A new alcohol-soluble electron-transporting molecule for efficient inverted polymer solar cells

• Published in: Organic electronics Vol. 14; no. 9; pp. 2164 - 2171
• Main Authors: Li, Jing, Huang, Xiaodong, Yuan, Jianyu, Lu, Kunyuan, Yue, Wei, Ma, Wanli
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2013; Elsevier
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Electron transporting layer; Energy; Exact sciences and technology; Fullerenes and related materials; diamonds, graphite; Inverted polymer solar cells; Materials science; Methods of nanofabrication; Natural energy; Photovoltaic conversion; Physics; Self-assembled monolayer; Self-assembly; Small molecules; Solar cells. Photoelectrochemical cells; Solar energy; Solution-processed; Specific materials; Small molecules; Self-assembled monolayer; Inverted polymer solar cells; Electron transporting layer; Solution-processed; Self-assembled layer; MO method; Molecular orbital; Fullerene compounds; Electron transport layer; Conversion rate; Organic solar cells; Butyric acid; Ester; Tin addition; Thiophene derivative polymer; Energy conversion; n type semiconductor; Dicarboxylic acid; Zinc oxide; Small molecule; Growth from solution; Bathocuproine; II-VI compound; New product; Cathode; Active layer; Doped materials; Buffer system; Indium oxide; Manufacturing process; Phenanthrolines; Large scale
• ISSN: 1566-1199; 1878-5530
• DOI: 10.1016/j.orgel.2013.05.012

A new electron-transporting material 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPA) was synthesized by modifying a n-type small molecule bathocuproine (BCP). DPPA inherits the excellent electron collecting and transporting property from BCP. In addition, DPPA demonstrated more stable and efficient performance than BCP under various processing conditions, likely due to the improved film quality and better hole-blocking. More importantly, this work brings up a fast and economical approach to obtain efficient, solution-processible buffer layer materials by modifying the existing functional molecules with corresponding electron-withdrawing/donating groups. [Display omitted] •A new electron-transporting material DPPA was synthesized by modifying BCP.•DPPA outperforms BCP and ZnO as electron transporting layer in polymer solar cells.•The HOMO of DPPA is deeper than BCP, making it a better hole-blocking material.•DPPA shows a higher tolerance and flexibility for processing conditions than BCP.•A fast and economical approach was demonstrated to obtain buffer layer materials. A new electron-transporting material 4,7-diphenyl-1,10-phenanthroline-2,9-dicarboxylic acid (DPPA) was synthesized by modifying a n-type small molecule bathocuproine (BCP). The introduced carboxyl groups make DPPA soluble in polar solvent and compatible with large-scale solution-processing techniques. The anchoring of carboxyl on ZnO (or ITO) substrates helps to form a DPPA electron transporting layer, building an improved interfacial contact between the substrate and active layer. Furthermore, the highest occupied molecular orbital level of DPPA shifts to −6.45eV, which is 0.38eV deeper than that of BCP, suggesting enhanced hole-blocking. Inverted polymer solar cells using P3HT:PCBM blend as the active layer and DPPA modified ZnO as the electron transporting layer were fabricated. A power conversion efficiency (PCE) of 3.55% was obtained, which is about 10% higher than that of the conventional ZnO buffered devices (3.25%). The DPPA was also used to replace ZnO as the sole electron-extracting layer, resulting in an improved PCE of 3.46%, which indicates that DPPA-ETL/ITO forms a better cathode than conventional ZnO/ITO.