Improvement of bulk heterojunction organic solar cells based on PTB7:PC₆₁BM with small amounts of P3HT

Abstract

The effect of a small amount of poly(3-hexylthiophene) (P3HT) additive on the performance of bulk heterojunction (BHJ) organic solar cells based on poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]]:[6,6]-phenyl-C61-butyric acid methyl ester (PTB7:PC61BM) was investigated. The optimized solar cell with 5% P3HT weight fraction showed a marked improvement, with an open-circuit voltage of 0.76 V, a short-circuit current density of 17 mA/cm2, a fill factor of 0.40, and a power conversion efficiency of 5.11%. A notable reduction in the domain sizes of the active layers with 5% P3HT weight fraction was observed by atomic force microscopy. This suggests that the interface area between the PTB7 and PC61BM domains increased, resulting in an enhanced exciton dissociation. This also suggests that the small amount of P3HT in the PTB7:PC61BM active layer acted as a mediator to enhance the hole current from PTB7 domains to the poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) anode buffer layer. Possible mechanisms for these phenomena are discussed on the basis of the results of surface energy analysis.

Bulk-heterojunction Solar Cells Based on Ternary Blend Active Layers of PTB7, PC₆₁BM, and PC₇₁BM

“…2. The solar cells were fabricated based on the procedures previously described [32,33,37]. The devices were fabricated on an ITO-coated glass substrate with a sheet resistance of 10 Ω/sq (Techno Print) and a thickness of 150 nm with electrode patterns.…”

Enhanced Vertical Charge Transport of Homo‐ and Blended Semiconducting Polymers by Nanoconfinement

“…Our novel approach is also applicable and beneficial for polymer blends which are structurally incompatible. Lots of studies have been performed to use blends of multidonor materials to use wide range of light absorption by blending low‐bandgap and middle‐bandgap polymers . However, only a few combinations of polymers were available because structural and solvent compatibility between polymers is required.…”

“…However, only a few combinations of polymers were available because structural and solvent compatibility between polymers is required. Blends of P3HT and PTB7‐th show disrupted morphology having less crystalline structures due to their different chemical structures and chain orientation in the film states . However, our novel approach allows to process blends regardless of their compositions.…”

“…It was known that blending of semicrystalline and amorphous polymers typically leads to worse structural and electrical properties than those of individual polymers because of their structural incompatibility, which originated from the different intrinsic chemical structures. Several studies have shown that adding ternary components, P3HT, more than 10% into PTB7‐th/PCBM blends lead to deteriorated performance because of their different intrinsic chemical structures and chain orientation in thin film states . This structural incompatibility between two polymers could be overcome by our approach.…”

“…Lots of studies have been performed to use blends of multidonor materials to use wide range of light absorption by blending lowbandgap and middle-bandgap polymers. [38][39][40][41][42][43] However, only a few combinations of polymers were available because structural and solvent compatibility between polymers is required. Blends of P3HT and PTB7-th show disrupted morphology having less crystalline structures due to their different chemical structures and chain orientation in the film states.…”