On Perimeter Losses in Perovskite Top‐ and Poly‐Si‐Passivated Silicon Bottom Cells: Do Small Area Tandems Reveal the Full Efficiency Potential?

We investigate the perimeter losses in each sub‐cell of a small area 2‐terminal perovskite‐silicon tandem device with poly‐Si on oxide based bottom cell passivation. We vary the shaded diode areas by patterning them on the solar cell or using different aperture masks during J–V measurement. By numerical device simulations, we reveal a perimeter‐induced open‐circuit voltage reduction from 1912 to 1858 mV for our device geometries of 1 cm 2 aperture area on 6.25 cm 2 ‐sized silicon bottom cells. The largest part of Δ V OC = 26 mV is attributed to recombination in the shaded silicon wafer. A V OC loss of 14 mV is attributed to the shaded poly‐Si diode. The shaded perovskite top cell induces a V OC loss of 14 mV, if the perovskite total area is 1.44 cm 2 as in our current device. Our so far best in‐house measured efficiency is 26.7%. Simulations show, that implementing our improved perovskite top cell and front fingers can increase the efficiency by about 2.6% abs . and omitting the perimeter losses additional 1.2% abs. . The investigation shows that shading losses are significant and thus have to be taken into account when experimentally assessing the efficiency potential of tandem cells on small area devices.