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Relation between the electroforming voltage in alkali halide-polymer diodes and the bandgap of the alkali halide

Bory, B. F. ; Wang, J ; Gomes, H.L. ; Jassen, R.A.J. ; de Leeuw, D.D.M. ; Meskers, S.C.J.

Applied Physics Letters Vol. 105, Nº 23, pp. 233502 - 233502-4, December, 2014.

ISSN (print): 1077-3118
ISSN (online): 0003-6951

Scimago Journal Ranking: 1,86 (in 2014)

Digital Object Identifier: 10.1063/1.4903831

Electroforming of indium-tin-oxide/alkali halide/poly(spirofluorene)/Ba/Al diodes has been investigated by bias dependent reflectivity measurements. The threshold voltages for electrocoloration and electroforming are independent of layer thickness and correlate with the bandgap of the alkali halide. We argue that the origin is voltage induced defect formation. Frenkel defect pairs are formed by electron–hole recombination in the alkali halide. This self-accelerating process mitigates injection barriers. The dynamic junction formation is compared to that of a light emitting electrochemical cell. A critical defect density for electroforming is 1025/m3. The electro- formed alkali halide layer can be considered as a highly doped semiconductor with metallic trans- port characteristics.