Here comes the sun: A conversion efficiency as high as 5.4 % has been achieved on dye‐sensitized ZnO solar cells with photoelectrode films consisting of polydisperse aggregates, compared to 2.4 % for the films with only nanosized crystallites. The aggregation of nanocrystallites with a broad size distribution is effective in enhancing the light‐harvesting efficiency by inducing light scattering within the photoelectrode films.
ZnO films consisting of either polydisperse or monodisperse aggregates of nanocrystallites were fabricated and studied as dye‐sensitized solar‐cell electrodes. The results revealed that the overall energy‐conversion efficiency of the cells could be significantly affected by either the average size or the size distribution of the ZnO aggregates. The highest overall energy‐conversion efficiency of ∼4.4% was achieved with the film formed by polydisperse ZnO aggregates with a broad size distribution from 120 to 360 nm in diameter. Light scattering by the submicrometer‐sized ZnO aggregates was employed to explain the improved solar‐cell performance through extending the distance travelled by light so as to increase the light‐harvesting efficiency of photoelectrode film. The broad distribution of aggregate size provides the ZnO films with both better packing and an enhanced ability to scatter the incident light, and thus promotes the solar‐cell performance.
In this paper, we report the solar cell performance of titania (TiO 2 ) film electrodes with various particle sizes. It was found that the TiO 2 nanoparticle film with smaller particles ∼10 nm in diameter resulted in a lower overall light conversion efficiency of ∼1.4% with an open-circuit voltage of ∼730 mV, a short-circuit current density of ∼3.6 mA/cm 2 , and a fill factor of ∼54%. Larger particles ∼23 nm in diameter resulted in a higher efficiency ∼5.2% with an open-circuit voltage of ∼730 mV, a short-circuit current density of ∼12.2 mA/ cm 2 , and a fill factor of ∼58%. Although it was anticipated that particles with smaller diameters would adsorb more dye because of their larger surface area, it was found that particles with larger diameters had better dye adsorption for increased electron-hole generation, resulting in higher short-circuit current density and overall light conversion efficiency. Larger particles were shown to have better dye adsorption, indicating that films consisting of larger particles had greater effective surface area for greater photon absorption and electron-hole generation.
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