New concept to break the intrinsic properties of organic semiconductors for optical sensing applications

Abstract

The space charge limit (SCL) effect is a universal phenomenon in semiconductor devices involving light emitting diodes, solar cells, and photodetectors. Typically, the SCL will exist in the condition of (1) unbalanced hole and electron mobility; (2) thick active layer; (3) high light intensity or dense photocarriers (electrons and holes) generation; and (4) moderate reverse bias. Through the study of plasmonic organic solar cells, we will show metallic nanostructures go beyond their optical functions to control recombination, transport, and collection of photocarriers generated from active organic materials. Through spatially redistributing light absorption at the active layer, the proposed plasmonic-electrical concept is fundamentally different from the hot carrier effect where photocarriers are generated from metallic nanostructures. The new plasmonic-electrical effect not only lays a physical foundation but also upgrades electrical properties for semiconductor devices [1]. We will also design different device structures to investigate and demonstrated how plasmonic-electrical [2] and plasmonic-optical [3] effects can be used to enhance device performances such as improving the light absorption of solar cells, increasing emission efficiency of light emitting devices, reducing dark current and enhancing sensitivity of photodetector as well as intensifying the surface enhanced Raman scattering for biosensor applications. Besides the optical (plasmonic) resonances from metal nanostructure, we will also use metal nanostructures to demonstrate electrical resonance which can be used for bistable and memory devices [4]. Consequently, exploiting both plasmonic-optical and plasmonic-electrical effects via metallic nanostructures will open up a more flexible and integrated way to design high-performance optoelectronic nanodevices. [1] W.E.I. Sha, X. Li, W.C.H. Choy, Scientific Reports, vol. 4, p. 6236 (10pp), 2014. [2] F.X. Xie, W.C.H. Choy, W.E.I. Sha, D. Zhang, S. Zhang, X. Li, C.W. Leung, J. Hou, Energy Environ. Sci., vol. 6, pp.3372 – 3379, 2013; D. Zhang, W.C.H. Choy, F. Xie, W.E.I. Sha, X. Li, B. Ding, K. Zhang, F. Huang, and Y. Cao, Adv. Funct. Mat., vol. 23, pp.4255–4261, 2013; D.D.S. Fung, L. Qiao, W.C.H. Choy, C.C.D. Wang, W.E.I. Sha, F. Xie, and S. He, J. Mater. Chem., vol. 21, pp. 16349 – 16356, 2011. [3] X.H. Li, W.C. H. Choy, X. Ren, D. Zhang, H.F. Lu, Adv. Funct. Mat. DOI: 10.1002/adfm.201303384; X.H.Li, W.C.H.Choy, H.F. Lu, W.E.I. Sha, and H. P. Ho, Adv. Funct. Mat., vol.23, pp.2728–2735, 2013; X.H. Li, W. C.H. Choy, L Huo, F.X. Xie, W.E.I. Sha, B. Ding, X. Guo, Y. Li, J. Hou, J. You, Y. Yang, Adv. Mater. vol. 24, pp.3046-3052, 2012; X.H. Li, W. E.I. Sha, W.C.H. Choy, D.D.S. Fung, F. X. Xie, J. of Phys. Chem. C, vol. 116, pp.7200-7206, 2012; C.C.D. Wang, W. C. H. Choy, C. Duan, D.D.S. Fung, W.E.I. Sha, F.X. Xie, F. Huang, and Y. Cao, J. Mater. Chem., vol. 22, pp.1206–1211, 2012. [4] T.H. Zheng, W.C.H. Choy, and Y.X. Sun, vol. 19, pp.2648-2653, 2009; T.H. Zheng, W.C.H. Choy, and Y.X. Sun, Appl. Phys. Lett, vol. 94, 123303 (pp.3), 2009.