June 22, 2007 SANYO has broken its own record for the world's highest energy conversion efficiency in practical size crystalline silicon-type solar cells. The company achieved this solar energy breakthrough by demonstrating an efficiency of 22% (beating a previous record of 21.8%) at a research level for its HIT solar cells, the first time that a photovoltaic manufacturer has broken through the 22% mark in conversion efficiency for this type of cell.
The increase in efficiency is concurrent with advances in lowering the production cost of the photovoltaic system and the reduction in the use of raw materials such as silicon.
The HIT (Heterojuncti n with Intrinsic Thin layer) solar cell is composed of a single thin crystalline silicon wafer surrounded by ultra-thin amorphous silicon layers. A “practical size” for such cells is defined as 100 cm2 or more. The structure of the HIT cell enables an improvement in the overall output by reducing recombination loss – a loss of electrical current that occurs when the negative electron and positive hole (carriers) that are produced within the solar cell combine and disappear. This is achieved by surrounding the energy generation layer of single thin crystalline silicon with high quality ultra-thin amorphous silicon layers. In its latest research SANYO developed special technologies for cleaning the energy generation layer and protecting it from damage during construction of the surrounding layer. The result was an increase in the open circuit voltage from 0.718V to 0.722V.
Improvements have also been made in the optical confinement technology. This involved the optimisation of the tiny uneven texture used on the cell surface to capture sunlight when it enters and minimize reflection.
SANYO is pushing forward with the expansion of its solar business after last year’s announcement of the "Next Generation Program for HIT Solar Cells" in which it aims more than triple its solar photovoltaic cell business by 2010 compared to 2005 levels. Further research is planned with the goal of applying this research-level achievement into mass production.
This news is among several recent breakthroughs in solar power including an alternative type of photovoltaic device using concentrated sunlight that has been demonstrated to an efficiency level of 40%. The challenge as we move toward a clean energy future is to find an balance between efficiency and manufacturing costs.