Efficient and stable perovskite solar cells via organic surfactant interfacial passivation

Nowadays, the photovoltaic (PV) performance of metal halide perovskite solar cells (PVSCs) is limited by defect state induced recombination at charge transport electrode/perovskite interfaces. These defects, most commonly under-coordinated lead and halide ions, have to be eliminated or passivated in order to promote the device efficiency towards its theoretical limit. In this work, a simple and effective passivation method is reported for PVSCs by employing cis-9-octadecenylamine (CODA), a frequently-used organic surfactant. The CODA passivation layer is positioned between the perovskite absorber and hole transport layer (HTL). The passivated layer is deposited by a spin-coating method and modulated by changing the CODA concentration. We find that the amine ligands on the CODA surfactant are likely to conduce to the distinguished passivation via forming coordination bonds with Pb2+ or I- ions, and hydrophobic connecting alkyl chain networks assembled on the top perovskite absorber surface also helps to resist penetration of humidity and hamper ion migration. CODA is able to efficiently reduce the charge trapping densities by passivating and/or decreasing of defects. Eventually, at an optimal CODA concentration, the perovskite absorbers that are amply passivated by CODA make the devices achieve a high open-circuit voltage (VOC) of 1.15 V and a champion efficiency of 20.87%. The resulting unpackaged device displays considerably enhanced ambient stability over 144 h while maintaining over 80% of its original efficiency under the relative humidity of 50% in the ambient air.