In order to consider the effective structure of silicon solar cells for perovskite/silicon tandem solar cells, the optic and photovoltaic properties of textured and flat silicon surfaces were compared using mechanical-stacking-tandem of 2- and 4- terminal structures by perovskite layers on crystal silicon wafers.  The reflectance of the texture silicon surface in the range of 750-1050 nm could be reduced more than that of the flat silicon surface (from 2.7% to 0.8%), which resulted in increases in average IPCE values (from 83.0% to 88.0%) and current density (from 13.7 mA cm-2 to 14.8 mA cm-2).  Using the texture surface of silicon heterojunction (SHJ) solar cells, the significant conversion efficiency of 21.4% was achieved by 4-terminal device, which was 2.4%-up from that of SHJ solar cells alone.

And, for the progress of perovskite/silicon tandem solar cells, we introduce a totally vacuum-free cost-efficient crystalline silicon solar cells. Solar cells were fabricated based on low-cost techniques including spin coating, spray pyrolysis and screen-printing. A best efficiency of 17.51% was achieved by non-vacuum process with a basic structure of <AI/p+/p-Si/n+/SiO₂/TiO₂/Ag> CZ-Si p-type solar cells. J_SC and V_OC of the best cell were measured as 38.1 mAcm^-2 and 596.2 mV, respectively with FF of 77.1%. Suns-Voc measurements were carried out and the detrimental effect of the series resistance on the cell performance was revealed. It is concluded that higher efficiencies are achievable by the improvements of the contacts and by utilizing good quality starting wafers.

Finally, for the study of stability test on perovskite solar cells, Carbon-based triple-porous-layer perovskite solar cells without any hole transporting material were selected for investigation to reduce internal degradation issues about thermal stress.  The sealed perovskite solar cells which kept at 100 ˚C performed slow degradation in the power conversion efficiency until 4500 h, but the degradation speed was accelerated after that.  By analyzing the perovskite solar cells aged for 7000 h at 100 ˚C, the results of energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy suggest that, although Pb²⁺ and I- were sealed inside of the devices, the most of CH₃NH₃⁺ diffused out of the sealant UV-curable adhesive at 100 ˚C, which is the reason of the thermal degradation for the sealed perovskite solar cells.