Abstract
In this work, microwave synthesis, chemical, optical and electrochemical characterization of three small organic molecules, TPA-TPD, TPA-PT-TPD and TPA-TT-TPD with donor-acceptor structure and their use in organic photovoltaic cells are reported. For the synthesis, 5-(2-ethylhexyl)-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione was used as electron withdrawing fragment while the triphenylamine was used as electron donating fragment. Molecular electronic geometry and electronic distribution density were established by density functional theory (DFT) calculations and confirmed by optical and chemical characterization. These molecules were employed as electron-donors in the active layer for manufacturing bulk heterojunction organic solar cells, where [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) was used as electron-acceptor. As cathode, Field′s metal (FM), an eutectic alloy (Bi/In/Sn: 32.5%, 51%, and 16.5%, respectively) with a melting point above 62 °C, was easily deposited by drop casting under vacuum-free process and at air atmosphere. Prepared devices based on TPA-TPD:PC71BM (1:4 w/w ratio) presented a large VOC = 0.97 V, with JSC = 7.9 mA/cm2, a FF = 0.34, then, a power conversion efficiency (PCE) of 2.6%.
Highlights
The synthesis and study of organic semiconducting molecules have increased considerably in recent years due to their electronic and optoelectronic properties [1,2,3,4,5]; it is because their chemical structure can be modified, resulting in a large number of organic molecules with tunable electronic and optoelectronic characteristics
Molecules 2017, 22, 1607 molecules are being used in the manufacture of organic solar cells (OSCs) [6,7,8,9], organic thin film transistors (OFETs) [10,11,12] and organic light emitting diodes (OLEDs) [13,14,15]
TPA-TPD, TPA-PT-TPD and TPA-TT-TPD molecules were synthesized by using microwave assistance and decreasing the reaction time from 48 to 1 h
Summary
The synthesis and study of organic semiconducting molecules have increased considerably in recent years due to their electronic and optoelectronic properties [1,2,3,4,5]; it is because their chemical structure can be modified, resulting in a large number of organic molecules with tunable electronic and optoelectronic characteristics Due to these optical and electrical properties, organic. The synthesis strategy of SMs for OSCs applications has focused mainly on molecules where an electron donating fragment (donor D) is covalently bounded to an electron withdrawing fragment (acceptor A) obtaining a Donor-Acceptor structure This structure helps to modulate the energy difference between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) in order to obtain high open circuit voltage (VOC ) values in photovoltaic devices [24,25,26,27]. The use of TPD in the synthesis of SMs has been limited to some molecules in comparison with derivatives from
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