Novel Diffusion-Regulated Layering Methodology to Improve Blend Miscibility and Thermal Stability of Organic Photovoltaics

Extensive research on bulk-heterojunction (BHJ) optimization has advanced organic photovoltaics (OPVs). However, the need for research addressing the issue of morphological instability and ensuring long-term durability remains a priority. Herein, a diffusion-governed morphological modification methodology via a sequential deposition (SD) process comprising ternary components with low miscibility is demonstrated. Sequential coating of a high glass transition temperature (T_g) material and a host binary blend induces a concentration difference between successively coated layers, allowing for effective blending of immiscible materials during solvent evaporation. The enhanced miscibility of the SD-processed BHJ layer facilitates molecular interactions between the high T_g material and the host materials, thereby increasing the T_g of the BHJ blend. The SD-processed OPVs exhibit superior photovoltaic performance and suppressed glass transition under thermal stress compared to reference OPVs fabricated via a conventional method. After 500 h of thermal aging at 85 °C, the SD-BHJ OPV retains over 80% of its initial efficiency, whereas the reference device shows a drastic drop to below 80% of its initial efficiency after only 80 h. This study provides a step toward efficient, long-term stable OPVs by overcoming the limitations of blend miscibility and poor thermal durability of conventional BHJ systems via a SD process.