The combination of oxide and heavier chalcogenide layers
in thin film photovoltaics suffers limitations associated with oxygen
incorporation and sulfur deficiency in the chalcogenide layer or with
a chemical incompatibility which results in dewetting issues and defect
states at the interface. Here, we establish atomic layer deposition
(ALD) as a tool to overcome these limitations. ALD allows one to obtain
highly pure Sb2S3 light absorber layers, and
we exploit this technique to generate an additional interfacial layer
consisting of 1.5 nm ZnS. This ultrathin layer simultaneously resolves
dewetting and passivates defect states at the interface. We demonstrate
via transient absorption spectroscopy that interfacial electron recombination
is one order of magnitude slower at the ZnS-engineered interface than
hole recombination at the Sb2S3/P3HT interface.
The comparison of solar cells with and without oxide incorporation
in Sb2S3, with and without the ultrathin ZnS
interlayer, and with systematically varied Sb2S3 thickness provides a complete picture of the physical processes
at work in the devices.
A set of Pd(II) biladiene complexes bearing different combinations of methyl-and phenyl-substituents on the sp 3 -hybridized meso-carbon (the 10-position of the biladiene framework) was prepared and studied. In addition to a previously described Pd(II) biladiene complex bearing geminal dimethyl substituents a the 10-position (Pd[DMBil]), homologous Pd(II) biladienes bearing geminal methyl and phenyl substituents (Pd[MPBil1]) and geminal diphenyl groups-(Pd[DPBil1]) were prepared and structurally characterized. Detailed electrochemical as well as steady-state and time-resolved spectroscopic experiments were undertaken to evaluate the influence of the substituents on the biladiene's tetrahedral meso-carbon. Although all three biladiene homologues are isostructural, Pd[MPBil1] and Pd[DPBil1] display more intense absorption profiles that shift slightly toward lower energies as geminal methyl groups are replaced by phenyl rings. All three biladiene homologues support a triplet photochemistry, and replacement of the geminal dimethyl substituents of Pd[DMBil1] (Φ Δ = 54%) with phenyl groups improves the ability of Pd[MPBil1] (Φ Δ = 76%) and Pd[DPBil1] (Φ Δ = 66%) to sensitize 1 O 2 . Analysis of the excited-state dynamics of the Pd(II) biladienes by transient absorption spectroscopy shows that each complex supports a long-lived triplet excited-state (i.e., τ > 15 μs for each homologue) but that the ISC quantum yields (Φ T ) varied as a function of biladiene substitution. The observed trend in ISC efficiency matches that for singlet oxygen sensitization quantum yields (Φ Δ ) across the biladiene series considered in this work. The results of this study provide new insights to guide future development of biladiene based agents for PDT and other photochemical applications.
Bodipy-based donor–acceptor dyads were evaluated using transient absorption spectroscopy to reveal the influence of beta vs. meso substitution on excited-state dynamics.
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