In Situ Formation of MoO3 in PEDOT:PSS Matrix: A Facile Way to Produce a Smooth and Less Hygroscopic Hole Transport Layer for Highly Stable Polymer Bulk Heterojunction Solar Cells

• Published in: Advanced energy materials 2013-03, Vol.3 (3), p.349-355
• Main Authors: Shao, Shuyan, Liu, Jian, Bergqvist, Jonas, Shi, Shengwei, Veit, Clemens, Würfel, Uli, Xie, Zhiyuan, Zhang, Fengling
• Format: Article
• Language: English
• Subjects: ambient stability; bulk heterojunction; hole transport layer; hygroscopicity; Photovoltaic cells; polymer solar cells; Solar energy; TECHNOLOGY; TEKNIKVETENSKAP
• ISSN: 1614-6832; 1614-6840; 1614-6840
• DOI: 10.1002/aenm.201200609

A solution‐processed neutral hole transport layer is developed by in situ formation of MoO3 in aqueous PEDOT:PSS dispersion (MoO3‐PEDOT:PSS). This MoO3‐PEDOT:PSS composite film takes advantage of both the highly conductive PEDOT:PSS and the ambient conditions stability of MoO3; consequently it possesses a smooth surface and considerably reduced hygroscopicity. The resulting bulk heterojunction polymer solar cells (BHJ PSC) based on poly[2,3‐bis‐(3‐octyloxyphenyl)quinoxaline‐5,8‐diyl‐alt‐thiophene‐2,5‐diyl] (TQ1):[6,6]‐phenyl‐C71‐butyric acid methyl ester (PC70BM) blends using MoO3‐PEDOT:PSS composite film as hole transport layer (HTL) show considerable improvement in power conversion efficiency (PCE), from 5.5% to 6.4%, compared with the reference pristine PEDOT:PSS‐based device. More importantly, the device with MoO3‐PEDOT:PSS HTL shows considerably improved stability, with the PCE remaining at 80% of its original value when stored in ambient air in the dark for 10 days. In comparison, the reference solar cell with PEDOT:PSS layer shows complete failure within 10 days. This MoO3‐PEDOT:PSS implies the potential for low‐cost roll‐to‐roll fabrication of high‐efficiency polymer solar cells with long‐term stability at ambient conditions. A solution‐processed MoO3‐PEDOT:PSS used as hole transport layer in polymer solar cells (PSCs) is reported. This MoO3‐PEDOT:PSS composite film has smooth surface morphology. TQ1:PC70BM‐based PSCs incorporating this composite hole‐transport layer demonstrate a high PCE of 6.4%. Of more importance is the greatly improved ambient stability that can be achieved by replacing strongly hygroscopic PEDOT:PSS with a less hygroscopic MoO3‐PEDOT:PSS layer. This MoO3‐PEDOT:PSS composite film implies the potential for low‐cost roll‐to‐roll fabrication of efficient polymer solar cells with long‐term stability at ambient conditions.