Charge transport in structural-ordering doped organic crystals: The effect of dye-doping concentration and crystal thickness on the mobility

- The mobilities of undoped (DSB) and doped (DSB⊂Tc, DSB⊂Pc) crystals have been measured.
- All the mobilities are in the same order of magnitude by FET and SCLC method.
- The structural-ordering retention is critical for the high mobility of doped crystal.
- The increase of crystal thickness is beneficial for improving the utilization of injected charges in the vertical-configuration diode.

Doped organic crystals with structural-ordering retention expected to the integration of high carrier mobility and high luminescence efficiency could be as promising materials for the high-performance light-emitting devices even the electrically pumped laser. In this work, charge-transport characteristics in doped organic crystals based on distyrylbenzene (DSB) as the host and tetracene (Tc) or pentacene (Pc) as the guest have been discussed in detail, including the effect factors of the guest doping concentration and the crystal thickness by the field-effect transistor (FET) and space-charge limited current (SCLC) methods. In the FETs, the mobilities of doped crystals have the slight decrease compared with that of undoped crystal but all are in the same order of magnitude (∼10−3-10−2 cm2/Vs), which is attributed to the structural-ordering retention even when the concentration of guest molecules embedded into the host crystal is up to ∼8%. Different with the lateral-configuration FET transporting the carriers inside several molecular layers of crystal surface, the vertical-configuration diode makes the carriers pass through the crystal body. The mobilities estimated by SCLC for doped and undoped crystals also present the similar variation with the FET's measurement. More significantly, the mobility increases with the crystal thickness at the same electrical field which indicates the negative influence of interfacial contact between the electrode and the crystal on the injected charges can be further suppressed by means of a relatively thicker crystal. Our primary results showcase that structural-ordering doped organic crystals have the comparable mobilities relative to their host sources, which is promising to extend to other doped crystal systems as well. Considering conveniently controllable properties of high efficiency and color-tunable emission by energy transfer, doped organic crystals are expected to be of interest for high-performance optoelectronic devices; moreover, it is verified that the increase of crystal thickness is beneficial for improving the utilization of injected charges in the vertical-configuration diode.

Charge-transport characteristics in doped organic crystals based on distyrylbenzene (DSB) as the host and tetracene (Tc) or pentacene (Pc) as the guest have been discussed in detail, including the effect factors of the guest doping concentration and the crystal thickness by the field-effect transistor (FET) and space-charge limited current (SCLC) methods. The mobilities of doped crystals are comparable to that of undoped crystal, attributed to the structural-ordering retention after the guest molecules embedding into the host crystal.109