[PDF]    http://dx.doi.org/10.3952/lithjphys.46218

Open access article / Atviros prieigos straipsnis

Lith. J. Phys. 46, 237–243 (2006)


ROLE OF MOLECULAR CHAIN ORIENTATION ON CARRIER TRAPPING AND TRANSPORT EFFECTS IN POLYMER BLENDS
V. Kažukauskas and V. Čyras
Faculty of Physics and Institute of Materials Science and Applied Research, Vilnius University, Saulėtekio 9, LT-10222 Vilnius, Lithuania
E-mail: vaidotas.kazukauskas@ff.vu.lt

Received 11 February 2006

We have investigated carrier trapping and transport effects influenced by molecular chain orientation in the samples of poly(9-vinylcarbazole) (PVK) doped with 30% wt 4-dibutylamino-4′-nitrostilbene (DBANS). The orientation of polar DBANS molecules was achived by applying the electric field above the glass transition temperature; and its effect was investigated by means of Thermally Stimulated Currents (TSCs) method and current–voltage (I–V) characterization. We demonstrate that the molecular chain orientation causes significant changes both in I–V dependences and the TSC spectra. Changes of the TSCs induced by orientation were best expressed in the temperature range of 280–290 K. They could be attributed to the thermally activated process with activation energy of about 0.38 eV.
Keywords: carrier transport and trapping, polymers PVK and DBANS, molecular chain orientation
PACS: 72.80.Le, 73.50.Gr, 73.61.Ph, 81.40.Rs


MOLEKULINIŲ GRANDŽIŲ ORIENTACIJOS ĮTAKA KRŪVININKŲ PERNAŠAI IR PAGAVIMUI POLIMERŲ MIŠINIUOSE
. V. Kažukauskas, V. Čyras
Vilniaus universitetas, Vilnius, Lietuva

Buvo tirtos polivinilkarbazolo – PVK (angl.: poly(9-vinylcarbazole)), papildyto 30% masės santykiu DBANS (4-dibutylamino-4′-nitrostilbene) polimeru krūvio pernašos ir pagavimo ypatybės, priklausomai nuo DBANS polinių molekulių grandžių erdvinės orientacijos. Molekulės buvo orientuojamos išoriniame elektriniame lauke 394 K temperatūroje. Prijungus įtampą laidumo kryptimi, buvo sukurtas poliarizacijos laukas užtvarine kryptimi, ir atvirkščiai. Taip orientavus bandinio molekules, buvo matuojamos voltamperinės charakteristikos (I–V) ir šiluma skatinamųjų srovių (ŠSS) spektrai. Įrodyta, jog molekulių grandžių orientacija turi lemiamą įtaką I–V kreivės formai žemiau 250 K temperatūros. Taip pat gauti ryškūs ŠSS skirtumai, kuriems išanalizuoti buvo atliekamas ŠSS modeliavimas, atsižvelgiant tiek į krūvininkų šiluminę generaciją iš pagavimo lygmenų, tiek į krūvininkų judrio kitimą, nusakomą Gauso netvarkos (Gaussian disorder) bei Pulio ir Frenkelio (Poole–Frenkel) empiriniais modeliais.
Temperatūros srityje nuo 166 iki 240 K efektinė ŠSS aktyvacijos energija tebuvo apie 0,037 eV. Tokios mažos vertės aiškintinos ne krūvininkų tankio, bet jų judrio kitimu. Tai įrodo, jog polimeruose krūvininkų judris priklauso nuo išankstinio sužadinimo. ŠSS pokyčiai dėl DBANS molekulių orientacijos buvo ryškiausi temperatūros intervale nuo 280 iki 290 K. Skaitmeninė analizė parodė, jog šie pokyčiai susiję su vienu termiškai aktyvuotu procesu, kurio aktyvacijos energija yra apie 0,38 eV. Kai temperatūra didesnė nei maždaug 310 K, gautas srovės augimas, pasižymintis maždaug 0,9 eV aktyvacijos energija, kuris gali būti dėl krūvininkų šiluminės aktyvacijos per vieno iš bandinio kontaktų potencialinį barjerą.


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