**4.2 Laser processing for thin-film (TF) photovoltaic**

The serial monolithic interconnection of thin-film solar cell can be achieved by laser scribing three patterns during fabrication. The layers are numbered in the order in which they are deposited. They are micromachined by laser ablation, an established material removal process [35].

Nayak et al. [37] reported nanocrystalline Si material following femtosecondlaser-induced crystallization of a-Si:H. Despite the number of structural defects, which for the time being prohibits PV applications, the process produces remarkable light-trapping microstructures at the surface.


#### **Table 1.**

*Various Texturing Methods and Reflectivity values reported for mono-crystalline (c-Si) and multi-crystalline (mc-Si) wafers (Adapted/modified from references [32, 36–42]).*

**431**

silicon solar cell.

*Advanced Laser Processing towards Solar Cells Fabrication*

**4.3 Light trapping for thin silicon solar cells by femtosecond laser** 

A variety of surface morphologies can be obtained from fs laser treatments, depending on laser parameters and the ambient gas environment. The efficacy fs laser texturing of solar cell devices is also demonstrated in ref. 26 and the problem of laser-induced damage may have significantly improved cell performance in the future by increased absorption (vs. un-textured cells) for infrared photons, due to

**4.4 Patterning of transparent conducting oxide (TCO) layers by femtosecond** 

A method for patterning crystalline indium tin oxide (c-ITO) patterns on amorphous indium tin oxide (a-ITO) thin films is proposed by femtosecond laser irradiation at 80 MHz repetition rate. The laser patterning technique provides a versatile and highly precise means of fabricating the transparent electrode structures required in a wide range of modern optoelectronic devices. High repetition rate femtosecond (80 MHz) laser-induced crystallization and proposed laser patterning technique provides a versatile and highly precise means of fabricating TCO

**4.5 Femtosecond laser induced crystallization & simultaneous formation of** 

Femtosecond laser induced crystallization & simultaneous formation of lighttrapping nanostructures is a one-step laser process, which could lead to fabricate the highly efficient solar cells [42–51]. Mmicrostructures and small spikes have been spontaneously formed upon laser treatment. Interestingly the a-Si:H films turned completely dark from an original shiny reddish gray color. A similar effect has been extensively studied by Mazur's group and others in crystalline bulk silicon wafers

Solar cells based on laser-modified materials focus on three major thrusts that will lead to more efficient and economic thin-film solar cell fabrication by (i) combining femtosecond laser irradiation processing of a-Si:H surface and simultaneous crystallization occurs in a one step process [16]. Optical absorption will be enhanced by light trapping via multiple reflections through the surface geometry changes, and the formation of mixture of μc-Si:H and a-Si:H after crystalline suggests that the overall stability will be potentially increased; (ii) Laser with a shorter, femtosecond pulse duration will be applied for nano-structuring of TCO deposited on glass as a plasmonic nanostructure for efficient light trapping; (iii) For scribing thin-film solar cells with femtosecond laser will be applied for electrical isolation, hermetic sealing of the module, glass cutting, the complete removal of all layers from the edges of fully processed thin-film solar cells on glass substrates [52]. **Figure 5** is a schematic presentation of how femtosecond laser irradiated silicon can be incorporated into the p-i-n configuration of a thin-film

*DOI: http://dx.doi.org/10.5772/intechopen.94583*

**texturing**

enhanced light-trapping.

**laser**

structures [42].

[42–52].

**light-trapping nanostructures**

**5. Solar cells based on laser-modified materials**

*Solar Cells - Theory, Materials and Recent Advances*

self-assembled micro/nano structures are formed [32].

**4.2 Laser processing for thin-film (TF) photovoltaic**

established material removal process [35].

light-trapping microstructures at the surface.

Zechner et al*.* 1997 Mechanical

Abbott et al*.* 2006 Laser

Younkin et al*.* 2003 Femtosecond

Nayak et al*.* 2010 Ultrafast laser

*(mc-Si) wafers (Adapted/modified from references [32, 36–42]).*

Gangopadhay et al*.*

**Author Year Technique Substrate** 

2017 Isotropic acidic

texturing

grooving

texture

laser-induced microstructure

> micro/nano structure

Inomata et al*.* 1997 RIE mc-Si c-Si & mc-Si <2 Vazsonyi et al*.* 1999 NaOH+IPA c-Si c-Si 10 Nashimoto et al*.* 2000 Na2O3 c-Si c-Si 10

Nishioka et al*.* 2009 Ag nanoparticle c-Si c-Si & mc-Si <5 Branz et al*.* 2009 Au nanoparticle c-Si c-Si & mc-Si <2

*Various Texturing Methods and Reflectivity values reported for mono-crystalline (c-Si) and multi-crystalline* 

**Table 1** compares various texturing methods and reflectivity values reported for c-Si and mc-Si wafers. While anisotropic chemical etching method using KOH or NaOH with IPA is applicable for c-Si materials, it could not be applied to multicrystalline materials due to the anisotropic nature of the chemical etchant. Isotropic chemical texturing uses acidic mixture of HF and HNO3 and organic additives for multi-crystalline silicon (mc-Si). On the other hand, lasers are unique energy sources and laser ablation is an isotropic process. Lasers could texture surfaces by selectively removing materials by ablation process. Texturing could be achieved irrespective of the crystallographic orientation of material surface. Under shorter pulse regimes (few nanoseconds to femtoseconds), a very different types of

Total reflection of as-laser-treated samples is very low and increases by a few

The serial monolithic interconnection of thin-film solar cell can be achieved by laser scribing three patterns during fabrication. The layers are numbered in the order in which they are deposited. They are micromachined by laser ablation, an

Nayak et al. [37] reported nanocrystalline Si material following femtosecondlaser-induced crystallization of a-Si:H. Despite the number of structural defects, which for the time being prohibits PV applications, the process produces remarkable

**used**

**Applicable to Approx.**

mc-Si mc-Si 15

mc-Si c-Si & mc-Si >15

c-Si c-Si & mc-Si <5

c-Si c-Si & mc-Si <3

and thin a-Si

c-Si c-Si, mc-Si,

**R (%) @550 nm (as textured)**

<3

more percentages after post-chemical cleaning as shown in reference [42].

**430**

**Table 1.**
