**5. Conclusions**

**Figure 20.** Current‐voltage characteristics (in dark conditions—curves 1 and under illumination—curves 2) of the organic heterostructures deposited by MAPLE: PET/ITO/ZnPc/TPyP/Al (a), PET/ITO/MgPc/TPyP/Al (b), PET/ITO/

**Figure 21.** Current‐voltage characteristic (under light, −1 V–1 V domain) of the PET/ITO/ZnPc:TPyP/Al heterostructure

ZnPc:TPyP/Al (c) and PET/ITO/MgPc:TPyP/Al (d) structures.

108 Phthalocyanines and Some Current Applications

deposited by MAPLE.

Heterostructures based on ZnPc were prepared using two different deposition techniques. In a first step, ZnPc was deposited into a multilayer structure in combination with C60 and NTCDA by VTE, the most accessed method for the deposition of organic materials.

The heterostructure were fabricated starting from glass/ITO or glass/ITO covered by a thin film of PEDOT:PSS on which were deposited ZnPc, C60, NTCDA and Al electrode or starting from glass/Al, followed by the deposition of NTCDA, C60, ZnPc and ITO electrode. The struc‐ tures present the absorption maxima characteristic to the used materials. It was evidenced that the way in which the layers are deposited influenced the properties. *I*‐*V* characteristics revealed that the value of the current is increased in normal configuration glass/ITO/ZnPc/ C60/NTCDA/Al when an additional PEDOT:PSS layer is used. An increase in the current value was also achieved depositing the layers in inverted order (glass/Al/NTCDA/C60/ZnPc/ITO).

A p‐n heterostructure based on ZnPc and NTCDA layers was also fabricated by a laser technique. Moreover, the structures are obtained on the AZO substrate, and a TCO used to replace the ITO, the material most used as a transparent conductor electrode. AZO layers with adequate optical and electrical properties were prepared by PLD. The influence of an oxygen plasma treatment of AZO on the properties of the organic structures deposited on this TCO was analysed. The UV–VIS spectra show features typical to the used materials, cover‐ ing a large region of the visible domain. The PL emission bands attributed to the ZnPc and NTCDA were overlapped by the emission bands showed by the AZO substrate. AFM images evidenced a decrease in the size of the grains of the organic heterostructures with the increase in duration of the applied plasma treatment of the AZO substrate. The *I*‐*V* characteristics of the heterostructures revealed an injector contact behaviour and the appearance of the space charge limited currents (characteristic in organic materials) at voltages higher than 0.4V. AZO substrates treated in oxygen plasma (for 5 and 10 min) can favour the injection of the charge carrier in the organic layer, probably as a result of the increasing of AZO work function (lead‐ ing to a decrease in the energetic barrier at the interface), and determining a current higher with 1 order of magnitude in the heterostructures prepared on the treated substrate.

Organic heterostructures based on metal phthalocyanines and a porphyrin (ZnPc orMgPc and TPyP) were deposited by MAPLE on flexible substrate PET/ITO (in stacked or mixed form). The films preserve their IR absorption properties indicating that no decomposition appears at the laser transfer. The *I*‐*V* characteristics of the heterostructures measured in dark conditions show an increased current value with 3 orders of magnitude higher for the struc‐ ture with MgPc:TPyP compared to the structure formed with stacked films based on the same compounds. The appearance of the photovoltaic effect was remarked in the heterostructures with ZnPc:TPyP when the structure was exposed to the light.

In conclusion, thin films based on porphyrins and/or phthalocyanines can be deposited in multilayers or blend configurations on various substrates (ITO/glass, AZO/glass, Al/glass or ITO/PET) by different deposition techniques, including laser techniques. The obtained results are promising and very useful for further applications in the photovoltaic field.
