Enhancement of ternary blend organic solar cell efficiency using PTB7 as a sensitizer

Highlight
• The ternary structure can overcome the limitation of binary blend OPV devices.
• PTB7 works as a sensitizer and greatly enhances the optical performance.
• Carrier mobility was greatly enhanced and balanced charge transport was achieved.
• Using the ternary system with PTB7 significantly improves the device performance.

We demonstrate a significant improvement of power conversion efficiency (PCE) by the addition of the polymer 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] thio-phenediyl]] (PTB7) to a Poly[2,1,3-benzothiadiazole-4,7-diyl [4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2,6-diyl]] (PCPDTBT) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) host system, to form a ternary blend bulk heterojunction solar cell. This is the first reported investigation using PTB7 in a ternary system. The PTB7 concentration was varied from 1 to 9 wt% in the host system. In this ternary blend system, PTB7 works as a sensitizer and greatly enhances the optical performance. We demonstrate that positive charge from PCPDTBT is transferred to PTB7, which acts as an efficient charge transport matrix. The addition of 5 wt% PTB7 caused the highest improvement of average PCE, 28%, with reference to the binary PCPDTBT:PC71BM cell. The improved device performance is related to both the sensitized response over a large wavelength region and improved charge carrier transport.