摻雜碳酸鹽之水溶性富勒烯衍生物於有機光伏電池的應用

Abstract

本研究設計二個合成簡易的水溶性碳六十衍生物作為電子傳輸層，分別為BTGMF-OH 及 BTGMF-COOH。用環丙烷與碳六十相接做為橋樑，並導入親水性 ethylene glycol 基團，在親水性基團 ethylene glycol 末端導入二不同官能基-醇基與羧酸基的目的在於藉由這二個親水基團，使碳六十衍生物對極性溶劑的溶解度更強，可運用在濕式製程的多層結構有機太陽能電池元件中，解決多層元件層與層之間溶劑選擇的問題。研究中發現以共溶劑 2-ethoxyethanol + H2O 得到的效率最高。在元件中導入此碳六十衍生物之電子傳輸層，可提升電子擷取能力並扮演電洞阻擋層，以ITO/PEDOT:PSS/P3TH:PC61BM/water soluble C60 derivatives/Ca/Al 為結構製作的太陽能電池的效率明顯比未導入此電子傳輸層高，將元件效率從 3.61 % (對照組元件-不含水溶性碳六十衍生物)提升到 3.8 %。為了進一步提升水溶性碳六十衍生物的電子傳輸能力，在材料中摻雜碳酸鹽類使該電子傳輸層成為n型摻雜電子傳輸層，元件特性如下： BTGMF-OH ( Voc = 0.60 V, Jsc = 9.71 mA/cm2, FF = 65 %, PCE = 3.80 % )；BTGMF-COOH ( Voc = 0.60 V, Jsc = 10.9 mA/cm2, FF = 66 %, PCE = 4.29 % ) 藉由摻雜鹽類提升電荷傳輸能力，使 Jsc 值從 9.02 mA/cm2 提升至 10.9 mA/cm2，元件效率 3.61 % (不含水溶性碳六十衍生物)提升至 4.29 % 。我們更進一步地將 BTGMF-COOH 運用在以 PCDCTBT-C8:PC71BM為主動層材料之元件(ITO/PEDOT:PSS /PCDCTBT-C8:PC71BM/ BTGMF-COOH/Ca /Al )，其PCE與標準元件(不含水溶性碳六十衍生物之電子傳輸層)相比，從原本的 3.63 % 大幅提升至 4.51 %，Jsc 更高達 11.1 mA/cm2。實驗發現水溶性碳六十衍生物 BTGMF-COOH 在以非傳統 P3HT：PC61BM 為主動層的結構中亦能有效提升元件效率。

The new water soluble fullerene derivatives ( BTGMF-OH and BTGMF-COOH ) functionalized with ethylene glycol groups were synthesized and used as electron transport layer in organic photovoltaics. In order to enhance the solubility of fullerene derivatives in polar solvent, two different hydrophilic groups diol and diacid have been introduced to the molecular. The alcohol soluble feature of BTGMF-OH and BTGMF-COOH prevents interfacial mixing and erosion between the active layer and electron transporting layer, which is one of the most challenging problems in fabricating multilayer polymer solar cells by solution process. We used these fullerene derivatives as electron transporting materials to fabricate the bulk heterjunction ( BHJ ) solar cell devices with the configuration of ITO/PEDOT:PSS/P3HT:PC61BM/water soluble C60 derivatives/Ca/Al achieve enhanced device characteristics. The PCE values have been improved from 3.61 % to 3.80 % after modification with the BTGMF-OH and BTGMF-COOH interlayer. The unique solubility of BTGMF-OH and BTGMF-COOH offer the possibility to enhance electron conductivity by doping them with water soluble alkali or alkaline earth metal salts. Three carbonate salts ( Li2CO3, K2CO3 and Cs2CO3 ) were chosen as dopants for BTGMF-OH and BTGMF-COOH to improve the electron transporting ability in solar cells. The PCE values have been improved from 3.61 % to 4.29 % after modification with doped BTGMF-OH and BTGMF-COOH interlayer. Furthermore, this promising approach can be applied to another solar cell device modified with the doped BTGMF-COOH interlayer, ITO/PEDOT:PSS/PCDCTBT-C8:PC71BM/BTGMF-COOH/Ca/Al, using PCDCTBT-C8 as the p-type low-band-gap conjugated polymer. The PCE values have been improved from 3.63 % to 4.51 %. This interlayer exerts multiple positive effects on both polymer/BTGMF-COOH and PCBM/BTGMF-COOH interface, including improved electron transporting ability, exciton dissociation efficiency and reduced charge recombination. Based on our study, incorporation of water soluble fullerene derivatives interlayer could become a standard procedure in the fabrication of highly efficient and stable multilayer solar cells.