Bifunctional Compound Induced Dual Back Surface Fields for Efficient Hole Transport Layer-Free Perovskite Solar Cells

Area of Science:

• Materials Science
• Renewable Energy
• Photovoltaics

Background:

• Carbon-based hole transport layer-free (C-HTL-free) perovskite solar cells (PSCs) offer a pathway to low-cost and stable photovoltaics.
• The absence of a hole transport layer (HTL) in C-HTL-free PSCs typically leads to reduced power conversion efficiency (PCE) due to a lack of effective back surface field (BSF).

Purpose of the Study:

• To investigate the benefits of forming dual BSFs for improving the PCE of C-HTL-free PSCs.
• To introduce trityl tetrakis(pentafluorophenyl)borate (Tr+TPFB-) as a novel material for enabling dual BSFs in C-HTL-free PSCs via post-treatment.

Main Methods:

• Device simulation to explore the impact of dual BSFs on PSC performance.
• Post-treatment of C-HTL-free PSCs with Tr+TPFB- to induce dual BSF formation.
• Photoluminescence lifetime imaging to analyze photocarrier dynamics within the device cross-section.

Main Results:

• Dual BSFs were successfully formed in C-HTL-free PSCs using Tr+TPFB- post-treatment.
• TPFB- passivated n-doping defects in perovskite, creating an n-p homojunction.
• Tr+ extracted electrons from the carbon electrode, lowering its work function, thus establishing the dual BSFs.
• Improved photocarrier separation and extraction were observed, evidenced by photoluminescence lifetime imaging.
• A significant increase in average open-circuit voltage (Voc) of approximately 70 mV was achieved.

Conclusions:

• The introduction of dual BSFs via Tr+TPFB- post-treatment is an effective strategy to enhance the performance of C-HTL-free PSCs.
• This method addresses the limitations of HTL-free architectures by improving charge dynamics and device voltage.
• A champion PCE of 20.79% was obtained, demonstrating the potential of this approach for efficient and stable perovskite solar cells.