| 摘要: | 本論文合成出一系列含PM-BDP (4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora-3a, 4a-diaza-s-indacene)或PM-BDP’ (2,6-diacetyl-4,4-difluoro-1,3,5,7,8-pentamethyl-4-bora- 3a,4a-diaza-s-indacene)結構之化合物。這些具對稱性之化合物乃是以PM-BDP 與PM-BDP’為電子受體，並在兩端以不同共軛長度的「共軛架橋」聯結可作為電子予體之二苯胺基(diphenylamine)來構成。PM-BDP 系列化合物在450−600 nm 波長處的消光係數為46,400−81,600 M-1cm-1，而隨著分子具有較佳的共面性時，化合物具有較紅位移的光吸收波長與較高的消光係數；而PM-BDP’由於在2號和6號位置增加三鍵架橋基取代的化合物有更加的共面性，因此有更佳的光收成，可達76,200−84,900 M-1cm-1。經由理論計算，可發現這些分子除了具有π−π* 兼電荷轉移吸收特徵，也有良好的消光係數。PM-BDP 基團與相鄰之thiophene 有較大之二面角 (47.1−55.0o)，而PM-BDP’與共軛架橋的二面角 (11.4−12.7o) 相對較小。以此類含PM-BDP 結構之分子作為p-type材料，摻以PCBM (phenyl-C61-butyric acid methyl ester)作為n-type 材料，製作出BHJ 形式之有機光伏打電池(Organic Photovoltaic Cells，OPV)。當化合物FBF’ 與PCBM 以1:4 的摻混比例，並於溫度100 ℃下退火10 分鐘製作元件時，可得最佳的元件效率（1.50%）。同時，由於PM-BDP 與PM-BDP’系列分子的HOMO 能階較低，大部分化合物之元件都具有高開環電壓（VOC = 0.80−1.06 V)。PM-BDP’系列化合物有較佳的共軛，物理量測與理論計算皆顯示其有較強與較為紅位移之吸收光譜，但BBB’與2,7-CBC’在有機溶劑中溶解度較差，導致製成之元件效率也不佳。我們藉由原子力顯微鏡（Atomic Force Microscopy，AFM）觀看FBF’ 元件之表面型態（morphology），發現當與PCBM混摻比例為 1:1 時，材料表面有嚴重的堆疊而導致元件之電流密度較低；反之，當FBF’與PCBM 混摻比例為 1:4 時，元件之表面粗糙度相對較低，因而擁有較高之電流密度與轉換效率。 A new series of liner organic compounds containing 4, 4-difluoro-1,3,5,7,8- pentamethyl-4-bora-3a,4a-diaza-s-indacene (PM-BDP) or 2,6-diacetyl-4,4-difluoro- 1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (PM-BDP’) unit have been synthesized. These symmetric compounds have a common structural D-S-A-S-D motif, where D (diphenylamine) is the electron donor, A (PM-BDP or PM-BDP’) is the electron acceptor, and S is the π-conjugated spacer of different length. PM-BDP series of compounds have high molar absorption coefficients (46,400−81,600 M-1cm-1) in the region 450−606 nm, and the absorption coefficient and wavelength increase as the planarity of the molecules increases. Among the compounds, the PM-BDP’-based molecules with 2,6-substituted acetylene group have superior light-harvesting behavior (76,200−84,900 M-1cm-1) because of their better coplanarity. Theoretical computation on these molecules confirms that the longer wavelength absorption of the molecules indeed is π−π* transition with charge-transfer character. Therefore, they have large extinction coefficients. Except for the angle between PM-BDP’ and the neighboring thiophene groups (47.1−55.0o), all dihedral angles between two neighboring aromatic rings are fairly small (11.4−12.7o).The photovoltaic devices of BHJ configuration using these PM-BDP’-containing compounds and PCBM (phenyl-C61-butyric acid methyl ester) as the donor and the acceptor, respectively, were also studied. The photovoltaic cell fabricated with the blend of FBF’ and PCBM in 1:4 ratio and annealled at 100 ℃ exhibits the highest power conversion efficiency (η) reaching 1.50%. Most of the devices fabricated with the PM-BDP or PM-BDP’ molecules exhibited high open-circuit voltage (VOC) in the range of 0.80−1.06 V, which can be attributed to the more stabilized HOMO levels of the PM-BDP and PM-BDP compounds. In spite of good light-harvesting behavior, the low solubility of BBB’ and 2,7-CBC’ in common organic solvents prevented formation of films with good quality, which led to low performance of the devices. This is further evidenced by the atomicforce microscopy (AFM) image a plethora of aggregation was found for the blend of FBF’ and PCBM in 1:1 ratio,which led to low current density (JSC). On the contrary, the AFM image of the blend film of FBF’ and PCBM in 1:4 ratio showed rather flattened active layer, which resulted in high current density and power conversion efficiency. |
