TCO optimization of c-si heterojunction solar cells for tandem architecture by optical simulation

Silicon heterojunctions (Si HJs) are regarded as a promising structure to develop high efficiency tandem solar cells. However, the Si HJ structure has been optimized for use as single junction device and variations might be made in order to adapt it to tandem applications. In this work we analyse by optical simulations the improvements that could be achieved in the short circuit current of Si HJs used as bottom cell in tandem devices, if the front TCO layer is made thicker. This solution allows to adapt the absorption in the Si HJ to the incident light spectrum, that is rich of high wavelength photons if a wide band gap cell is put on top of the Si HJ. The investigation has been carried out for two top cell technologies: a high efficiency InGaP solar cell and a semitransparent perovskite solar cell. The improvement in JSC is of the order of 1 mA in both cases, and is more pronounced when the edge of transparency of the top cell occurs at higher wavelength.