IIT Bombay’s 4T Silicon-Perovskite Tandem Solar Cell Hits 26% Efficiency

IIT Bombay’s 4T Silicon-Perovskite Tandem Solar Cell Hits 26% Efficiency

The Indian Institute of Technology, Bombay (IIT-B) has conducted one of the first experimental demonstrations of a 4T silicon-perovskite tandem solar cell, achieving over 26% efficiency. A team at the National Centre for Photovoltaic Research and Education (NCPRE) at IIT Bombay fabricated a semi-transparent perovskite solar cell (PSC), which, when combined with a silicon-based solar cell, demonstrated this high efficiency. A 4T tandem device, features four terminals, two for each layer of the tandem structure. This design allows for precise performance measurements, improved efficiency, and increased device longevity.

The research found that, although solar panel prices have dropped in recent years, there is still a need for more affordable solar energy solutions to make solar power truly ubiquitous. This is where perovskite solar cells (PSCs) come in, offering an alternative to traditional silicon solar cells due to their low fabrication costs and high efficiency.

Perovskite-Silicon Tandem Solar Cells

Perovskites refer to materials with a specific crystal structure, typically represented as ABX₃, where A, B, and X can be atoms or molecules, such as calcium titanium oxide (CaTiO₃). Perovskite solar cells (PSCs) have gained attention since 2009 when the first PSC was fabricated. These cells are highly efficient at converting light into electricity and are cost-effective to produce. However, they lack the stability of conventional silicon solar cells and tend to degrade when exposed to light, heat, or applied voltage for extended periods.

The team at IIT Bombay addressed this stability issue by integrating their PSC with a silicon solar cell in a tandem configuration. This combination enables the device to convert more light into electricity while also enhancing its stability and reducing overall lifetime costs.

Study Findings

For their study, the team first fabricated a thin-film perovskite solar cell, which is transparent to near-infrared (NIR) light. This transparency makes PSCs useful in applications such as building-integrated photovoltaics (BIPV) and vehicle-integrated photovoltaics (VIPV). The researchers then measured the power conversion efficiency (PCE), which indicates how much light is converted into electricity. The PSC recorded high efficiencies of 17.1% for a small-area (0.175 cm²) PSC and 16% for a large-area (0.805 cm²) PSC.

However, PSCs are still less stable than conventional silicon solar cells. To address this, the researchers used a tandem device architecture, layering the PSC on top of a commercially available Passivated Emitter and Rear Contact (PERC) silicon solar cell.

Although the PSC layer may degrade faster than the silicon layer, the fabrication process allows for easy replacement of the PSC without affecting the entire device. “In our case, i.e., in the 4T tandem configuration, when the top low-cost perovskite solar cell fails, it can be replaced with a new one because our tandem device is only optically coupled. This enhances the overall device lifetime,” explains Dinesh Kabra.

More importantly, the tandem device architecture also helps reduce the levelized cost of energy (LCOE) for tandem solar cells. LCOE measures the cost of electricity generation across different energy sources, and reducing it makes tandem solar cells more commercially viable.