**5. TCO layers deposited by PLD on flat and nanopatterned glass substrates for developing organic heterostructures**

The TCO films (ITO and AZO) deposited by PLD on flat and nanopatterned glass substrates were used for developing organic heterostructures for optoelectronic applications. Schematic representation of two organic heterostructures and their I-V characteristics are given in **Figure 10**: one based on adenine (Ade), the nucleic acid base film being deposited on ITO by vacuum thermal evaporation [103], and another based on N,N′-di(1-naftalenil)-N,N′-diafenil-(1,1′-bifenil)-4,4′-diamina (α-NPD), 1,4-bis [4-(N,N-diphenylamino)phenylvinyl] benzene (P78) and 4,7 diphenyl-1,10-phenanthroline (BPhen), the three stacked organic films being deposited on AZO by matrix-assisted pulsed laser evaporation (MAPLE) [86]. For both organic structures, aluminum electrode (100 nm) was deposited by vacuum thermal evaporation.

Hence, in the case of adenine deposited on ITO/glass substrate, the I-V characteristic (recorded in dark between −1 V and 1 V applied voltage) is changed from linear (at small voltage) to nonlinear at higher voltage (>0.5 V) probably due to the different properties shown by the contacts ITO/adenine and adenine/Al [103]. Regarding

#### **Figure 10.**

*Schematic representation of the organic structures using TCE deposited by PLD on flat and nanopaterned glass substrates and I-V characteristics recorded on representative organic structures (single organic film – blue curve and three stacked organic films – green curve).*

#### *Pulsed Laser Deposition of Transparent Conductive Oxides on UV-NIL Patterned Substrates… DOI: http://dx.doi.org/10.5772/intechopen.105798*

the electrode patterning, it is expected that this effect induces some changes in the electrical properties of the investigated structures by modifying the electrical field, which in turn can affect the charge carrier transport and their collection [104]. The scattering/recombination processes can be influenced by (i) the enlargement of the contact area between the nanopatterned TCO and the organic film, (ii) the change in the pathway of the charge carriers to the electrodes due to the presence of pillars; and (iii) the morphology of films characterized by grain boundaries. Compared with the structure prepared on ITO/glass electrode, the shape of the I-V characteristic of the structure deposited on ITO/NP-glass electrode was changed into a very close rectifying diode behavior. At small voltage, a slow increase in the current value is noted at the same time with the voltage increase, while a faster increase in the current is obtained after 0.5 V probably due to the growth of the number of electrons that cross the barrier and are more easily collected to the patterned electrode [103].

Concerning N,N′-di(1-naftalenil)-N,N′-diafenil-(1,1′-bifenil)-4,4′-diamina, 1,4-bis [4-(N,N-diphenylamino)phenylvinyl] benzene and 4,7 diphenyl-1,10-phenanthroline, an OLED-type structure was practically obtained using a hole transport layer (α-NPD), an emissive film (P78), and an electron transport layer (BPhen), respectively. Hence, the I-V characteristic plotted for the structure prepared on AZO/ glass electrode presents a diode behavior. The structure fabricated on AZO/NP-glass electrode evidenced an improvement in the current value (at 1 V), meaning that the electrode patterning influences positively the electrical properties of the organic structures obtained on it [86], the charge transport being favored by the enlargement of the contact area between the nanopatterned AZO and the organic films [35]. This improvement recorded in the current value could be reflected in the final performances of the organic device fabricated on this type of nanostructured TCO.

Consequently, the optical and electrical properties of the organic structures fabricated on nanopatterned transparent electrodes can be enhanced due to the nanopatternation process. Taking into consideration that the organic heterostructures developed on TCO substrates are already part of our daily life (Heliatek company develops projects based on OPV solar films that can be attached in different locations or building facades or roofs [105], and LG Display produces OLED TV panels offering its OLED panels to other companies such as LG Electronics, Sony, Vizio, and Panasonic [106]), the organic layers deposited on patterned TCO can be also applied in the field of the organic optoelectronic devices.
