(Invited) Long Term Stability of Antimony Sulfide-Based Hybrid Solar Cells
Authors: Hayakawa Akinobu , Sagawa Takashi 
Published: February 2020

Recently various materials such as antimony sulfide (Sb2S3),1,2) antimony selenide,3) lead sulfide,4) cadmium selenide,5) lead-halogen perovskite6-8) 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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