氧化亞銅晶體在導電性、光催化活性和光學特性上，已被證明具有晶面效應。然而，氧化亞銅晶體在光電化學特性上的晶面效應仍不清楚。在本篇研究中，我們合成了可調控尺寸的立方體、立方八面體、八面體和菱形十二面體的氧化亞銅進行光電化學分析。因為能隙的偏移和粒徑大小相關，粒徑大小的影響也需被納入考量。在正面照光下，立方體皆表現出遠比其他形狀還強的光電流響應，這代表在光電化學特性上，晶面效應的重要性要大於能隙位移的影響，且氧化亞銅的{100}面具有最佳的光電轉換效率。與此相對，立方八面體的表現居中，並未展現如文獻所提之晶面接面對光催化性質有增強的效果。菱形十二面體表現微弱，而八面體則是最弱。為了更詳細地解釋光電化學的活性表現，從電化學量測得以建構出氧化亞銅晶體的能帶圖、能帶彎曲和光伏電壓，發現和光電化學實驗的結果無清楚的相關性。為了檢視電荷傳遞的過程，採用了背面照光的光電化學量測。尺寸居中的立方體光電化學活性提升較其他尺寸的立方體多，展現出尺寸的效應。菱形十二面體表現出最大的活性提升，表示堆疊的{110}面其電洞傳遞通過氧化亞銅-氧化銦錫接面的受限程度最大。我們可以得出的結論是氧化亞銅晶體在光電化學特性上具有明顯的晶面效應和些微的尺寸效應，可由受限於氧化亞銅-氧化銦錫接面之間的電洞傳遞主導。

Cu2O crystals have been demonstrated to show facet-dependent electrical conductivity, photocatalytic activity and optical properties. However, the facet effects on photoelectrochemical (PEC) properties of Cu2O crystals are still unclear. Herein, we have synthesized Cu2O cubes with tunable sizes, cuboctahedra (CO), octahedra (Oct), and rhombic dodecahedra (RD) for PEC analysis. The influence of particle size is also considered because of the size-related band gap shifts. Under front-side illumination, cubes show much better photocurrent responses than other shapes do. This suggests facet effect is more significant than band gap shifts for PEC properties, and the Cu2O {100} faces have the best photon-to-current efficiency. In contrast, the performance of CO is moderate, showing no facet junction effect. RD are weak, and Oct are the weakest. To interpret the PEC performances in detail, band diagram, band bending, and photovoltage of Cu2O crystals have been obtained, but the results do not show clear correlation to the measured PEC activities. To investigate the charge pathway effect, the PEC measurements under back-side illumination were also performed. The M-cubes display more enhanced PEC performance than other sizes of cubes, exhibiting the size effect. RD display the strongest enhancement in performance, showing their stacked {110} faces presents the most limited hole transport across the Cu2O‒ITO interface. We can conclude that PEC properties of Cu2O crystals are strongly facet-dependent and moderately size-dependent, with the hole transport across the Cu2O‒ITO interface playing a significant role.

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