Tin-doped indium oxide (ITO) sputtering is known as a damaging cause on organic hole transporting material in solar cells. In order to gain more insights into the reasons for poor device performance of perovskite solar cells by the ITO sputtering on Spiro-OMeTAD, here we present an in-depth study by I−V simulation analysis using corresponding equivalent circuit models. First, experimental I−V data were obtained for the perovskite solar cells with ⟨FTO/TiO 2 (dense)/ TiO 2 (mesoporous)/CH 3 NH 3 PbI 3 /Spiro-OMeTAD/ITO/Au⟩ configuration. An Au layer (t = 50 nm) was deposited on the ITO as a contact layer. The simulation studies indicated that sputtering of ITO onto Spiro-OMeTAD introduced a reverse Schottky diode and an additional diode to the device that could be relating the sputtering damage of the Spiro-OMeTAD layer. By considering the parameter of the reverse diode element as a function of sputtering time, it was found that the barrier height of the reverse Schottky diode was enhanced by the sputtering damage against Spiro-OMeTAD, which could be the key reason for the reduced fill factor of the devices.

Engineering of photonics for antireflection and electronics for extraction of the hole using 2.5 nm of a thin Au layer have been performed for two- and four-terminal tandem solar cells using CHNHPbI perovskite (top cell) and p-type single crystal silicon (c-Si) (bottom cell) by mechanically stacking. Highly transparent connection multilayers of evaporated-Au and sputtered-ITO films were fabricated at the interface to be a point-contact tunneling junction between the rough perovskite and flat silicon solar cells. The mechanically stacked tandem solar cell with an optimized tunneling junction structure was ⟨perovskite for the top cell/Au (2.5 nm)/ITO (154 nm) stacked-on ITO (108 nm)/c-Si for the bottom cell⟩. It was confirmed the best efficiency of 13.7% and 14.4% as two- and four-terminal devices, respectively.

Perovskite and textured silicon solar cells were integrated into a tandem solar cell through a stacking method. 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 two- and four-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 incident photon to current conversion efficiency values (from 83.0 to 88.0%) and current density (from 13.7 to 14.8 mA/cm). Using the texture surface of silicon heterojunction (SHJ) solar cells, the significant conversion efficiency of 21.4% was achieved by four-terminal device, which was an increase of 2.4% from that of SHJ solar cells alone.