Laser processing for thin film crystalline silicon solar cells

Abstract

Laser processing applied to thin film silicon is an interesting approach for solar cell fabrication. In this work, we investigate the effects of a continuous wavelength (CW) laser irradiation in solid phase or liquid phase of silicon on the structural and electrical properties of thin film silicon layers. Thus, results on CW laser induced crystallisation (LIC) of ultrathin amorphous silicon, laser induced epitaxy (LIE) of a thick amorphous silicon on a seed silicon layer, and laser induced thermal annealing (LIA) of polycrystalline silicon films are presented and discussed.

Improvement of Laser-Crystallized Silicon Film Quality via Intermediate Dielectric Layers on a Glass Substrate

“…In addition to e-beam crystallization method, laser crystallization (LC) is another method for use in LPC. 5,13,15,16,18−22 Especially, by using a continuous wave (CW) laser in LPC, crystalline domain size in the range of millimeters in width and up to centimeters in length on glass substrates was achieved. 13,20,22 Moreover, the defects and deformations of the substrates can be avoided or lowered and the choice of substrates and IDLs (buffer layers) can be diversified.…”

“…22 Additionally, the elevated substrate temperature can be used to avoid the crack formation through crystalline domains during the LC process and it can reduce thermally induced stress on the pc-Si layers. 5,16,22,24…”

“…The traditional way of producing pc-Si thin films is the solid-phase crystallization (SPC) method. However, SPC method has drawbacks of long annealing durations (∼24 h) and small grain size (∼1–3 μm), which result in high defect concentrations. , Rapid thermal annealing (RTA) is also a SPC method in which typically a halogen lamp is used to heat and crystallize a-Si thin films over glass substrates . The RTA process starts with a steep heating ramp (∼200 °C/s), which is followed by a steady temperature phase of ∼900 °C and finalizes with a cooling down (∼80 °C/s) phase, all maintained under an appropriate gas ambient .…”

“…However, SPC method has drawbacks of long annealing durations (∼24 h) and small grain size (∼1–3 μm), which result in high defect concentrations. , Rapid thermal annealing (RTA) is also a SPC method in which typically a halogen lamp is used to heat and crystallize a-Si thin films over glass substrates . The RTA process starts with a steep heating ramp (∼200 °C/s), which is followed by a steady temperature phase of ∼900 °C and finalizes with a cooling down (∼80 °C/s) phase, all maintained under an appropriate gas ambient . During these stages of the process, deformations occur on the glass substrates, which limits the choice of substrate materials .…”

“…The RTA process starts with a steep heating ramp (∼200 °C/s), which is followed by a steady temperature phase of ∼900 °C and finalizes with a cooling down (∼80 °C/s) phase, all maintained under an appropriate gas ambient . During these stages of the process, deformations occur on the glass substrates, which limits the choice of substrate materials . Aluminum-induced crystallization (AIC) of a-Si is another crystallization method that is carried out at relatively lower temperatures (<500 °C), and grain sizes (>10 μm) achieved using this method makes AIC pc-Si films suitable as seed layers for further crystallization techniques .…”