We investigated semiconductor direct wafer bonding in a regular, non-cleanroom environment to understand environmental influences on bonding characteristics. The correlations among surface treatments, particle densities, bonding strengths, and interfacial conductivities were systematically investigated. On the basis of our investigation and condition optimization, we realized direct semiconductor bonding in the regular atmosphere with high interfacial mechanical stabilities and electrical conductivities, sufficient for device applications. Furthermore, we demonstrated fabrication and operation of solar cells using the developed bonding technique, with current paths across the bonded interfaces. These results and related technical insights may be useful for a low-cost, simpler manufacture of high-performance electrical and optical devices.

A systematic investigation has been made on output measurement of the a-Si//al-SiGe//a-SiGe triple stacked solar cells. Prototype modules incorporating triple a-Si cells fabricated in high deposition rate plasma CVD process with micro-wave power source[l] have been exposed outdoor for about a half to one year at three different geographical locations to evaluate the outdoor performance under cold, temperate and tropical climates. The results showed that a-Si performed better under higher temperature climate. Energy efficiency over 8% was obtained in Kuala Lumpur. Power rating under 1 sun, 50deg.C light soaking condition seems to be reasonable in Kyoto.

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