5.4 Inverted and tandem device structures

Organic photovoltaics are evolving with new device architectures. Inverted structures flip electrode positions, boosting stability and efficiency. Tandem cells stack multiple layers to capture more sunlight, pushing power conversion to new heights.

These advanced designs come with challenges. Fabrication requires precise control and material compatibility. Researchers are developing optimization strategies, from interface modification to roll-to-roll processing, to unlock the full potential of these innovative solar cells.

Device Architectures in Organic Photovoltaics

Concept of inverted device architectures

Top images from around the web for Concept of inverted device architectures

• 

  Challenges and approaches towards upscaling the assembly of hybrid perovskite solar cells ... View original

  Is this image relevant?

• 

  Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original

  Is this image relevant?

• 

  Frontiers | Urea-Doped ZnO Films as the Electron Transport Layer for High Efficiency Inverted ... View original

  Is this image relevant?

• 

  Challenges and approaches towards upscaling the assembly of hybrid perovskite solar cells ... View original

  Is this image relevant?

• 

  Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original

  Is this image relevant?

1 of 3

Top images from around the web for Concept of inverted device architectures

• 

  Challenges and approaches towards upscaling the assembly of hybrid perovskite solar cells ... View original

  Is this image relevant?

• 

  Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original

  Is this image relevant?

• 

  Frontiers | Urea-Doped ZnO Films as the Electron Transport Layer for High Efficiency Inverted ... View original

  Is this image relevant?

• 

  Challenges and approaches towards upscaling the assembly of hybrid perovskite solar cells ... View original

  Is this image relevant?

• 

  Inverted organic photovoltaics with a solution-processed ZnO/MgO electron transport bilayer ... View original

  Is this image relevant?

1 of 3

• Inverted device structure reverses charge collection electrodes placing cathode on transparent substrate and anode on top
• Benefits include improved device stability, better compatibility with air-stable high work function metals (silver, gold), and enhanced charge collection efficiency
• Key components comprise electron transport layer (ETL) (zinc oxide, titanium dioxide), active layer (polymer:fullerene blend), and hole transport layer (HTL) (PEDOT:PSS, MoO3)
• Charge collection process involves electrons collected at bottom electrode and holes at top electrode, reducing charge recombination

Working principle of tandem cells

• Tandem cell structure stacks multiple subcells in series, each optimized for different parts of solar spectrum (visible, near-infrared)
• Working principle involves light absorption in multiple active layers, charge generation and separation in each subcell, and recombination layer between subcells facilitating charge transfer
• Advantages include increased overall power conversion efficiency, better utilization of solar spectrum, and reduced thermalization losses
• Types of tandem cells include two-terminal (2T) configuration with series-connected subcells and four-terminal (4T) configuration allowing independent operation of subcells

Fabrication challenges for advanced cells

• Inverted device fabrication requires careful selection of electron transport materials, optimization of layer thicknesses, and interface engineering between layers
• Tandem device fabrication demands precise control of multiple layer deposition, development of efficient recombination layers (metal oxides, ultrathin metals), and current matching between subcells
• Material compatibility issues arise from solvent orthogonality for solution processing and thermal stability during fabrication
• Scalability concerns involve maintaining uniformity over large areas and developing industrial-scale fabrication techniques (roll-to-roll processing)

Optimization strategies for device performance

• Inverted device optimization focuses on interface modification for improved charge extraction, development of new electron transport materials (metal oxides, conjugated polyelectrolytes), and optimization of active layer morphology
• Tandem device optimization involves subcell current matching through thickness adjustment, spectral complementarity of subcells, and transparent electrode development for intermediate layers (ITO, graphene)
• Advanced fabrication techniques include roll-to-roll processing for large-scale production and slot-die coating for uniform layer deposition
• Performance characterization utilizes external quantum efficiency (EQE) measurements and $J-V$ curve analysis under standard testing conditions (AM 1.5G, 100 mW/cm²)
• Stability enhancement employs encapsulation techniques (glass, flexible barriers) and development of intrinsically stable materials (fullerene-free acceptors, crosslinkable polymers)