Reliability Improvement and Remaining Issues on Photovoltaic Cells and Modules

Degradation phenomena of photovoltaic cells and modules were systematically and in detail studied by observing those exposed outdoors and subjecting those to various indoor acceleration tests. Those degradation phenomena were roughly classified into three categories; less incident light into photovoltaic cells, less collection of photogenerated carriers, and less photovoltaic ability itself. Degradation mechanisms of photovoltaic cells and modules were clarified by microscopic physical and chemical analyses. Based on the mechanisms, it was found that key materials for improving reliability are encapsulants and electrodes. Improvement methods of reliability for photovoltaic cells and modules were also proposed. Prediction of lifetime by indoor acceleration test methods is also important although the prediction is quite difficult using the artificial test methods with only one or two degradation factor(s). Remaining issues of reliability and durability will be also presented.