三苯胺硫二苯胺系列雙錨基有機染料應用於染料敏化太陽能電池

Abstract

合成三苯胺硫二苯胺染料（TY1-TY3）作為無金屬的有機染料，應用於染料敏化太陽能電池（DSSC）。引入三苯胺(TPA)作為硫二苯胺(PTZ)的N-取代基，目的在於作為二級電子予體並建立階層式電荷轉移通道，增加主要電子予體PTZ的電荷轉移(ICT)至錨基，且提供快速的染料再生。以4-(hexyloxy)phenyl (-OC6H13)或4-(hexylthio)phenyl (-SC6H13)取代基的三苯胺硫二苯胺核心，與3-hexylthiophene連接，得到TY1。同樣的，當使用 4,4-bihexyl-4H- cyclopenta[2,1-b:3,4-b']dithiophene (CPDT)作為共軛架橋，則會得到TY2和TY3。當TPA主體上的取代基從4-(hexyloxy)phenyl轉換成 4-(hexylthio)phenyl (TY2到TY3)時，發現染料的ICT吸收峰藍移且HOMO/LUMO能階顯著的提高，是由於烷硫取代基的推電子特性比含氧類似物更強。因此基於TY3的染敏電池元件表現出低於3%的效率，歸因於 4-(hexylthio)phenyl取代基的存在，導致無效率的電子注入。當共軛架橋從3-hexylthiophene延伸到CPDT（TY1到TY2）時，ICT吸收帶變窄、莫耳消光係數變高，但HOMO/LUMO能階維持不變。這種現象指出共軛長度的延伸不利於TY染料的光吸收，從而不利於電子注入。在所有TY染料中，當TY1含有鵝去氧膽酸(CDCA)作為共吸附劑，在一個太陽光的條件下，表現出良好的光電轉換效率達 10.47%；此裝置效率優於N719 (9.50%)和HL5 (8.53%)。這些結果歸因於TY1具有適當的光吸收範圍、有效的電子注入、良好的階層式電荷轉移通道和快速的染料再生。在室內照明（Philips T5 lamp）下，基於TY1的染敏電池在1000 lux、600 lux 和300 lux下分別達到了21.2%、19.5% 和16.8%的光電效率，顯示出染敏電池在物聯網 (IoT)應用上的無限潛力。

Triphenylamine-tethered phenothiazine-based dyes (TY1–TY3) were synthesized and used as the metal-free organic sensitizers for dye-sensitized solar cells (DSSCs). Triphenylamine (TPA) entity was introduced as the N-substituent of phenothiazine (PTZ) to function as a secondary donor for building up a cascade charge transfer channel, which may enhance the intramolecular charge transfer (ICT) from PTZ to the anchors and provide fast dye regeneration. The 4-(hexyloxy)phenyl-substituted (–OC6H13) or 4-(hexylthio)phenyl-substituted (–SC6H13) TPA-tethered PTZ core were connected with 3-hexylthion π-bridge to afford TY1. Similarly, the 4-(hexyloxy)phenyl-substituted or 4-(hexylthio)phenyl- substituted TPA-tethered PTZ core were connected with the π-brigde of 4,4-bihexyl-4H- cyclopenta[2,1-b:3,4-b']dithiophene (CPDT) to afford TY2 and TY3, respectively. When the substituents on the TPA entity was switched from 4-(hexyloxy)phenyl to 4-(hexylthio)phenyl (TY2 to TY3), there were obvious blue shift in the ICT absorption peak and dramatical elevation in the HOMO/LUMO level of the dyes. These can be attributed to the stronger electron-donating power of the alkylthio substituents compared with their oxygenated analogue. Thus, TY3-based DSSCs exhibited poor cell efficiencies (<3%) due to the ineffective electron injection from the dye to TiO2. When the π-brigde of 4-(hexyloxy)phenyl-substituted TPA-tethered PTZ core was changed from 3-hexylthiophene to CPDT (TY1 to TY2), the dye exhibited a narrower ICT absortion band with extinction coefficient, but retaining similar HOMO/LUMO levels. This indicated that the extension in the conjugation length of 4-(hexyloxy)phenyl-substituted dye was detrimental to light absorption and thereby electron injection. Among all the TY dyes, the optimal TY1-based DSSC with denodexylcholic acid (CDCA) co-adsorbent exhibits good solar-to-electricity conversion efficiency up to 10.47% at sun. This cell effiency which outperformed the N719-based (9.50%) and HL5-based DSSCs (8.53%). The results were attributed to the moderate light absorption range, effective electron injection, good cascade charge transfer channel, and fast dye regeneration of TY1. Under room light illumination (Philips T5 lamp), the TY1-based DSSC reached decent cell efficiencies: 21.2%, 19.5%, and 16.8% at 1000 lux, 600 lux, and 300 lux, respectively. Therefore, the new dyes have great potential to join in the Internet of Things (IoTs) application.