High efficiency inverted polymeric bulk-heterojunction solar cells with hydrophilic conjugated polymers as cathode interlayer on ITO

• Published in: Solar energy materials and solar cells Vol. 97; pp. 83 - 88
• Main Authors: Zhu, Yongxiang, Xu, Xiaofeng, Zhang, Lianjie, Chen, Junwu, Cao, Yong
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 01.02.2012; Elsevier
• Subjects: Applied sciences; Cathode interlayer polymer; Cathodes; Devices; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Energy; Exact sciences and technology; Hydrophilic conjugated polymer; Indium tin oxide; Interface modification; Interlayers; Inverted solar cell; Low band gap polycarbazole; Natural energy; Photoelectric conversion; Photovoltaic cells; Photovoltaic conversion; Polyvinyl chlorides; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Volatile organic compounds; Inverted solar cell; Interface modification; Low band gap polycarbazole; Cathode interlayer polymer; Hydrophilic conjugated polymer; Interfacial layer; Performance evaluation; Interlayers; Conversion rate; Surfactant; Fill factor; Butyric acid; Low voltage; Ester; Conjugated polymer; Work function; Tin addition; Energy conversion; Copolymer; Heterojunction; Cathode; Indium oxide; Open circuit voltage; Solar cell; Carbazole polymer; High efficiency
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2011.09.030

In this work, alcohol-soluble 2,7-carbazole-1,4-phenylene copolymers PCP-NOH and PCP-EP, comprising surfactant-like diethanolamino and phosphonate end groups on the side chains, respectively, were utilized as cathode interlayer on ITO to construct inverted solar cells based on a low band gap poly(2,7-carbazole) (PCDTBT) as the polymer donor and [6,6]-phenyl C 71-butyric acid methyl ester (PC 71BM) as the acceptor. The work functions of ITO were shifted to −4.2 and −4.3 eV by PCP-NOH and PCP-EP, respectively, which can well match the LUMO level of PC 71BM for good electron extraction. The power conversion efficiency (PCE) of the inverted solar cells without the cathode interlayer was only 1.63%, because of very low open-circuit voltage ( V oc, 0.48 V) and fill factor (FF, 36.9%). Using PCP-NOH and PCP-EP as cathode interlayers significantly improved V oc to 0.88 V and FF to ∼58%, giving PCEs of 5.39% and 5.48%, respectively. The increasing extents of PCEs by the interlayers are over 230%. The PCEs achieved by PCP-NOH and PCP-EP belong to the top device performances so far reported for the inverted PVCs with an organic cathode interlayer. Our results suggest that hydrophilic conjugated polymers are promising candidates as a cathode interlayer in high efficiency inverted solar cells through the modification of interface contacts. [Display omitted] ► Hydrophilic conjugated polymer as cathode interlayer on ITO. ► Interlayer polymer shifts ITO work function to ∼4.3 eV. ► High efficiency inverted solar cells. ► PCE increasing 230% when compared with bare ITO.