Mechanically tuning spin-orbit coupling effects in organic-inorganic hybrid perovskites

Organic-inorganic hybrid perovskites have potential applications in flexible electronics based on solution-processing polycrystalline thin-films. This article reports an emerging phenomenon: mechanically tunable spin-orbit coupling (SOC) in flexible perovskite solar cells under elastic bending. Polarization-dependent photocurrent studies show that mechanical bending increases the orbit-orbit interaction, shown as an enhanced SOC, and consequently boosting the intersystem crossing to convert optically generated bright states (which are allowed to recombine) into dark states (which are forbidden to recombine) in flexible perovskite solar cells [PET/ITO/PEDOT:PSS/MAPbI(3-x)Cl(x)/PCBM/PEI/Ag]. Simultaneously, the photocurrent is increased from 15.39 mA/cm(2) to 22.0 mA/cm(2) by 43% upon such elastic bending with the curvature radius of 4.2 mm. It is further found that introducing mechanical stress leads to both grain boundary interaction and grain deformation shown as the decreased defects at grain boundaries through thermal admittance spectroscopy and the elastic strain verified by X-ray diffraction measurement. The capacitance-frequency characteristics indicate that applying this mechanical stress causes an increase on the bulk polarization by introducing grain boundary interaction and grain deformation. This provides necessary condition to realize mechanically tunable SOC effects in perovskites via electric-magnetic coupling. Essentially, mechanically tunable SOC effects present new mechanisms to control the optoelectronic properties in flexible perovskite electronic devices.