Optimization of anti-reflective coatings for CIGS solar cells via real time spectroscopic ellipsometry

A new method combining in-situ real-time spectroscopic ellipsometry and optical modeling to optimize the thickness of an anti-reflective (AR) coating for Cu(In,Ga)Se2 (CIGS) solar cells is described and applied directly to fabricate devices. The model is based on transfer matrix theory with input from the accurate measurement of complex dielectric function spectra and thickness of each layer in the solar cell by spectroscopic ellipsometry. The AR coating thickness is optimized in real time to optically enhance device performance with varying thickness and properties of the constituent layers. Among the parameters studied, we notably demonstrate how changes in thickness of the CIGS absorber layer, buffer layers, and transparent contact layer of higher performance solar cells affect the optimized AR coating thickness. An increase in the device performance of up to 6% with the optimized AR layer is demonstrated, emphasizing the importance of designing the AR coating based on the properties of the device structure.

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Real-time monitoring and process control in amorphous∕crystalline silicon heterojunction solar cells by spectroscopic ellipsometry and infrared spectroscopy

Applied Physics Letters ◽

10.1063/1.1850612 ◽

2005 ◽

Vol 86 (3) ◽

pp. 032112 ◽

Cited By ~ 71

Author(s):

Hiroyuki Fujiwara ◽

Michio Kondo

Keyword(s):

Solar Cells ◽

Infrared Spectroscopy ◽

Process Control ◽

Real Time ◽

Spectroscopic Ellipsometry ◽

Crystalline Silicon ◽

Real Time Monitoring ◽

Heterojunction Solar Cells ◽

Silicon Heterojunction Solar Cells

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Materials and Interface Optimization of Heterojunction Silicon (HIT) Solar Cells Using in-situ Real-Time Spectroscopic Ellipsometry

MRS Proceedings ◽

10.1557/proc-808-a8.3 ◽

2004 ◽

Vol 808 ◽

Cited By ~ 6

Author(s):

D.H. Levi ◽

C.W. Teplin ◽

E. Iwaniczko ◽

R.K. Ahrenkiel ◽

H.M. Branz ◽

...

Keyword(s):

Solar Cells ◽

Real Time ◽

Spectroscopic Ellipsometry ◽

Crystalline Silicon ◽

Surface Recombination ◽

Chemical Vapor ◽

Energy Conversion Efficiency ◽

Open Circuit ◽

Analysis Tool

ABSTRACTWe have applied real-time spectroscopic ellipsometry (RTSE) as both an in-situ diagnostic and post-growth analysis tool for hydrogenated amorphous silicon (a-Si:H)/crystalline silicon (c-Si) heterojunction with intrinsic thin-layer (HIT) solar cells grown by hot-wire chemical vapor deposition. RTSE enables precise thickness control of the 5 to 25 nm layers used in these devices, as well as monitoring crystallinity and surface roughness in real time. Utilizing RTSE feedback, but without extensive optimization, we have achieved a photovoltaic energy conversion efficiency of 14.1% on an Al-backed p-type Czochralski c-Si wafer coated with thin i and n layers on the front. Open-circuit voltages above 620 mV indicate effective passivation of the c-Si surface by the a-Si:H intrinsic layer. Lifetime measurements using resonant coupled photoconductive decay indicate that surface recombination velocities can approach 1 cm/s. RTSE and transmission electron microscopy show that the intrinsic a-Si:H i-layers grow as a mixture of amorphous and nano-crystalline silicon.

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