Ultrafast and slow charge recombination dynamics of diketopyrrolopyrrole–NiO dye sensitized solar cells
2016 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 18, 18515-18527 p.Article in journal (Refereed) Published
In a photophysical study, two diketopyrrolopyrrole (DPP)-based sensitizers functionalized with4-thiophenecarboxylic acid as an anchoring group and a bromo (DPPBr) or dicyanovinyl (DPPCN2)group, and a dyad consisting of a DPP unit linked to a naphthalenediimide group (DPP–NDI), wereinvestigated both in solution and grafted on mesoporous NiO films. Femtosecond transient absorptionmeasurements indicate that ultrafast hole injection occurred predominantly on a timescale of B200 fs,whereas the subsequent charge recombination occurred on a surprisingly wide range of timescales,from tens of ps to tens of ms; this kinetic heterogeneity is much greater than is typically observed fordye-sensitized TiO2 or ZnO. Also, in contrast to what is typically observed for dye-sensitized TiO2, therewas no significant dependence on the excitation power of the recombination kinetics, which can beexplained by the hole density being comparatively higher near the valence band of NiO beforeexcitation. The additional acceptor group in DPP–NDI provided a rapid electron shift and stabilizedcharge separation up to the ms timescale. This enabled efficient (B95%) regeneration of NDI bya CoIII(dtb)3 electrolyte (dtb = 4,40-di-tert-butyl-2,20-bipyridine), according to transient absorptionmeasurements. The regeneration of DPPBr and DPPCN2 by CoIII(dtb)3 was instead inefficient, as mostrecombination for these dyes occurred on the sub-ns timescale. The transient spectroscopy data thuscorroborated the trend of the published photovoltaic properties of dye-sensitized solar cells (DSSCs)based on these dyes on mesoporous NiO, and show the potential of a design strategy with a secondaryacceptor bound to the dye. The study identifies rapid initial recombination between the dye and NiO asthe main obstacle to obtaining high efficiencies in NiO-based DSSCs; these recombination componentsmay be overlooked when studies are conducted using only methods with ns resolution or slower.
Place, publisher, year, edition, pages
2016. Vol. 18, 18515-18527 p.
Ultrafast, pDSSCs, Charge recombination
Research subject Chemistry with specialization in Physical Chemistry
IdentifiersURN: urn:nbn:se:uu:diva-300147DOI: 10.1039/c6cp01762bISI: 000379486200081PubMedID: 27338174OAI: oai:DiVA.org:uu-300147DiVA: diva2:950875
FunderSwedish Energy AgencyKnut and Alice Wallenberg Foundation