Recently various materials such as antimony sulfide (Sb₂S₃),^1,2) antimony selenide,³⁾ lead sulfide,⁴⁾ cadmium selenide,⁵⁾ lead-halogen perovskite^6-8) have been applied for organic-inorganic hybrid solar cells. Among these materials, Sb₂S₃ has much attraction for photovoltaics in terms of appropriate bandgap, high absorption coefficient, low toxicity, and abundance. Sb₂S₃ has been prepared by chemical bath deposition, atomic layer deposition, complex-decomposition method, and so on and applied as the thin film for solar cell, which has been attained the power conversion efficiency (PCE) of 7.5%.¹⁾ Although Sb₂S₃-based solar cell seems to be stable in air,²⁾ stability test under the accelerated conditions has not yet been reported. In addition, various materials such as SnO₂, TiO₂, or ZnO have been utilized as an electron transporting layer (ETL) and polythiophenes, 2,2’,7,7’-tetrakis(N,N-di-p-methoxyphenylamine)-9,9’-spirobifluorene, ZnPc, CuSCN, MoO₃, or NiO have been used as a hole transporting layer (HTL) of the Sb₂S₃ based solar cells, however, optimization of the combinations of ETL and HTL in terms of the durability has also not yet been explored. In this context, we prepared Sb₂S₃-based solar cells with TiO₂ or ZnO nanoparticles for ETL in addition to poly(3-hexylthiophene)-2,5-diyl (P3HT)/ (3, 4-ethylenedioxythiophene) : poly(styrene sulfonate) (PEDOT : PSS), ZnPc, or MoO₃ for HTL and compared their photovoltaic properties with encapsulation by using glass and UV cut-off films under JIS C8938 conditions of 1 sun at 63 °C at a relative humidity (RH) of 50%.

Among these hybrid solar cells, combination with ZnPc and TiO₂ has the highest durability with keeping the relative power conversion efficiency of 90% after the stability test under 1 sun at 63 °C at a RH of 50% for 500 h. In order to investigate the effect of UV light irradiation, another durability test of glass-ITO/TiO₂/Sb₂S₃/ZnPC/Au without UV cut filter was performed The photovoltaic performance was completely maintained for 3 d with UV cut filter, however it has almost been lost without the cut filter after 3 d. Decolorization was observed after the irradiation without the UV cut filter though the decolorization did not occur with the filter. Once the TiO₂ layer was removed from the cell, described as glass-ITO/ Sb₂S₃/ZnPC/Au, there was no decolorization even when without using the UV cut filter. In this context, anatase TiO₂ nanoparticles in this case act as the photocatalyst during the UV light irradiation to oxidize and decompose Sb₂S₃, which resulted in the above decolorization of the cells. Therefore, effective suppression of the photoactivation of TiO₂ through UV light irradiation by using cut filter is essential to realize the long term stability and promising further extension for optimization of the photovoltaic performance.

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