Progress
in dye-sensitized solar cells (DSSCs) has been benchmarked
with N719 dye-based devices. However, power conversion efficiency
(PCE) improvements performed in low-energy-performing devices cannot
be extrapolated to high-performing ones. This points to the need for
using a high PCE reference DSSC device, which preferably should be
possible for preparation using readily available commercial reactants
and parts. This study reports an optimized DSSC prepared with commercial
reactants, displaying a PCE of up to 9.84% under simulated solar light
and of 28.7% under artificial room light. The efficient light harvesting
in the photoanode and electron recombination suppression in the photoanode/electrolyte
interface were systematically optimized; the thickness and light-scattering
ability of the photoanode mesoporous layers were tuned to maximize
light harvesting and minimize the recombination losses. Electron back
recombination with electrolyte was minimized using a TiO2 blocking layer and treating the mesoporous layer of TiO2 with TiCl4. Finally, despite the use of a light-scattering
TiO2 coating over the mesoporous layer, the use of a light
reflection layer applied to the back of the devices proved to improve
the PCE further.
Due to the extremely high power conversion efficiency under indoor light, aesthetic appeal, and safety, the mature technology of dye-sensitized solar cells (DSSCs) is now considered as one of the most budding technologies to address the fast-growing need for cordless power in countless IoT devices and wireless sensors. The monolithic design of DSSCs (M-DSSCs) is technologically attractive for commercial production offering straightforward processing in-series modules, low cost, and compactness. The advancements in liquid-junction M-DSSCs reported so far are related only to conventional Ru-dye and I 3 − /I − electrolyte devices. The present study reports a M-DSSC incorporating a Co(III)/(II)(bpy) 3 redox shuttle and a YD2-o-C8 porphyrin dye and developed using commercial materials. The apparent activation energy for electron transfer, electron charge-transfer resistance, and exchange current density on FTO−Pt nanoparticles, Pt metal, graphite/carbon-black, and PEDOT:PSS in the cobalt electrolyte were determined to identify the favorable counter-electrode. The impact of the electrical spacer layers made from conventional ZrO 2 and highly reflective rutile TiO 2 on the photocurrent quantum yield was also assessed. The recombination-suppressing additive concentration in the electrolyte and photoanode sensitization conditions were thoroughly optimized to render M-DSSC devices with a photocurrent conversion efficiency of 9.5% under 1-sun illumination, which is by far the highest reported for M-DSSCs. The high power conversion efficiency of ca. 22% was attained under 1000 lx artificial light, making the developed M-DSSCs very attractive for indoor use.
Dye-sensitized solar cells (DSSCs) are among the leading PV technologies for indoor applications. These devices need to be optimized for these illumination conditions since, as it will be demonstrated, the best devices under solar conditions do not originate from the best devices under artificial illumination. This work studies the impact of the photoanode thickness, its light-scattering properties, dye loading, distance from the photoelectrode to the counter electrode on the charge transfer, recombination, and photovoltaic response of cobalt (III/II) bipyridine ([Co(bpy) 3 ] 3+/2+ ) and iodide/triiodide (I − /I 3 − ) DSSCs under 1 Sun and artificial 1000 lx light illumination. The champion [Co(bpy) 3 ] 3+/2+ device displayed a power conversion efficiency (PCE) of 11.0 and 32.0% under AM1.5G and 1000 lx, respectively. The best I − /I 3 − cells yielded 9.0% 1 Sun PCE and 23.1% of PCE under 1000 lx. Optimized [Co(bpy) 3 ] 3+/2+ and I − /I 3 − DSSCs demonstrated huge potential as efficient indoor-photovoltaics and can straightforwardly be used as back-illuminated devices to improve the output power under low illumination. Under 1000 lx room light, the champion cobalt DSSCs displayed a record PCE of 27.3% from the rear-side with 85.3% of retention ratio.
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