Coumarin-Based Volatile and Non-Volatile Solid Additives Enable Organic Solar Cells with 20.32% Efficiency.

Area of Science:

• Materials Science
• Organic Electronics
• Photovoltaics

Background:

• Solid additives are crucial for improving organic solar cell (OSC) performance.
• Non-volatile solid (non-VS) additives offer convenient post-treatment but often underperform volatile solid (VS) additives in morphology optimization.
• A lack of systematic comparison exists regarding the working mechanisms of VS and non-VS additives in OSCs.

Purpose of the Study:

• To design and synthesize coumarin-derived volatile (C5) and non-volatile (C6) additives.
• To assess the impact of C5 and C6 on OSC device performance and morphology.
• To elucidate the distinct working mechanisms of non-VS and VS additives in OSCs.

Main Methods:

• Synthesis of coumarin-derived additives C5 (volatile) and C6 (non-volatile).
• Fabrication and characterization of organic solar cells (OSCs) with and without additives.
• Analysis of device morphology, charge transfer, energy loss, and exciton utilization.

Main Results:

• Both C5 and C6 additives optimized OSC morphology, improved charge transfer, and reduced energy loss compared to additive-free devices.
• The non-volatile additive C6 facilitated an additional charge transport pathway and enhanced exciton utilization via Förster-Resonance Energy Transfer (FRET).
• OSCs treated with C6 achieved a record power conversion efficiency (PCE) of 20.32%, outperforming additive-free (18.85%) and C5-treated (19.55%) devices.

Conclusions:

• Non-volatile solid additives, exemplified by C6, can effectively enhance OSC performance through improved morphology and charge transport mechanisms.
• C6 demonstrates superior performance as a small molecule non-VS additive, setting a new benchmark for OSC efficiency.
• This study provides critical insights into the differential mechanisms of VS and non-VS additives in boosting OSC photovoltaic performance.