Triple-junction solar cells with improved carrier and photon management

Technical Deep Dive: Triple-Junction Solar Cells with Improved Carrier and Photon Management

Overview

• This work presents advances in perovskite-silicon triple-junction solar cells, which offer higher efficiency than dual-junction devices but require addressing key performance bottlenecks.
• The key innovations are:
  • A non-volatile additive that enhances the open-circuit voltage and stability of the wide-bandgap perovskite top cell.
  • A three-step deposition strategy to form thick, low-bandgap perovskite middle cells with superior microstructure and charge extraction.
  • Integration of low-refractive-index SiO₂ nanoparticles in the textured silicon bottom cell to improve optical absorption in the middle cell.
• These advancements combine to achieve a certified efficiency of 30.02% in 1 cm² perovskite-perovskite-silicon triple-junction devices.

Problem & Context

• Perovskite-silicon tandem solar cells offer efficiency gains over single-junction silicon, but adding a third perovskite subcell further boosts the theoretical efficiency limit.
• However, perovskite-perovskite-silicon triple-junctions face two key challenges:
  1. Lower open-circuit voltage (Voc) in the wide-bandgap perovskite top cell due to non-radiative recombination.
  2. Limited photocurrent generation in the middle perovskite subcell.

Methodology

• To address the Voc issue in the top cell:
  • Investigated the use of a non-volatile additive, 4-hydroxybenzylamine, to regulate perovskite crystallization and passivate defects.
  • Optimized energy-level alignment at interfaces to further improve Voc.
• To overcome the photocurrent limitation in the middle cell:
  • Developed a three-step deposition process to grow thick, low-bandgap perovskite films while preserving microstructural integrity.
  • Integrated low-refractive-index SiO₂ nanoparticles in the front valleys of the textured silicon bottom cell to act as an optical middle-reflector, enhancing light absorption in the middle cell.

Results

• The 4-hydroxybenzylamine additive enabled wide-bandgap perovskite top cells with Voc up to 1.405 V, a significant improvement over previous reports.
• The three-step middle cell deposition process yielded thick, high-quality perovskite layers with enhanced electron extraction.
• The SiO₂ nanoparticle optical middle-reflector improved current generation in the middle subcell.
• Combining these innovations, the authors fabricated 1 cm² perovskite-perovskite-silicon triple-junction solar cells with a certified efficiency of 30.02%.

Interpretation

• The enhancements to the top and middle subcells address two key bottlenecks in perovskite-perovskite-silicon triple-junctions.
• The additive-enabled wide-bandgap perovskite and the three-step middle cell deposition represent important advances in perovskite materials and processing.
• The optical middle-reflector is a creative approach to improving light management in the multilayer device structure.

Limitations & Uncertainties

• The source does not provide detailed performance metrics (e.g. Jsc, FF) for the individual subcells or the full device.
• The long-term stability of the devices is not assessed beyond the perovskite top cell.
• The generalizability of the materials and processing strategies to other perovskite compositions or tandem architectures is not discussed.

What Comes Next

• Further optimization of the perovskite compositions, interfaces, and device structures to push triple-junction efficiencies higher.
• Investigation of the scalability and reliability of the reported approaches for manufacturing-scale implementation.
• Exploration of additional light management techniques to enhance photon absorption and utilization across the triple-junction.

Sources:

• Triple-junction solar cells with improved carrier and photon management