Transparent electrodes are essential to allow optical transparency for realizing semitransparent perovskite solar cells (ST-PSCs). This study addresses gallium-and titanium-doped indium oxide (IO:GT) between the electron transport layer (ETL) and top electrode to potentially replace conventional indium tin oxide (ITO) used in inverted ST-PSCs. The shallower work function (−4.23 eV) of IO:GT than that (−4.69 eV) of conventional ITO contributes to suppressing the formation of the Schottky barrier and enhancing the charge transport at the ETL/cathode interface. By adopting IO:GT, the ST-PSC exhibits an enhancement in power conversion efficiency (PCE) from 8.59% to 17.90% (certified 17.53%) with an average visible transmittance (AVT) of 21.9%, which is the record PCE at similar AVT among all ST-PSCs reported to date. Moreover, combining these ST-PSCs as the top cell, a four-terminal perovskite-perovskite tandem solar cell is realized, showing a high PCE of 23.35%. Furthermore, the stability of the ST-PSCs is confirmed excellent, maintaining over 96% of the initial PCE after 1864 h (≈77 days) in air ambient without encapsulation, which is better than the device employing a metal cathode. Therefore, these results demonstrate that the adoption of IO:GT can be a promising route for efficient and stable inverted ST-PSCs with preferred transparency.

Inorganic–organic hybrid perovskite solar cells (PSCs) typically embrace Sn-doped In2O3 (ITO) and F-doped SnO2 (FTO) as transparent electrodes, which are rigid and brittle, retarding the commercialization of flexible PSCs (FPSCs). Here, we fabricated flexible amorphous transparent V-doped In–Zn–O (IZVO) thin films with varied concentrations of V atoms at room temperature. The impacts of V concentration on the chemical, electrical, and optical properties of IZVO thin films were thoroughly investigated. The incorporation of V into IZO was demonstrated to suppress the formation of oxygen vacancies and thus reduce the carrier concentration in IZO. The IZVO thin film affords the best electrode performance with an optimum V concentration of 0.46 atom %. In contrast to the conventional ITO transparent electrodes that require a high processing temperature, the amorphous transparent IZVO electrode deposited at a low temperature without any heating and postannealing process showed a low sheet resistance (∼22.6 Ω/□), high conductivity (∼2210 S/cm), high optical transmittance (∼88.8%), and in particular, excellent mechanical flexibility and fatigue robustness. Therefore, the amorphous transparent IZVO electrode-based perovskite solar cells (PSCs) showed superior performance (14.57%) compared to the amorphous ITO electrode-based PSCs (11.96%), due to the significantly improved short-circuit current density (J SC), open-circuit voltage (V OC), and fill factor (FF). Moreover, the IZVO electrode-based FPSC device retained 77% of its initial power conversion efficiency (PCE) after 100 bending cycles, while the PCE of the amorphous ITO electrode-based FPSC dropped by 80% after only 30 bending cycles. Combining the excellent mechanical flexibility and fatigue robustness, the flexible amorphous IZVO electrode shows great potential for highly efficient flexible photovoltaic applications.

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