Solution-processed perovskite-colloidal quantum dot tandem solar cells for photon collection beyond 1000 nm

Multi-junction solar cells based on solution-processed metal halide perovskites offer a route to increased power conversion efficiency (PCE); however, the limited options for infrared (IR)-absorbing back cells have constrained progress. Colloidal quantum dot (CQD)-based solar cells, which are solution-processed and have bandgaps tunable to wavelengths beyond 1000 nm, are attractive candidates for this role. Here we report a solution-processed four-terminal (4T) tandem solar cell comprised of a perovskite front cell and a CQD back cell. The 4T tandem provides a PCE exceeding 20%, the highest PCE reported to date for a perovskite-CQD tandem solar cell. The front semi-transparent perovskite solar cell employs a dielectric-metal-dielectric (DMD) electrode constructed from a metal film (silver/gold) sandwiched between dielectric (MoO₃) layers. The highest-performing front semi-transparent perovskite solar cells exhibit a PCE of ∼18%. By tuning the wavelength-dependent transmittance of the DMD layer based on the zero-reflection condition of optical admittance, we build semi-transparent perovskite solar cells with a 25% increase in IR transmittance compared to baseline devices. The back cell is fabricated based on an IR CQD absorber layer complementary to the IR transmittance of the semi-transparent perovskite front cell. Solution-processed hybrid tandem photovoltaics (PV) combining these technologies offer to contribute to higher-efficiency solar cells for next-generation flexible photovoltaic (PV) devices.