Semi-Transparent Amorphous Silicon Solar Cells on Inexpensive Plastic Substrates
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0973-BB06-01
Semi-Transparent Amorphous Silicon Solar Cells on Inexpensive Plastic Substrates Ilvydas Matulionis1,2, Jian Hu1, Alex Stavrides1, Nathan Call1,2, Augusto Kunrath1, and Arun Madan1,2 1 MVSystems, Inc., 500 Corporate Circle, Suite L, Golden, CO, 80401 2 Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, CO, 80401 ABSTRACT We report a monolithic series connected semi-transparent (transmission > 40%) amorphous silicon (a-Si:H) solar cell panel (substrate area 30cm × 40cm), which has an ilayer thickness 3% constructed on inexpensive plastic substrates.
INTRODUCTION Crystalline Si/poly-crystalline Si solar cells presently dominate the photovoltaic market. Due to a low conversion efficiency, η, ( 40%) a-Si:H solar cell panel (substrate area 30 × 40 cm2), with an i-layer thickness < 2000 Å and an active area η ~ 3%. We have successfully fabricated laser scribed series connected mini-modules (area up to 20 cm2) on glass and plastic substrates with an aperture area η >3%. In addition, we are currently building a reel-to-reel cassette cluster tool system with a web width of 30 cm to accommodate inexpensive plastic substrates which could be used to construct such semi-transparent panels.
EXPERIMENTAL a-Si:H films and solar cells/panels were produced in a commercially available PECVD cluster tool system specifically designed for the thin film semiconductor market and manufactured by MVSystems, Inc. The samples were prepared on a 30 x 40 cm² substrate carrier
situated on the anode side of the RF electrode assembly. Deposition conditions were: RF power 20-60 Watt, an anode-cathode distance of 1-6 cm, flow rate of silane 2-30 sccm, flow rate of hydrogen 10-100 sccm, deposition pressure 100-700 mTorr, and Ts < 150°C. The p+-layer consisted of a-SiC:H:B and was deposited from SiH4, CH4 and B2H6 gas mixtures, while the n+layer was prepared using a SiH4 and PH3 gas mixture. ITO and ZnO materials were sputtered from InSnO2 and Al doped ZnO targets, respectively. The opto-electronic properties of single aSi layers were characterized by photo (σph) and dark (σD) conductivity and the band gap Eg was determined using Tauc’s plot. RESULTS AND DISCUSSION As plastics are generally hygroscopic, out-gassing from the material can lead to oxygen and water in the vacuum chamber which then contaminate the a-Si:H films; hence prior to the deposition, the plastic substrates were cleaned and degassed in vacuum within the cluster tool for a specific period of time at an elevated temperature. In Table I, we first consider the properties of n+ and p+ type layers when the deposition temperature, Ts, is lowered to below 150°C. Even though the n+-layer showed very similar electrical properties on glass and plastic Table I. Comparison of p+ and n+-layer properties on glass and inexpensive plastic (IP) substrates.
σD (S/cm)
σph (S/cm)
Eg (eV)
Glass
3.4·10-6
5.5·10-6
2.03
IP Glass IP
6.0·10-7 8.7·10-4 3.5·10-4
1.3·10-6 1.3·10-3 6.5·10-4
1.93
Layer Substrate p
+
n+
substrates, the dark condu
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