摘要： Hybrid organic-inorganic perovskites exhibit extraordinary photovoltaic performance. This is believed to arise from almost liquid-like low-energy interactions among lattice ions and charge carriers. While spatial variations have recently been identified over multiple length scales in the optoelectronic responses, the relationship of the heterogeneity and the soft cation-lattice interactions has remained elusive. Here, we apply multivariate infrared vibrational nano-imaging to a formamidinium (FA)-methylammonium (MA)-cesium triple cation perovskite. By using the FA vibrational resonance as a probe of its local chemical environment, through spatial variation and correlation in composition, strength of cation-lattice coupling and its associated few-ps vibrational dynamics, we reveal how a varying local reaction field is correlated with the cation-lattice coupling. We attribute the associated heterogeneous lattice contraction to a non-uniform distribution of cesium cations. The observed varying elasticity of the lattice leads to disordered charge-phonon coupling and polaron formation, the control of which is central to improving perovskite photovoltaics.