Enhancing the Efficiency and Operational Stability of P3OT:PCBM Organic Solar Cells via Additive Engineering

Abstract

This paper addresses the fundamental challenges of efficiency and temporal stability in poly(3-octylthiophene) (P3OT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM)-based organic solar cells, which often suffer from instability in the active-layer micromorphology under operating conditions. A comparative study of three additive classes with different physical states was conducted: a high-boiling solvent (1,8-diiodooctane, DIO), a solid organometallic additive (ferrocene, Fc), and a polymeric additive (polyethylene glycol, PEG). Optical (UV–Vis), structural (XRD, Raman), and morphological (atomic force microscopy) characterizations reveal that each additive regulates film formation through a distinct mechanism. DIO slows solvent evaporation and promotes refined nanophase separation and enhanced ordering; Fc induces nucleation-driven ordering; and PEG smooths the surface and suppresses defects. These effects translate into improved photovoltaic performance, particularly in short-circuit current density and fill factor. The DIO-treated device achieved the highest power conversion efficiency (3.33%) compared to 1.93% for the reference device. Aging studies further demonstrate that solid and polymeric additives provide superior resistance to thermal and photo-induced degradation compared to solvent-treated devices. These findings highlight that selecting an appropriate additive class is an effective strategy to simultaneously enhance efficiency and long-term stability in P3OT:PCBM organic solar cells.