Application Of Rapid Thermal Processing In Crystalline Silicon Solar Cells

In this thesis, rapid thermal processing (RTP), a rapid and low-cost technique, was employed to fabricate mono-crystalline silicon solar cells. RTP was applied in the three important thermal processes, which were the p-n junction formation by phosphorous diffusion, thermal oxidation and contact formation. The electrode contacts were fabricated with the screen-printing technique, which was commonly used in the large-scale production lines. Up to now, a large area mono-crystalline silicon solar cell with high conversion efficiency has been fabricated successfully in domestic, and its conversion efficiency, open-circuit voltage, and short-circuit current density are 11%, 564.6 mV, and 30.7 mA/cm~2, respectively.Since the fabrication of emitters (p-n junctions) is a very important process in the whole solar cell fabrication processes, phosphorous diffusion in silicon has been extensively investigated. In the work, Spin-on-dopants (SOD), as dopants, thermally diffused in the rapid thermal processor with different dwell time, temperatures, and ambients. The behaviors of phosphorous diffusion in silicon were studied by Four-Point Probe (FPP), Spreading Resistance Profiles (SRP) and other equipments. The main research work and its achievements are as follows:1. Wet oxygen apparatus was developed by the author. Phosphorous diffusion in the RTP processor with different temperatures and ambients, including dry oxygen, wet oxygen and argon, was characterized by SRP and FPP. It was found that the RTP processor was not suitable for rapid thermal processing in the wet oxygen ambient and oxygen had an oxidation-enhanced-diffusion effect on the phosphorous diffusion in silicon under RTP as oxygen did in the conventional thermal process.2. After rapid thermal processing at 1050 ℃ and 900 ℃ with oxygen and argon ambients for different dwell time, the phosphorous diffusion was characterized by SRP and FPP. It was found that under RTP, the high energy photons' enhanced diffusion effect didn't dominate the diffusion process at 1050 ℃ in the oxygen ambient, while it did dominate the diffusion process at 900 ℃ either in oxygenambient or argon ambient.3. The dependence of phosphorous diffusion on the dwell time was researched by SRP and FPP after the samples were processed by RTP with different ambient, dwell time and temperatures. It was found that both the oxidation and high-energy photons could enhance the phosphorous diffusion under RTP.4. The mono-crystalline silicon solar cells with the conversion efficiency of 11% was fabricated by RTP.