Thin film silicon solar cells by AIC on foreign substrates

This paper presents the fabrication of thin film crystalline silicon solar cells on foreign substrates like alumina, glass–ceramic (GC) and metallic foils (ferritic steel—FS) using seed layer approach, which employs aluminium induced crystallisation (AIC) of amorphous silicon. Effect of hydrogen content in a-Si:H precursor films on the AIC process has been studied and the results showed that defects in the AIC grown films increased with increase of hydrogen content. At the optimal thermal annealing conditions, the AIC grown poly-Si films showed an average grain size of 7.6, 26, and 8.1 μm for the films synthesised on alumina, GC, and FS, respectively. The grains were (1 0 0) oriented with a sharp Raman peak around 520 cm−1. Similarly, n-type seed layers were also fabricated by over-doping of as-grown AIC layers using a highly phosphorus doped glass solution. The resistivity of as-grown films reduced from 8.4×10−2 Ω cm (p-type) to 4.1×10−4 Ω cm (n-type) after phosphorus diffusion. These seed layers of n-type/p-type were thickened to form an absorber layer by vapour phase epitaxy or solid phase epitaxy. The passivation step was applied before the heterojunction formation, while it was after in the case of homojunction. Open circuit voltage of the junctions showed a strong dependence on the hydrogenation temperature and microwave (μW) power of electron cyclotron resonance (ECR) plasma of hydrogen. Effective passivation was achieved at a μW power of 650 W and hydrogenation temperature of 400 °C. Higher values of solar conversion efficiencies of 5% and 2.9% were achieved for the n-type and p-type heterojunction cells, respectively fabricated on alumina substrates. The analysis of the results and limiting factors are discussed in detail.

Graphical AbstractIlluminated current-voltage (I-V) curves of p- and n-type poly-Si solar cells on alumina substrate.Figure optionsDownload as PowerPoint slideResearch highlights
► For the first time, we have reported the effect of hydrogen content in PECVD deposited a-Si precursor films on the microstructural quality of the seed layer grown by aluminium induced crystallisation (AIC) and synthesis of poly-Si seed and base layers on metallic substrates.
► Interesting results on n-type seed layers and high temperature epitaxy of the seed layer were obtained.
► A record efficiency of 5% has been achieved for n-type polycrystalline solar cells on alumina substrates.