Effect of Mixed Fullerene Ratio on the Optical and Electrical Properties of P3HT: ICxA Bulk Heterojunction Thin Films and Optical Modelling of OPV Devices.

Abstract

A series of P3HT: ICxA BHJ thin films was prepared with different donor–acceptor ratios to assess the influence of fullerene concentration on the optical and electrical properties of the active layer. Six acceptor ratios were considered (1:0.5, 1:0.8, 1:1, 1:1.2, 1:1.5 and 1:2) in this article. The topography of the surface was examined by capturing the AFM images, which confirmed that all samples exhibited an RMS of roughness (2~4 nm). The optical measurements of P3HT: ICxA revealed that the blending ratio (1:1.2) exhibited the highest optical response in comparison with other samples. For all films, the absorption coefficient satisfied α > 10⁴ cm⁻¹, indicating the occurrence of direct electronic transitions within the active layer. Electrical measurements as a function of sample temperature were demonstrated in the range of (25- 65 ^oC) at dark and light conditions. A photoactive layer, P3HT: ICxA, generates relatively similar values of current in both heating and cooling cycles, that suggested active layer morphology optimized and remained well-ordered throughout the thermal process. Finally, optical modelling of a complete OPV device was performed, and its results supported and confirmed the trends observed in both the optical and electrical measurements.