Low-Dimensional Hetero-Interlayer Enabling Sub-Bandgap Photovoltaic Conversion for Perovskite Solar Cells

Actualizing sub-band gap photovoltaic conversion is effective in remitting energy loss and pushing theoretical efficiency limits for perovskite solar cells (PSCs). Herein, a zero-dimensional organic metal halide based on hydroxyquinoline (HQ) is developed to sensitize PSCs for near-infrared region gain to implement sub-band gap photovoltaic conversion for enhancing power-conversion-efficiency (PCE) of PSCs. [ZnI₄]^2- skeletons containing heavy atoms intensify the direct singlet-to-triplet state transition of organic chromophores HQ. Meanwhile, the triplet energy of HQ is close to resonance with perovskite band gap, favoring the energy transfer to perovskite and exciting the additional electron-hole pairs, which was observed by transient absorption spectroscopy, confirming the sensitization of perovskite to increase sub-band gap photocurrent. HQ₂ZnI₄ modifies electronic and crystal structure, optimizes energy-level arrangement, and acts as a protective layer, realizing considerable PCEs in small (6.25 mm²)-/larger-area (1 cm²) devices and excellent operational stability. This low-cost strategy brings vitality to the light management of PSCs and expands low-dimensional materials.