Ultrafast Spectroscopic Identification of Hole Transfer in All-Polymer Blend Films of Poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b:4,5-b′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione) and Poly[1,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)]

5 years ago

Ultrafast Spectroscopic Identification of Hole Transfer in All-Polymer Blend Films of Poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b:4,5-b′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione) and Poly[1,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)]

Chuanxiang Sheng, Haibin Zhao, Wanli Ma, Yalong Xu, Lu Han, Feng Jin, Wenping Guo, Jianyu Yuan

All-polymer solar cells composed of wide-band-gap polymer poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2-b:4,5-b′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione) (PTP8) as the donor and poly[1,8-bis(dicarboximide)-2,6-diyl]-alt-5,5′-(2,2′-bithiophene)] [P(NDI2OD-T2), also known as Activink N2200] as the acceptor exhibit a broad absorbance in the range 300–900 nm, thanks to complementary absorption of near-infrared light by N2200. Although N2200 shows reasonably high electron mobility, the contribution of the photogenerated excitons in N2200 to the power conversion of the PTP8/N2200 solar cell is insignificant. Here, the hole transfer from N2200 to PTP8 in PTP8/N2200 blend films was investigated by utilizing ultrafast transient absorption spectroscopy. The spectral fingerprints of ground-state bleaching and hole polaron-induced absorption of PTP8 are identified under selective excitation of the N2200 component and unambiguously indicate hole transfer from N2200 to PTP8. The hole transfer is slow (∼100 ps), comparable to the geminate exciton recombination rate, consequently limiting the transfer efficiency and carrier generation. The hole-transfer efficiency depends on the PTP8/N2200 weight ratio, showing a highest value of ∼14.1% in the 3:2 film.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b04984

DOI: 10.1021/acs.jpcc.7b04984