2 research outputs found
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‑<i>b</i>:4,5‑<i>b</i>′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)‑4<i>H</i>‑thieno[3,4‑<i>c</i>]pyrrole-4,6(5<i>H</i>)‑dione) and Poly[1,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)]
All-polymer
solar cells composed of wide-band-gap polymer polyÂ(1-{4,8-bisÂ[5-(2-ethylhexyl)Âthiophen-2-yl]-benzoÂ[1,2-<i>b</i>:4,5-<i>b</i>′]Âdithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4<i>H</i>-thienoÂ[3,4-<i>c</i>]Âpyrrole-4,6Â(5<i>H</i>)-dione) (PTP8) as the donor and polyÂ[1,8-bisÂ(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)] [PÂ(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
Thermal Annealing Effect on Ultrafast Charge Transfer in All-Polymer Solar Cells with a Non-Fullerene Acceptor N2200
Ultrafast transient absorption (TA)
spectroscopy was employed to
investigate the thermal annealing effect on the charge transfer (CT)
in bulk heterojunction (BHJ) all-polymer solar cells (all-PSCs) utilizing
an n-type polymer PÂ(NDI2OD-T2) (Polyera, N2200) as acceptor and a
low bandgap polymer PBPT as donor. The CT generates hole polarons
residing in the PBPT and electron polarons belonging to N2200, manifested
in the TA spectra of the BHJ films as the long-lived absorption peak
centered at ∼850 nm. The CT is most efficient in the film annealed
at 160 °C and its efficiency declines monotonically when enhancing
or reducing the annealing temperature, displaying a positive correlation
with the power conversion efficiency (PCE) of the corresponding solar
cell devices. This correlation is analyzed in terms of the crystallinity
and phase separation, which are the key factors determining the performance
of all-PSCs. Our results can provide valuable guidance for the fabrication
of BHJ all-PSCs to improve their PCE