**2. Deposition techniques for single and multilayer thin films: description and advantages**

In the applications such as OPV or OLED, the heterostructures consist in one or more organic thin films (active material) sandwiched between two electrodes, an anode that must be transparent (in order to pass the light) and the metallic cathode [13].

The transparent electrode can be prepared by several techniques: sol‐gel, magnetron sputter‐ ing, oxygen ion beam assisted deposition, pulsed laser deposition (PLD), spray pyrolysis. The widely used methods are RF magnetron sputtering and PLD because films obtained by using these methods are characterised with adequate properties [36, 37].

In the case of the organic compounds, vacuum thermal evaporation (VTE) was one of the most used deposition techniques. Other methods such as spin‐coating, doctor blading or inkjet printing were also involved in the preparation of the organic layers [38–40].

The techniques used to prepare our organic heterostructures based on porphyrins and phthalocyanines are briefly described in the following section.

### **2.1. Transparent conductive oxide (TCO) thin films obtained by pulsed laser deposition (PLD)**

PLD is a versatile deposition method frequently used for the preparation of the thin films based on TCO materials [41]. The depositions are made inside a vacuum chamber. A solid target comprising the raw materials is ablated under a pulsed laser beam. When the elements from the target reach their evaporation temperature (above a certain value of the laser inten‐ sity), they are ejected from the target and form the plasma plume and pass to the deposition support starting the nucleation process which leads to the formation of the thin layer [42]. In order to improve the properties of the layers, the deposition can be also made in inert gases such as nitrogen (N2 ) or in reactive gas such as oxygen (O2 ). Also, the deposition target can be rotated during the deposition process to avoid a local deterioration which can affect the uniformity of the obtained film. The deposition parameters that must be controlled are flu‐ ence of the laser beam, a number of the laser pulses, target‐substrate distance and, sometimes, substrate temperature [41].

High‐quality TCO materials with an increased transmittance, low electrical resistivity and a reduced roughness of layer surfaces are obtained by PLD [37, 43].

### **2.2. Organic thin films prepared by vacuum thermal evaporation (VTE)**

VTE is a dry technique, frequently used for the deposition of the metallic layers, inorganic materials but also for the organic compounds. The method is simple and it can be applied for deposition on a large scale being used in the industry. Heliatek fabricated a cell made with three organic layers and high efficiency by VTE [7].

The solubility is another reason for choosing this deposition method which does not imply a solvent, if the organic materials are insoluble or poorly soluble. Thus, can be deposited suc‐ cessive organic layers, the previous deposited layer not being affected by the deposition of the next layer.

Using this method, materials can be evaporated which are vacuum compatible and chemi‐ cally stable up to their evaporation temperature. In the vacuum evaporation, the material of interest is heated until its vapour pressure is greater than 10−2 Torr [44]. The high vacuum in the deposition chamber ensures a particles flow (atoms, molecules) from the evaporated material. The process is followed by the condensation of the formed vapours on an ade‐ quate substrate [45]. As deposition substrates can be used glass, quartz, silicon, ITO or other plate materials.

The evaporation and condensation of the materials are influenced by the following param‐ eters: temperature of the heater (influences the evaporation rate), evaporation rate (depends by the system geometry), substrate temperature (control the surface atom mobility), heater and substrate geometry (related to film uniformity) and substrates (as smooth and clean as possible) [44]. All these parameters are very important because they affect the quality of the obtained thin film. It is known that the thin films have the tendency to copy the form of the substrate used for deposition.

The organic compounds adequate to be deposited by vacuum evaporation are those from the small molecules class, because they do not suffer stoichiometric changes during the transfer, having low melting temperatures (~300°C).

A disadvantage of this method is the time necessary until it is reached the high vacuum in the deposition chamber. But the thin films obtained are uniform, have a good adherence and have the wished geometry (shadow mask being used) [46].

#### **2.3. Organic thin films prepared by matrix‐assisted pulsed laser evaporation (MAPLE)**

The transparent electrode can be prepared by several techniques: sol‐gel, magnetron sputter‐ ing, oxygen ion beam assisted deposition, pulsed laser deposition (PLD), spray pyrolysis. The widely used methods are RF magnetron sputtering and PLD because films obtained by using

In the case of the organic compounds, vacuum thermal evaporation (VTE) was one of the most used deposition techniques. Other methods such as spin‐coating, doctor blading or inkjet

The techniques used to prepare our organic heterostructures based on porphyrins and

PLD is a versatile deposition method frequently used for the preparation of the thin films based on TCO materials [41]. The depositions are made inside a vacuum chamber. A solid target comprising the raw materials is ablated under a pulsed laser beam. When the elements from the target reach their evaporation temperature (above a certain value of the laser inten‐ sity), they are ejected from the target and form the plasma plume and pass to the deposition support starting the nucleation process which leads to the formation of the thin layer [42]. In order to improve the properties of the layers, the deposition can be also made in inert gases

be rotated during the deposition process to avoid a local deterioration which can affect the uniformity of the obtained film. The deposition parameters that must be controlled are flu‐ ence of the laser beam, a number of the laser pulses, target‐substrate distance and, sometimes,

High‐quality TCO materials with an increased transmittance, low electrical resistivity and a

VTE is a dry technique, frequently used for the deposition of the metallic layers, inorganic materials but also for the organic compounds. The method is simple and it can be applied for deposition on a large scale being used in the industry. Heliatek fabricated a cell made with

The solubility is another reason for choosing this deposition method which does not imply a solvent, if the organic materials are insoluble or poorly soluble. Thus, can be deposited suc‐ cessive organic layers, the previous deposited layer not being affected by the deposition of

Using this method, materials can be evaporated which are vacuum compatible and chemi‐ cally stable up to their evaporation temperature. In the vacuum evaporation, the material of

). Also, the deposition target can

these methods are characterised with adequate properties [36, 37].

phthalocyanines are briefly described in the following section.

**deposition (PLD)**

88 Phthalocyanines and Some Current Applications

such as nitrogen (N2

the next layer.

substrate temperature [41].

printing were also involved in the preparation of the organic layers [38–40].

**2.1. Transparent conductive oxide (TCO) thin films obtained by pulsed laser** 

) or in reactive gas such as oxygen (O2

reduced roughness of layer surfaces are obtained by PLD [37, 43].

three organic layers and high efficiency by VTE [7].

**2.2. Organic thin films prepared by vacuum thermal evaporation (VTE)**

MAPLE is a laser technique that has been developed from the PLD method. It was developed at the end of the 1990s from the necessity to deposit soft organic thin films (unicomponent layers or blends) preserving the properties of the used raw materials. MAPLE is also useful in the deposition of the polymers when the use of VTE results in the broken of the molecular chains [47, 48]. It is also used for the deposition of thin films from small molecule compounds or oligomers [49, 50].

In order to avoid the deterioration of the organic materials during the deposition were used lower laser fluences (<500 mJ/cm2 ) compared to those used in the classical PLD [47] and tar‐ gets (frozen in liquid nitrogen) formed from a mixture between the organic material and an adequate solvent used as a matrix [47, 48]. The solvent is chosen in order to obtain homo‐ geneous mixture with the organic material and to be compatible with the laser wavelength. The solvent evaporation takes place at the absorption of the laser energy that is converted in thermal energy. Further, the solvent is pumped outside from the deposition chamber by the vacuum system [48]. The material of interest reaches the support where the nucleation process starts and the thin layer is formed. The concentration of the target is usually ~3%, depending on the material type.

Multilayer organic heterostructure can be fabricated by MAPLE, because the second depos‐ ited layer does not affect the first obtained layer [51].
