Anchor 分子吸附於NiO(100)之表面: 利用理論計算方法之研究

Abstract

我們利用週期性密度泛函理論，研究P-type染敏化太陽能染料電池半導體表面和染料anchor分子之間作用的關係。我們主要選擇了四種常見的anchor分子，分別是Carboxylate分子、Phosphonate分子、Carbodithioate分子以及Hydroxamate分子，作用在常見P-type半導體的NiO表面上。藉著週期性的運算，了解anchor分子在表面吸附的穩定性，尋找穩定的吸附結構。找到穩定的吸附結構之後，透過吸附前後電荷的差異，以判斷哪一種anchor分子可以有效的作為電荷傳遞的橋樑。接著我們使用投影態密度了解哪一類型的軌域是anchor分子和表面原子的主要鍵結。之後利用態密度分析，以判斷表面電子注入至anchor分子所需要的時間。利用以上詳細的方法，分析哪一種anchor分子和NiO有較好的作用。最後我們發現Phosphonate分子有較好的效果在NiO的表面上。計算出來的吸附能為-1.562 eV 雖然沒有Carbodithioate分子吸附能-2.527 eV表現來的好，但是在電荷轉移到NiO的部分，Phosphonate分子是損失最少的，並且在最穩定的吸附結構構型時，phosphonate分子的態密度重疊的比率最高，有達到22%，電子從NiO表面注入到anchor分子所需要的時間也僅有4.93 fs，種種的表現都足以證明phosphonate是可以取代傳統運用在染料分子的Carboxylate分子，並且phosphonate分子是適用在p-type染敏化太陽能染料電池的電極表面上。We used Density Functional Theory (DFT) to study the p-type Dye-Sensitized Solar Cell (DSSC). The semiconductor materials of the electrode surface as well as the anchor group dye paly important for the process electronic injection. We have chosen four anchor molecules commonly seen in the experiment and that included carboxylate, phosphonate, carbodithioate, and hydroxamate molecules chemically bonded with NiO (100) surface. The molecular anchoring was approximately simulated using periodic bound condition where the absorbent stability and the stable molecular structure were affected by the neighboring cells. After the stable geometries were located, the charge effect was analyzed and compared before and after the anchor adsorption in order to understand the charge transfer effect as well as the molecular orbital coupling along. Then we calculated the projected density of state (PDOS) to estimate the anchor surface coupling effect by numerically integrating the overlapped DOS of surface and anchor. The numerical value of coupling was furthur adapted in an empirical formula reported in the literature to estimate the time scale of electron injection. Finally, we predicted phosphonate molecule possessing the best performance with NiO surface. The adsorption energy of phosphonate was calculated to be -1.562 eV , and despite the strongest binding energy was found to be using carbodithioate at -2.527 eV the chargre transfer behavior from phosphonate to NiO surface has least loss. The coupling of phosphonate reached to 22% and the corresponding electron injected from the surface ofthe anchor molecule was predicted to be only 4.93 fs. Thus, the adaption of phosphonate anchor to p-type DSSC is recomanded.