聚(3-己烷基噻吩)/二氧化鈦介面改質於混成太陽能電池光伏行為探討

Effect of P3HT/TiO2 interface modification on the photovoltaic behavior of hybrid solar cells

沈宗龍(Tsung-Lung Shen)

指導教授 ： 王立義

國立臺灣大學/工學院/高分子科學與工程學研究所/碩士(2008年)

https://doi.org/10.6342/NTU.2008.00841

摘要

在本篇論文研究中，我們將P3HT與規則中孔性TiO2製成有序型混掺異質介面型太陽能電池，藉由提供較多異質介面接觸面積以提升更多電荷分離的機會，進而達到增加元件效率的目的。
首先，我們以(EO)20(PO)70(EO)20作為結構指示劑，與TiO2前趨液進行自組裝排列，再利用拉伸塗佈法製備中孔性TiO2薄膜；藉由FE-SEM及XRD的鑑定可以得知，經過450℃高溫燒結過後，其孔洞大小約為10 nm且皆為antase phase。隨後利用旋轉塗佈法將P3HT塗佈其上，並調控加熱時間與溫度控制P3HT滲入孔洞內的量，其結果可由UV-Vis發現會有明顯藍位移發生。
由於P3HT/TiO2之間極性差異極大，介面間存在著許多缺陷，不利於電荷分離及傳遞，造成這一系列元件短路電流都無法超過1 mA/cm2 (A.M. 1.5G，100mW/cm2)，為了進一步改善P3HT/TiO2之間極性的差異，我們嘗試以GRIM合成法，合成支鏈末端帶羥基的P3HT (P3HT-OH)，由1H-NMR鑑定羥基所佔比例約為10 %，並且經由gel permeation chromatography (GPC)鑑定分子量約為25000；藉由羥基與二氧化鈦表面羥基有較好的親合性，期待能改善元件異質介面間的缺陷；然而由UV-Vis吸收光譜可以發現，P3HT-OH的結晶性及共軛長度皆低於P3HT，使得元件串聯電組上升，導致短路電流不如原先預期。
為了進一步解決介面間的問題，我們實驗室自行設計合成一系列低能階介面改質劑(WL-1 ~ WL-4)，一方面修飾TiO2表面極性，另一方面調整共軛長度使其能階介於TiO2與P3HT之間，幫助電荷分離及傳導；藉由在中孔性TiO2表面形成自組裝單層膜(SAMs)，將這一系列介面改質劑導入P3HT/TiO2之間，其元件短路電流在A.M. 1.5G (100 mW/cm2)太陽光模擬光源量測下皆突破至1 mA/cm2以上；其中以WL-4改質過後的元件效果最為顯著，VOC為800 mV、JSC為2.3 mA/cm2、FF為55 %且η為1.01 %，而EQE更從未改質前2.5 %大幅增漲至11 %。

關鍵字

有機太陽能電池 ； 聚(3-己烷基噻吩) ； 中孔性二氧化鈦 ； 介面改質劑 ； 自組裝單層膜

並列摘要

In this article, we fabricated the ordered BHJ solar cells based on P3HT and ordered mesoporous TiO2 film which affords more hrterojunction area for charge separation and direct path for charge transport.
Firstly, mesoporous TiO2 films were prepared by dip-coating a EtOH solution of titania precursor and structure-directing triblock copolymer, (EO)20(PO)70(EO)20, on a densed TiO2-covered/SnO2:F (FTO) glass substrate, followed by sintering at 450℃. Experimental results of FE-SEM and XRD indicated the thus prepared TiO2 had order mesoporous structure with a pore diameter of around 10 nm and was in all anatase phase. Subsequently, the ordered BHJ solar cells was prepared by spin-coating P3HT on top of the mesoporous TiO2 film and then at different temperature for various periods. Experimental results of UV-Vis data showed a visible blue-shift after heat treatment, reveling the intriltration of P3HT into the mesooprpus TiO2 resulted in the formation of a more coil-like structure.
In order to improve the compatibility of P3HT and TiO2, a OH-bearing polythiophene, poly[3-(6-hydroxyl- hexanyl)thiophene-co-3-hexylthiophene) (P3HT-OH), was synthesized via the GRIM method using 2-bromo-3-hexylthiophene and 2-bromo-3-(6-(2-tetrahydropyranyloxy)hexyl)thiophene as monomers, followed by the deprotection of OH moieties with HCl. 1H-NMR and gel permeation chromatography (GPC) data revealed the copolymer contained 10 % of hydroxyl group and had a weight-average molecular weight (Mw) of about 25000. Subsequently, the device was fabricated by replacing P3HT with P3HT-OH. However, the JSC of the device is lower than that of the reference device. The UV-Vis spectrum of P3HT-OH/TiO2 film showes the P3HT-OH has shorter conjugation length and less crystallinity than P3HT, which may correspond to the increase in series resistance (RS) and then the decrease in JSC.
Morever, a series of low bandgap thiophene-based molecules (WL-1~WL-4) that possess a LUMO level beyween the LUMO of P3HT and the conduction band of TiO2 as surface modifier of TiO2. After modifying TiO2 film with WL-1 ~ WL-4 by self-assembled monolayers mothod (SAMs), all JSC were higher than 1 mA/cm2 ( under A.M. 1.5G, 100 mW/cm2). The cell with WL-4 as interface modifier gave the best photovoltaic properties with a VOC of 0.8 V, a JSC of 2.3 mA/cm2, and power conversion efficiency of 1.01 % (under A.M. 1.5G, 100 mA/cm2), and external quantum efficiency (EQE) was substantially increased from 2.5 % (for the reference device) to 11 %.

並列關鍵字

organic solar cells ； poly(3-hexylthiophene) ； mesoporous TiO2 ； interface modifier ； self-assembled monolayers

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