The inverted device architecture of polymer solar cell (i-PSCs) is an attractive approach for its superior long-term stability compared to the initially implemented conventional device structures. To facilitate charge extraction, electron-collecting (EC) interlayer is highly demanded since commonly utilized Indium Tin Oxide (ITO) is not regarded as good EC electrode due to its high work function. Both conjugated and non-conjugated polyelectrolytes (CPE and NCPE) have been demonstrated as promising EC-interlayer materials for i-PSCs. Starburst molecules are well-known featured as well-defined chemical structure, high purity, excellent reproducibility, good solution processibility, and generally resulting superior optoelectronic properties. Such promising characteristics of monodisperse macromolecules make it rather attractive for organic optoelectronic applications.[1,2] We have successfully fabricated i-PSCs using TrNBr and TrOH, two monodisperse star-shaped conjugated macro-electrolytes as EC interlayers on the top of ITO electrode substrates.[3] The device structure is ITO/EC-interlayer/P3HT:ICBA/V2O5/Ag. The thickness of each interlayer was tuned carefully, exhibiting an optimized PCE for a thickness of ~2.4 nm in the case of TrNBr and of ~8.7 nm in the case of TrOH. Following optimization the solar cells devices delivered a maximum PCE of 4.88% (when TrNBr was used) and of 4.74% (when TrOH was used) with the benefit of avoiding the requirement for reactive metals to be used as EC-electrodes; that is an improvement of more than 20% in respect to the conventional Ca/Al reference devices. In comparison to the sol-gel derived ZnO based inverted devices, the enhancement in PCE was of 16% and 13%. The utilization of the star-shaped conjugated macro-electrolytes as interlayers in iPSCs resulted in the increase of the device stability when compared with devices of conventional geometry. Advantageously, the solution-processable character of these interlayer materials and their easy processing at low-temperatures in ambient atmosphere, offer a great promise for their incorporation in PSC device fabrication for commercial applications.
[1] W. Xu, W.-Y. Lai, Q. Hu, X. Y. Teng, X. W. Zhang, W. Huang, Polym. Chem. 2014, 5, 2942. [2] W. Xu, X. Zhang, Q. Hu, L. Zhao, X. Teng, W.-Y. Lai, R. Xia, J. Nelson, W. Huang, D. D. C. Bradley, Org. Electron. 2014, 15, 1244. [3] W. Xu, Z. Kan, T. L. Ye, L. Zhao, W.-Y. Lai, R. Xia, G. Lanzani, P. E. Keivanidis, W. Huang, ACS Appl. Mater. Interfaces 2015, 7, 452.