Enhancing the Performances of P3HT:PCBM–MoS<sub>3</sub>‑Based H<sub>2</sub>‑Evolving Photocathodes
with Interfacial Layers
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Abstract
Organic semiconductors have great
potential for producing hydrogen in a durable and economically viable
manner because they rely on readily available materials and can be
solution-processed over large areas. With the objective of building
efficient hybrid organic–inorganic photoelectrochemical cells,
we combined a noble-metal-free and solution-processable catalyst for
proton reduction, MoS<sub>3</sub>, and a poly(3-hexylthiophene):phenyl-C<sub>61</sub>-butyric acid methyl ester (P3HT:PCBM) bulk heterojunction
(BHJ). Different interfacial layers were investigated to improve the
charge transfer between P3HT:PCBM and MoS<sub>3</sub>. Metallic Al/Ti
interfacial layers led to an increase of the photocurrent by up to
8 mA cm<sup>–2</sup> at reversible hydrogen electrode (RHE)
potential with a 0.6 V anodic shift of the H<sub>2</sub> evolution
reaction onset potential, a value close to the open-circuit potential
of the P3HT:PCBM solar cell. A 50-nm-thick C<sub>60</sub> layer also
works as an interfacial layer, with a current density reaching 1 mA
cm<sup>–2</sup> at the RHE potential. Moreover, two recently
highlighted figures-of-merit, measuring
the ratio of power saved, Φ<sub>saved,ideal</sub> and Φ<sub>saved,NPAC</sub>, were evaluated and discussed to compare the performances
of various photocathodes assessed in a three-electrode configuration.
Φ<sub>saved,ideal</sub> and Φ<sub>saved,NPAC</sub> use
the RHE and a nonphotoactive electrode with an identical catalyst
as the dark electrode, respectively. They provide different information
especially for differentiation of the roles of the photogenerating
layer and catalyst. The best results were obtained with the Al/Ti
metallic interlayer, with Φ<sub>saved,ideal</sub> and Φ<sub>saved,NPAC</sub> reaching 0.64% and 2.05%, respectively