Versatile Device Architectures for High-Performing Light-Soaking-Free Inverted Polymer Solar Cells.

Area of Science:

• Materials Science
• Photovoltaics
• Organic Electronics

Background:

• Metal oxide charge transport layers are crucial for high-efficiency, long-lifetime inverted polymer solar cells.
• Low-temperature processed metal oxides, like TiO2, often suffer from intrinsic defects causing efficiency losses and light-soaking instability.
• Addressing these defects is key to unlocking the full potential of polymer solar cell technology.

Purpose of the Study:

• To investigate the impact of polyethyleneimine (PEI) and poly(9,9-bis(6'-(N,N-diethylamino)propyl)-fluorene-alt-9,9-bis-(3-ethyl(oxetane-3-ethyloxy)-hexyl)-fluorene] (PFN-OX) on low-temperature processed TiO2 electron transport layers (ETLs).
• To determine the effectiveness of these modifications in mitigating light-soaking issues in inverted polymer solar cells.
• To achieve stable, high-efficiency inverted polymer solar cells using modified ETLs.

Main Methods:

• Modification of low-temperature processed TiO2 ETLs with PEI and PFN-OX.
• Fabrication of inverted PTB7-Th:PC71BM solar cells incorporating the modified ETLs.
• Analysis of device performance, efficiency, and light-soaking stability.

Main Results:

• PEI modification effectively eliminated light-soaking issues in the TiO2 ETL due to the formation of abundant dipole moments.
• PFN-OX modification was ineffective in mitigating light-soaking, attributed to deficient dipole moments at the interface.
• PEI modification enabled versatile device architectures, yielding light-soaking-free inverted solar cells with over 10% efficiency.

Conclusions:

• PEI is a highly effective modifier for low-temperature processed TiO2 ETLs, significantly improving the stability of inverted polymer solar cells.
• The formation of dipole moments at the ETL interface is critical for preventing light-soaking degradation.
• PEI modification offers a promising strategy for developing stable and efficient next-generation polymer solar cells.