**4.2.2 Thin -film deposition technique**

The thin film deposition of photovoltaic materials takes place by electron beam, resistance heating and sputtering techniques. These technologies differ from each other in terms of degree of sophistication and quality of film produced. A resistance-heated evaporation technology is relatively simple and inexpensive, but the material capacity is very small which restricts its use for commercial production line. Sputtering technique can be used to deposit on large areas and complex surfaces. Electron beam evaporation is the most versatile technique of vacuum evaporation and deposition of pure elements, including most metals, numerous alloys and compounds. The electron beam technology has an edge over its counterparts due to following merits of this technology:


### **4.2.2.1 e-Vap® thin film deposition technology**

Various frames of different electron beam sizes are offered by e-Vap® which are able to produce small research specimen to achieve commercial coating requirement with crucible

PSS film which is soluble in water becomes insoluble after treatment with EG. Raman spectroscopy indicates that interchain interaction increases in EG treated PEDOT: PSS by conformational changes of the PEDOT chains, which change from a coil to linear or expanded-coil structure. The electron spin resonance (ESR) was also used to confirm the increased interchain interaction and conformation changes as a function of temperature. It was found that EG treatment of PEDOT: PSS lowers the energy barrier for charge among the PEDOT chains, lowers the polaron concentration in the PEDOT: PSS film by w 50%, and increases the electrochemical activity of the PEDOT: PSS film in NaCl aqueous solution by w100%. Atomic force microscopy (AFM) and contact angle measurements were used to confirm the change in surface morphology of the PEDOT: PSS film. The presence of organic compounds was helpful to increase the conductivity which was strongly dependent on the chemical structure of the organic compounds, and observed only with organic compound with two or more polar groups. Experimental data were enough to make a statement that the conductivity enhancement is due to the conformational change of the PEDOT chains and the driving force is the interaction between the dipoles of the organic compound and dipoles

Photovoltaic thin film structures are more efficient in comparison to their planar

 Photovoltaic thin films offer increased surface area which is favourable for light trapping due to a reduction in specular reflectance but increased internal scattering,

 In Photovoltaic thin film structures, transport lengths for photoexcited carriers in the absorber are reduced and so electrons and holes do not need to travel over large

The thin film deposition of photovoltaic materials takes place by electron beam, resistance heating and sputtering techniques. These technologies differ from each other in terms of degree of sophistication and quality of film produced. A resistance-heated evaporation technology is relatively simple and inexpensive, but the material capacity is very small which restricts its use for commercial production line. Sputtering technique can be used to deposit on large areas and complex surfaces. Electron beam evaporation is the most versatile technique of vacuum evaporation and deposition of pure elements, including most metals, numerous alloys and compounds. The electron beam technology has an edge over its

possibilities of co-deposition and sequential deposition systems are available

precise film composition and cooler substrate temperatures can be maintained

Various frames of different electron beam sizes are offered by e-Vap® which are able to produce small research specimen to achieve commercial coating requirement with crucible

leading to increased optical path lengths for photon absorption.

on the PEDOT chains26.

counterparts.

Thin film PV structure offers following advantages 27-29:

distances before separation and collection.

counterparts due to following merits of this technology: precise control at low or high deposition rates is possible

uniform low temperature deposition is possible

 excellent material utilization is possible higher evaporation rates are possible freedom from contamination is possible

**4.2.2.1 e-Vap® thin film deposition technology** 

**4.2.2 Thin -film deposition technique** 

capacities from 2cc to 400cc. e-Vap® 100 miniature evaporation systems is a precise wire-fed electron beam source designed specifically for depositing monolayer thin films in ultrahigh vacuum environments capable to deposit metals at atomic level. e-Vap® 3000 and Caburn-MDC e-Vap® are other electron beam evaporation system of different capacity for a wide range of applications30. Various companies are working in the field of thin film photovoltaics as shown in Table 1.


Table 1. Photovoltaic thin film manufacturing
