Abstract:
Polymer solar cells based on the bulk heterojunction structure have recorded remarkable improvements in their performance over the past
few years. They have elicited considerable research interest in recent years because they have a higher potential to promote low-cost, environ mentally friendly, non-complex, and flexible large-area devices compared to their inorganic counterparts. In this study, different films of the
organic polymer P3HT (poly-(3-hexylthiophene-2,5-diyl)) mixed with fullerene acceptors PC71BM ([6,6]-phenyl C71 butyric acid methyl
ester, mixture of isomers) and non-fullerene acceptors (NFAs) IEICO-4F (2,20
-[[4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno[1,2-
b:5,6-b0
]dithiophene-2,7-diyl]bis[[4-[(2-ethylhexyl)oxy]-5,2-thiophenediyl]methylidyne(5,6-difluoro-3-oxo-1H-indene-2,1(3H)-diylidene)]]
bis[propanedinitrile]), and COi8DFIC (2,2-[[4,4,11,11-tetrakis(4-hexylphenyl)-4,11-dihydrothieno [2,3:4,5]thieno [2,3d]thieno[2,3:4,5]-
thieno[2,3:4,5] pyrano[2,3:4,5]thieno[2,3:4,5] thieno[3,2-b]pyran-2,9-diyl]bis[methylidyne(5,6-difluoro)) were fabricated on glass substrates.
Ultraviolet–visible–near-infrared (UV–VIS–NIR), and photoluminescence (PL) characterizations were performed to determine the optical
properties and eventual analysis of the structural (H- and J-aggregation) differences in the blends, while atomic force microscopy was used
to analyze the surface morphologies of the polymer blends. The results of ultraviolet–visible–near infrared spectroscopy depicted better light
harvesting capabilities in non-fullerene acceptor based polymer blends of P3HT:COi8DFIC and P3HT:IEICO-4F, which had wider absorp tion spectra, indicating a larger absorption window and higher absorption intensities extending from NIR (near infrared) to the ultraviolet
(UV) region compared to P3HT:PC71BM blends, which had narrower absorption windows and lower absorption intensities. P3HT-fuller ene-based blends depicted a blue-shifted spectra, a characteristic of H-aggregates, while the NFA-based blends depicted red-shifted vibronic
structures, a characteristic of J-aggregates. There was lower PL intensities of the non-fullerene based blends compared to the fullerene-based
polymer blends, depicting more charge carrier recombination in fullerene-based polymer blends. These implied that the fullerene-based
blend had lower power conversion efficiency compared to non-fullerene-based blends
