High Mobility In2O3:H Electrodes for Four-Terminal Perovskite/CuInSe2 Tandem Solar Cells.

Four-terminal (4-T) tandem solar cells (e.g., perovskite/CuInSe2 (CIS)) rely on three transparent conduc-tive oxide (TCO) electrodes with high mobility and low free carrier absorption in near-infrared (NIR) re-gion. In this work, a reproducible In2O3:H (IO:H) film deposition process is developed by independently controlling H2 and O2 gas flows during magnetron sputtering, yielding high mobility value up to 129 cm2 V-1 s-1 in highly-crystallized IO:H films annealed at 230 ‎°C. Optimization of H2 and O2 partial pressures further decreases the crystallization temperature to 130 ‎°C. By using a highly-crystallized IO:H film as the front electrode in NIR-transparent perovskite solar cell (PSC), a 17.3% steady-state power conversion efficiency (PCE) and an 82% average transmittance between 820 and 1300 nm are achieved. In combina-tion with an 18.1% CIS solar cell, a 24.6% perovskite/CIS tandem device in 4-T configuration is demon-strated. Optical analysis suggests that an amorphous IO:H film (without post-annealing) and a partially-crystallized IO:H film (post-annealed at 150 ‎°C), when used as a rear electrode in NIR-transparent PSC and a front electrode in CIS solar cell, respectively, can outperform the widely used indium-doped zinc oxide (IZO) electrodes, leading to 1.38 mA/cm2 short-circuit current (Jsc) gain in the bottom CIS cell of 4-T tandems.