Diagnostics and Process Monitoring Techniques for Solar Cell Production

During last several years, photovoltaic (PV) energy production and consumption have grown at a very rapid rate of about 40% per year, reaching one gigawatt per year. This has spurred an urgent need for process monitoring in the commercial production of solar cells to help improve yield and reduce the cost of PV energy. In the past, the PV industry has typically used minimal process monitoring,employing techniques that were developed for the microelectronics industry. However, there is a need for developing new diagnostic techniques specifically for PV production--techniques capable of high throughput, applicable to wafers with rough or textured surfaces, and with low operating cost. This paper will review various diagnostic techniques currently used in the PV industry for processcontrol, followed by new methods that are being developed, to be deployed in the PV industry in the near future. These techniques may be categorized into three groups: (i) measurement of physical parameters of wafers and cells, such as sawing quality, texture etching, diffusion for junction formation, antireflection coating, and metallization; (ii) measurement of electronic properties such asminority-carrier lifetime, process and material nonuniformities, and cell parameters; and (iii) other control parameters such as propensity for breakage of wafers and aesthetic appearance of cells and modules.