Unmasking Donor–Acceptor Defect Tolerance and Doping Optima in a Phenazine Small-Molecule Organic Solar Cell via SCAPS-1D

Abstract

Phenazine-based small-molecule donors have recently emerged as promising candidates for organic solar cells (OSCs) owing to their planar, electron-deficient fused-ring cores and strong intermolecular π–π stacking. Building on a previously reported dibenzo[a,c]phenazine-based donor, SA1, paired with the fullerene acceptor PC₇₁BM, this study presents an independent, expanded SCAPS-1D sensitivity analysis of the ITO/PC₇₁BM/SA1/Pt planar heterojunction. Beyond the single-pass sequential optimization typically reported for such devices, the donor and acceptor layers were separately probed across thickness, bulk defect density, doping concentration, series and shunt resistance, electrode work function, and operating temperature. The results reveal a pronounced asymmetry in defect tolerance: the SA1 donor layer is essentially insensitive to bulk trap density up to 10¹⁸ cm⁻³, whereas the PC₇₁BM acceptor layer’s defect density is the dominant loss channel, degrading power conversion efficiency (PCE) from 5.72% to 0.33% and inducing S-shaped J–V distortions at high trap densities. A non-monotonic acceptor-doping optimum near 10¹⁶ cm⁻³ raised PCE to 6.72%, exceeding the literature baseline. Shunt resistance was found to be far more performance-limiting than series resistance, and the front (ITO) electrode work function was identified as the single most sensitive contact parameter, while the back (Pt) contact and operating temperature (up to 420 K) showed negligible-to-favorable effects. These findings identify a joint-optimization pathway — combining a thicker acceptor layer, reduced doping, and a low-defect interface — that was left unexplored by prior sequential optimization, providing practical design guidance for phenazine-based small-molecule OSCs.