accommodate the top cell fabrication. This could involve making adjustments to surface texturing. 

2. Electrical contact: An electrical interconnection between the top and bottom cells could be formed through local interconnections or a full area contact with one dimensional carrier transport.

3. Metalization: Forming metal contacts within the temperature limits of the top cell is a challenge. The authors stressed the need for solutions that reduce resistive losses in large-area devices.