Browsing by Author "Chen, C"

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    Antiferroelectric-to-Ferroelectric Switching in CH3NH3PbI3 Perovskite and Its Potential Role in Effective Charge Separation in Perovskite Solar Cells
    (American Physical Society, 2016) Sewvandi, GA; Hu, D; Chen, C; Ma, H; Kusunose, T; Tanaka, Y; Nakanishi, S; Feng, Q
    Perovskite solar cells (PSCs) often suffer from large performance variations which impede to define a clear charge-transfer mechanism. Ferroelectric polarization is measured numerically using CH3NH3PbI3 (MAPbI3) pellets to overcome the measurement issues such as pinholes and low uniformity of thickness, etc., with MAPbI3 thin films. MAPbI3 perovskite is an antiferroelectric semiconductor which is different from typical semiconducting materials and ferroelectric materials. The effect of polarization carrier separation on the charge-transfer mechanism in the PSCs is elucidated by using the results of ferroelectric and structural studies on the perovskite. The ferroelectric polarization contributes to an inherent carrierseparation effect and the I–V hysteresis. The ferroelectric and semiconducting synergistic chargeseparation effect gives an alternative category of solar cells, ferroelectric semiconductor solar cells. Our findings identify the ferroelectric semiconducting behavior of the perovskite absorber as being significant to the improvement of the ferroelectric PSCs performances in future developments.
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    Controlling dye coverage instead of addition of organic acid to reduce dye aggregation in dye-sensitized solar cells
    (Elsevier, 2020) Sewvandi, GA; Kakimoto, M; Chen, C; Hu, D; Abeygunawardhana, PKW; Feng, Q
    The photo-generated electron injection yield of dye-sensitized solar cells (DSSCs) based on donor-acceptor conjugated dyes is lowered by the aggregation of surface adsorbed organic dyes that pose a low-photoenergy conversion efficiency. Coadsorbates used to prevent the aggregation cause to decompose or detach the dye molecules anchored on the TiO2 surface. In this study, the effect of coadsorption of organic acid and organic dyes on photovoltaic performances was systematically scrutinized by means of adsorption isotherms and photovoltaic measurements. Our laboratory synthesized {0 1 0}-faceted TiO2 (PA TiO2) and P25 TiO2 were used as mesoporous nanocrystals, D149 organic dye was used as a sensitizer and cheno-deoxycholic acid, CDA, was used as a coadsorbate. The coadsorption of CDA reduces the adsorption parameters, maximum adsorption density (Qm) and adsorption constant (Kad), and the reduction depended on the type of TiO2. The photovoltaic performance indicates that the D149 dye has the best dye coverage at around 70% for the effective photovoltaic energy conversion. The coadsorption of CDA increased the photovoltaic performances of DSSCs based on P25 TiO2 but, CDA decreased the photovoltaic performances of DSSCs based on PA TiO2 due to the reduction of the dye coverage below 70%. The results suggest that the coadsorption of organic acids is not necessary if the particular TiO2 can maintain its coverage at the best coverage. Thus, the requirement of coadsorbates to reduce the dye aggregation depends on the type of TiO2 used in DSSCs.