利用添加奈米點改質電洞傳導層聚二氧乙基塞吩-聚(磺酸苯乙烯)以增加有機太陽能電池元件效率

Abstract

聚二氧乙基塞吩 : 聚(磺酸苯乙烯) (PEDOT:PSS)由於具有良好的光穿透度以及導電性，因此常被拿來作為有機光電元件中的載子傳導材料。本篇將不同混摻物添加進入電洞傳導層PEDOT:PSS後，利用原子力探針顯微鏡探討其表面型態的變化以及PEDOT:PSS之間相分離的情況，並且使用空間電荷限制電流法 (space charge limited current method) 以及四點探針法 (four point probe method) 觀察加入不同添加物進入電洞傳導層後其電性變化，由於我們所使用的添加物-奈米點溶液是由溶劑四氫呋喃以及聚矽酸奈米粒子所組成。利用空間限制電流法，我們發現添加物的電洞阻擋的現象主要來自於溶劑四氫呋喃，而添加聚矽酸奈米粒子進入PEDOT:PSS後,其奈米粒子的表面電位可以有效屏蔽聚二氧乙基塞吩以及聚磺酸苯乙烯兩者之間的電荷，並且幫助電洞的傳導。除此之外我們也利用表面改質的方法，利用APTES置換奈米點上表面原本具有的氫氧根基團(PND-OH)而得到表面接附上較長鏈段基團且末端為胺根官能基的的奈米點(PND-NH2)。我們將不同的聚矽酸奈米粒子溶液添加到PEDOT:PSS中塗佈成膜後，應用到兩種有機太陽能電池P3HT/TiO2 以及P3HT/PCBM系統中。我們將表面接附不同官能基的奈米點添加到PEDOT:PSS電洞傳導層並且應用到P3HT/TiO2太陽能電池中，並且發現添加兩種奈米點都能夠有效提升P3HT/TiO2太陽能電池的元件效率，但是表面具有胺根基團的奈米點(PND-NH2)效率提升幅度較大，這可能是來自於此奈米點所具有的較高表面電位，如此一來加入表面具有胺根基團的奈米點(PND-NH2)可以更有效的屏蔽聚二氧乙基塞吩以及聚磺酸苯乙烯兩者之間的電荷。然而將兩種奈米點添加到P3HT/PCBM系統的電洞傳導層中，所得到的結果卻截然不同。這樣的結果顯示在電子以及電洞兩者遷移率較為平衡的P3HT/PCBM系統中，加入帶有正表面電位的奈米點以及負表面電位的奈米點，其電洞阻擋效果與電荷屏蔽效應兩者之間互相競爭，進而導致添加不同比例的奈米點後P3HT/PCBM元件出現效率增加或是降低兩種截然不同的情形。

Due to the good transparency and conductivity of Poly(3,4ethylenedioxythiophene) -polystyrenesulfonic acid (PEDOT:PSS), it commonly used as carrier transport material in organic photovoltaic devices. In this work, morphology change and phase separation of different doped PEDOT:PSS film are studied by AFM to explore the influence of different additive in PEDOT:PSS hole transport layer. Otherwise, we also used different methods like space charge limited current and four point probe method to detect electric properties of corresponding doped PEDOT:PSS films. The additive, Polymeric nanodot (PND) solution is composed of solvent tetrahydrofuran (THF) and polysilic acid. The space limited charge current fitting curves revealed that hole-blocking effect was attributed from the solvent THF instead of polysilic acid, however the polysilic acid doped in PEDOT:PSS polymer complex could help the hole transport by inducing charge screening between PEDOT:PSS. We also applied these doped PEDOT:PSS layer into two different polymer solar cell : P3HT/TiO2 and P3HT/PCBM hybrid solar cell, the doping of PND-OH and PND-NH2 can enhance the power conversion efficiency of P3HT/TiO2, but in P3HT/PCBM solar cell system, PND-NH2 and PND-OH doped samples exhibited different characteristic. The reason for efficiency enhancement and reduction of different PND doping ratio in PEDOT:PSS layer was interesting, we thought the balance of electron and hole mobility in P3HT/PCBM system is better than P3HT/TiO2 system. The addition of particles of negative or positive surface potential would induce hole-blocking effect and charge screening effect between PEDOT and PSS. As the result, the performance of doped sample would change by the competition of above two effects decided by different ligand capped on PND and corresponding doping ratio in PEDOT:PSS.