Artificial photosynthetic monolithic devices using voltage-matched perovskite/silicon tandem photovoltaic modules

Abstract

We designed monolithic devices consisting of photovoltaic (PV) modules directly connected to electrochemical (EC) reactor modules for artificial photosynthetic H2 and CO production. Double-junction (2J) PV cells commonly used for this purpose suffer from current mismatching between the top and bottom cells under solar spectrum variation; the detrimental impacts on the solar-to-H2 and -CO energy conversion efficiencies ( ηH2 and ηCO, respectively) were found to be more serious than those on solar-to-electricity conversion efficiencies of solar cells connected to power conditioners, because the power conditioners always optimize the operating voltages. To solve this problem, we adopted the combination of a voltage-matched (VM) tandem PV module and an EC module in which multiple EC reactors are series-connected. Parallel connection of the top and bottom PV modules eliminates the current mismatching problem involved in 2J PV cells, while series-connected multiple top PV cells, bottom PV cells, and EC reactors in these modules, respectively, secure voltage matching among these modules. We adopted organic–inorganic hybrid perovskite (PVK) top cells and crystalline silicon (Si) bottom cells according to another design strategy of widespread use. Thus, we modeled the artificial photosynthetic operation of the monolithic devices based on the properties of state-of-the-art PVK and Si PV cells and H2- and CO-producing EC reactors and evaluated annually averaged ηH2 and ηCO. The newly designed monolithic devices using the VM tandem PV modules improve ηH2 compared to those of the conventional devices using 2J PV cells, from 23% to 29%, and ηCO from 23% to 27%.