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.

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Dye-sensitized solar cells (DSSCs) emerged in the market as one of the most promising indoor photovoltaic technologies to address the need for wireless powering of low-consuming electronics and sensor nodes of the internet of things (IoT). The monolithic design structure of the cell (M-DSSCs) makes the devices simpler and cheaper, and it is straightforward for constructing in-series modules. The most efficient DSSCs reported so far are Co­(III/II)-mediated liquid junction cells with acetonitrile electrolytes; however, they are mostly unstable. This study reports on highly stable cobalt-mediated M-DSSCs, passing thermal cycling tests up to 85 °C according to ISOS standard protocols. Under 1000 h of aging in the dark and under simulated solar and artificial light soaking, all tested cells improved or retained their initial power conversion efficiency. Advanced long-term stability was achieved by eliminating the extrinsic factors of degradation, such as the interaction of the cell components with the environment and electrolyte leakage. This was obtained by encapsulation of the devices using a glass-frit sealant, including the holes for filling up the liquid components of the cells. The hermeticity of the encapsulation complies with the MIL-STD-883 standard fine helium gas leakage test, and its hermeticity remained unchanged after humidity–freeze cycles according to IEC 61646. The elimination of extrinsic degradation factors allowed reliable assessment of inner factors accountable for aging. The impact of the ISOS-protocol test conditions on the intrinsic device stability and long-term photovoltaic history of the M-DSSCs is discussed.

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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.