Nonconjugated Anionic Polyelectrolyte as an Interfacial Layer for the Organic Optoelectronic Devices

• Published in: ACS applied materials & interfaces Vol. 5; no. 14; pp. 6508 - 6513
• Main Authors: Lim, Gyeong Eun, Ha, Ye Eun, Jo, Mi Young, Park, Juyun, Kang, Yong-Cheol, Kim, Joo Hyun
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24-07-2013
• Subjects: nonconjugated anionic polyelectrolyte; electron transporting/injecting layer; optoelectronic device; electrical contact resistance; interface dipole; interfacial layer
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/am400478b

A nonconjugated anionic polyelectrolyte, poly­(sodium 4-styrene­sulfonate) (PSS-Na), was applied to the optoelectronic devices as an interfacial layer (IFL) at the semiconducting layer/cathode interface. The ultraviolet photoelectron spectroscopy and the Kelvin probe microscopy studies support the formation of a favorable interface dipole at the organic/​cathode interface. For polymer light-emitting diodes (PLEDs), the maximum luminance efficiency (LEmax) and the turn-on voltage (V on) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL were 3.00 cd/A and 5.5 V, which are dramatically improved than those of the device without an IFL (LEmax = 0.316 cd/A, V on = 9.5 V). This suggests that the PSS-Na film at the emissive layer/cathode interface improves the electron injection ability. As for polymer solar cells (PSCs), the power conversion efficiency (PCE) of the device with a layer of PSS-Na spin-coated from the concentration of 0.5 mg/mL was 2.83%, which is a 16% increase compared to that of the PSC without PSS-Na. The PCE improvement is mainly due to the enhancement of the short-circuit current (12% increase). The results support that the electron collection and transporting increase by the introduction of the PSS-Na film at the photoactive layer/cathode interface. The improvement of the efficiency of the PLED and PSC is due to the reduction of the Schottky barrier by the formation of a favorable interface as well as the better Ohmic contact at the cathode interface.