Charge carrier recombination in the ITO/PEDOT:PSS/MEH-PPV/Al photodetector

In this paper we investigate charge carrier recombination processes in polymer based photodetector ITO/PEDOT:PSS/MEH-PPV/Al. The major carriers are the hole polarons created by the photoexcitation in the active MEH-PPV film. The model used in this paper is based on the continuity equation and drift-diffusion equation for hole polarons. We assume the Poole-Frenkel expression for field dependence of the hole polaron mobility. The internal quantum efficiency dependence on incident photon flux density, incident light wavelength and applied electric field is included in the model. The simulated photocurrent density spectra for two different, assumed, recombination mechanisms, linear (monomolecular) and square (bimolecular) is compared with our experimental results. The bimolecular recombination mechanism applied in our model is assumed to be of Langevin type. The agreement between the measured and the calculated data unambiguously indicate that the hole polaron recombination mechanism in the MEH-PPV film is bimolecular with bimolecular rate constant depending on the external electric field. For the established recombination mechanism the theoretical prediction of the photocurrent density spectra shows excellent agreement with the measured spectra in wide range of inverse bias voltages (from 0 to -8 V). U radu su razmatrani rekombinacioni procesi u ITO/PEDOT:PSS/MEH-PPV/Al (ITO - Indium-Thin Oxide; PEDOT:PSS - poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate); MEH-PPV - poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) fotodetektoru. Vecinski nosioci naelektrisanja su supljinski polaroni nastali fotoekscitacijom unutar aktivnog MEH-PPV polimerskog filma. Izmereni spektar gustine fotostruje detektora poredjen je sa teorijski dobijenim spektrom za slucaj monomolekularne i bimolekularne rekombinacije nosilaca. Slaganje eksperimentalnih rezultata sa rezultatima proracuna nedvosmisleno ukazuju da se supljinski polaroni u polimerskom filmu rekombinuju bimolekularno, pri cemu koeficijent bimolekularne rekombinacije zavisi od jacine elektricnog polja. Za ustanovljeni tip rekombinacionih procesa modelovani spektar gustine fotostruje pokazuje odlicno slaganje sa eksperimentom u sirokom opsegu napona inverzne polarizacije (od 0 do -8 V).