I am using two chambered MFC. I am getting OCV of 804 mV but maximum power density that the cell is able to achieve is only 5 mW/m2. What could be the possible reason for it?
If the open circuit voltage is relatively high and the the the harvested electric power is too low, it means that the short circuit current is too low. The fill factor may be also too low.
If you display you your dark and illuminated I-v curve one can diagnose your cell.
This book chapter may help you interpret your results:Chapter Solar cells and arrays: Principles, analysis and design
Also this paper may help you:Conference Paper Generic Analytical Models for Organic and Perovskite Solar Cells