One-sun, single-crystalline silicon solar cell research

The point-contact solar cell design, the most efficient silicon concentrator solar cell design to date, is explored for use in one-sun applications. The necessary modifications to backside-contact concentrator cell design for operation at one-sun are explored and implemented. Large-area, point-contact solar cells were fabricated on n- and p-type substrates in low-level injection (LLI). The characteristics of these LLI cells were compared to those of four different architectures of cells with substrates in high-level injection (HLI). Both types of cell achieved open-circuit voltages over 700 mV at one-sun, LLI cells had higher fill factors, and HLI cells had substantially higher short-circuit currents. The mechanisms responsible for these observations are discussed. The high V(sub oc) and J(sub sc) of the HLI cells combine to make them more efficient than the LLI cells, with efficiencies measured at Sandia up to 22.7 percent for a 37.5 sq cm cell at one sun. This is the highest one-sun efficiency for a silicon cell larger than 4 sq cm. Simplified, backside-contact solar cell processes were also developed, which have nearly 100 percent yield. Over 80 such cells, each with a 35-sq cm area or greater, were delivered to Sandia. Cells made with these simplified processes had efficiencies up to 21.3 percent for a 37.5-sq cm cell. The recombination properties of Si3N4b layers over SiO2 were characterized, since Si3N4 is an excellent antireflection coating for cells laminated under glass. Several prototype flat-plate modules of backside-contact cells were built, with up to 24 cells and efficiencies up to 19 percent.