Influences of deposition parameters on micro-crystalline silicon single junction cell efficiency in large-area and high rate deposition

Abstract

For the mass production of silicon thin film solar cell, it is a key issue to increase deposition rate of microcrystalline silicon film on a large area substrate. One of the most effective methods to increase deposition rate of the film is using high frequency and high power plasma. However, high frequency plasma leads to plasma non uniformity in large area deposition, and high power plasma induces substrate heating during deposition of microcrystalline silicon film and degrades the film quality. In this study, we developed a shaped electrode for spatially uniform plasma and a susceptor cooling system for preventing substrate heating by plasma. And also we investigated the influences of deposition parameters on the microcrystalline silicon single junction cell efficiency with high frequency and high power plasma. Glass substrate was 1.1 m × 1.3 m and plasma excitation frequency was 40 MHz. Capacitively coupled parallel plates RF reactor with concave shaped electrode was used. For the high deposition rate of the microcrystalline films, plasma powers of 0.8∼1.1W/cm2 were used. The highest deposition rate of microcrystalline silicon was 2nm/s. The increases of temperature of susceptor were monitored by two thermocouples which were installed at center and outer side of the susceptor. The temperature increases were suppressed to almost zero with liquid cooling systems. Multiple step deposition was performed which means the higher H2/SiH2 ratio at the initial stage of film growth was used and the ratio gradually decreased during deposition in order to eliminate the amorphous layer at the interface between substrate and film. We also achieved microcrystalline single junction cell efficiencies above 6% on large area substrate at high deposition rate of 1.5nm/s.