Retarding Phase Segregation via Lattice Reinforcement for Efficient and Stable Perovskite/Organic Tandems

The operational perovskite/organic tandems are subjected to light irradiation and driven by a higher bias voltage than single-junction solar cells, posing a severe challenge to their stabilities. Light irradiation can trigger halide phase segregation in the perovskite subcell, exacerbated under higher bias voltage through electron-phonon coupling. To address this, dimethylammonium ion (DMA⁺) incorporation delays perovskite crystallization by forming an intermediate phase, enhancing crystallinity, and reducing lattice structural defects. DMA⁺ with a larger ionic radius entering the A-site of lattice tilts the [PbX₆]^4- (X: I or Br) octahedral, enlarging the perovskite bandgap, shortening Pb─I bonds, and reinforcing the lattice. This mitigates halide escaping from the lattice and subsequent ion migration. Phase segregation in the perovskite subcell is significantly suppressed under high-power irradiation and bias voltage. Consequently, the perovskite subcell exhibits increased and stable quasi-Fermi-level splitting values, delivering a high open-circuit voltage of 1.34 V. Notably, 0.062-cm² and 1.004-cm² perovskite/organic tandems achieved remarkable efficiencies of 26.15% (certified of 25.34%) and 24.87%, respectively, exhibiting excellent operational stability of T₉₀ ∼ 1350 h.