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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