Researchers at the Indian Institute of Technology (IIT) Bombay have successfully fabricated an inverted low-bandgap perovskite solar cell designed for integration in four-terminal (4T) perovskite-silicon tandem solar cells. This innovation marks a step forward in boosting the performance of next-generation photovoltaics.
Innovative p-i-n Device Architecture
Unlike conventional halide perovskite solar cells that follow an “n-i-p” structure, the new device adopts a “p-i-n” configuration. In this design, the hole-selective contact layer (p) is placed at the bottom, followed by an intrinsic perovskite absorber (i), and topped with the electron transport layer (n). This configuration enables illumination through the hole-transport layer (HTL), enhancing optical and electrical performance compared to traditional designs that receive light through the electron transport layer.
Optimized Interlayer Boosts Performance
To further enhance the cell’s efficiency, the research team introduced a passivating interlayer of aluminum oxide (Al₂O₃) using atomic layer deposition (ALD). “We used Al₂O₃ nanoparticles for interface passivation between the perovskite and the charge transport layer C₆₀,” said lead researcher Dinesh Kabra. The addition of a precisely optimized 3 nm-thick Al₂O₃ interlayer increased the cell efficiency from 17.09% to 19.16%. It also improved the fill factor from 71.44% to 77.36% compared to reference cells without the interlayer.
Layered Cell Configuration
The perovskite solar cell structure includes:
- A glass/indium tin oxide (ITO) substrate
- An HTL made of methyl-substituted carbazole (Me-4PACz)
- A perovskite absorber with a 1.67 eV bandgap
- The optimized Al₂O₃ interlayer
- A C₆₀-based ETL
- A bathocuproine (BCP) buffer
- A silver (Ag) metal electrode
Two devices were fabricated: one with a 0.175 cm² active area (efficiency: 18.77%) and another with a 1.08 cm² active area (efficiency: 16.92%).
High-Efficiency Tandem Integration
These perovskite cells were then paired with a silicon bottom cell (efficiency: 25.5%) to create a 4T tandem device. When tested under standard illumination:
- The tandem with the 0.175 cm² perovskite top cell achieved 29.14% efficiency
- The tandem with the 1.08 cm² top cell reached 26.86% efficiency
Looking Ahead: Optimizing for Future Gains
According to Kabra, the team sees strong potential for further improvements. “By adding an optical coupler between the top and bottom cells, we can enhance near-infrared (NIR) transmission, which could further elevate the performance of these tandem solar cells,” he explained. As reported by pv-magazine-india.com, the development places IIT Bombay at the forefront of tandem solar cell research and supports India’s broader push for high-efficiency, scalable renewable energy solutions.
