以四氯駢苯二醯亞胺作為架橋之超分枝聚噻吩衍生物之合成及光電性質研究

Abstract

本研究之目的在合成出以四氯駢苯二醯亞胺作為架橋之超分枝聚噻吩衍生物，並探討其光學、電性及電化學性質。這些材料可作為主動層材料以製作高分子太陽能元件。本研究同時製備以柔軟碳鏈為架橋之超分枝高分子以作為對照之用。 利用Universal GRIM途徑合成之架橋高分子其立體規則度皆達97%以上。所有高分子之數量平均分子量經測定為1.69–3.41×104 g/mol，重量平均分子量則為3.16–6.31×104 g/mol，PDI皆在2以下。引入雙頭架橋單體之聚噻吩分子量皆較P3HT為大。所有高分子呈現第一階段熱損失溫度在300 oC左右，擁有剛硬四氯駢苯二醯亞胺團基之高分子P1經高溫加熱後，相較於P3HT熱重損失量較小，確實增強材料的熱穩定性。 所有超分枝高分子薄膜態的最大吸收峰皆與P3HT大致相符，且肩峰強度皆較P3HT強，顯示引入架橋結構拉近主鏈之間的距離。所有高分子之螢光放射波長差異不大，同時衰減的放射強度顯示這些材料中激子不易經由再結合而放光，若運用於有機元件中載子有更多機會傳遞至兩端電極。電化學分析顯示引入架橋結構致使LUMO能階下降，且HOMO能階也下降。 將所有高分子應用於元件結構ITO/PEDOT/polymer:PCBM (1:1 w/w)/LiF/Al之有機太陽能電池並測量其性質。P3HT:PCBM元件之光電轉換效率值為0.96%，超分枝高分子元件效率則介於0.65–0.90%之間。本研究最後以AFM掃描P3HT、P2、P3與PCBM摻混薄膜，確認P3HT:PCBM及P3:PCBM薄膜的塊狀分布均勻，P2:PCBM薄膜則為局部塊狀聚集且分布不均。上述結果可用以闡明元件之效率趨勢。

The goal of this research is to synthesize the hyperbranched polythiophene derivatives containing tetrachloroperylene bisimide as bridging moiety, and to investigate the optical, electrical, and electrochemical properties of those derivatives. Those materials can be used as active layer for fabrication of organic solar cells. The polymers containing soft alkyl spacer as bridging moiety were also synthesized for comparison in this study. Polymers with high regioregularity > 97% were synthesized via the Universal Grignard metathesis. The number-average molecular weights of polymers are in the range of 1.69–3.41×104 g/mol, while their weight-average molecular weights are in the range of 3.16–6.31×104 g/mol, with PDI values less than 2. The molecular weights of hyperbranched polythiophenes are higher than that of P3HT. All polymers show a first-stage weight loss at about 300 oC; polymer P1 containing rigid perylene bisimide groups possess less weight loss than P3HT after heating, indicative of enhanced thermal stabilities. The maximum UV-vis absorptions of all hyperbranched polymers are similar to that of P3HT in film state, while absorption intensities of their shoulder bands are stronger than that of P3HT, indicating shorter distance between backbones after introduction of bridge architecture. All polymers show insignificant difference in PL emission wavelength. Meanwhile, attenuation of fluorescent intensity of hyperbranched polymers demonstrates that excitons are not easy to recombine to emit light in those materials, implying more opportunity for carriers to transport to both electrodes. Electrochemical analysis shows that introducing hyperbranched structure results in decreasing LUMO levels, and HOMO levels are lowered as well. All polymers were used for fabrication of organic solar cells with the configuration of ITO/PEDOT/polymer:PCBM(1:1 w/w)/LiF/Al to evaluate their performance. The power conversion efficiency (PCE) of the P3HT:PCBM-based device is 0.96%, while devices based on hyperbranched polymers showed PCE values in the range of 0.65–0.90%. Finally, thin films of P3HT, P2, or P3 blending with PCBM were scanned by AFM in this research. P3HT:PCBM and P3:PCBM thin films were recognized to show homogeneous bulk distribution, while uneven distribution of bulks was observed for P2:PCBM thin film. The above results can be used for interpretation of efficiency trend of devices.