Surface functionalization of lead-free Cs3Bi2I9 perovskite films with the ruthenium dye Z907 enables photoinduced charge separation and self-powered photodetection

Surface functionalization with the dye Z907 reconfigures the electronic landscape of lead-free Cs 3 Bi 2 I 9 perovskite photodetectors and triples zero-bias performance. The dye modification layer leaves morphology intact ( R a ≈12 nm) yet passivates traps, as SCLC confirms. Kelvin-probe mapping discloses a 300 mV Fermi-level downshift that aligns the valence band of Cs 3 Bi 2 I 9 with the highest ccupied molecular orbital of P3HT, enabling efficient hole extraction. The Cs 3 Bi 2 I 9 /Z907/P3HT stack delivers a surface photovoltage of 325 mV and cuts rise/decay constants from 496/313–285/286 ms. Transient surface photovoltage traces reveal a polarity reversal, seven-fold surface photovoltage amplification, and a lengthened tail, evidencing redirected carrier flow and suppressed trap-assisted back-transfer. Dynamic intensity-modulated photocurrent spectra display an order-of-magnitude reduction in charge-transfer time and a larger high-frequency phase lead, confirming faster interfacial hole extraction and lower recombination resistance. These dynamics yield a bias-free responsivity and detectivity 2–3 times higher than in bare films, while the device cleanly encodes 8-bit ASCII via binary light pulses, illustrating the promise of molecular interface engineering for energy-autonomous visible-light communication.