Unveiling the Microscopic Origin of Non-Radiative Voltage Loss in Organic Solar Cells through a Controlled...

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Non-radiative voltage loss (ΔVnr) significantly limits organic solar cell (OSC) efficiency.
• The microscopic origins of ΔVnr are poorly understood due to complex bulk heterojunction morphologies.

Purpose of the Study:

• To elucidate the microscopic mechanisms behind non-radiative voltage loss in OSCs.
• To establish intrinsic relationships between interfacial characteristics, material properties, and device performance.
• To develop a general strategy for suppressing ΔVnr in next-generation OSCs.

Main Methods:

• Designed a triple-layer device architecture to independently control donor/acceptor (D/A) interface density.
• Decoupled interfacial properties, material parameters, and device performance for direct analysis.
• Correlated Urbach energy (EU), activation energy, and ΔVnr to understand voltage loss origins.

Main Results:

• ΔVnr arises from both carrier lifetime effects and thermodynamic redistribution between locally excited (LE) and charge-transfer (CT) states.
• Increased D/A interface density broadens excitonic states, lowers LE-to-CT conversion energy, and enhances non-radiative CT recombination.
• Demonstrated strong correlations between EU, activation energy, and ΔVnr, identifying them as critical factors in voltage loss.

Conclusions:

• Clarified the microscopic mechanisms governing non-radiative voltage loss in OSCs.
• Identified thermodynamic redistribution between LE and CT states as a key contributor to ΔVnr.
• Proposed a device design strategy to suppress ΔVnr and enhance OSC efficiency.