Halide perovskites are currently of intense interest for solar energy and optoelectronic applications. Remarkable gains in performance have been demonstrated in the past few years. However, most current devices are still limited by non-radiative recombination losses. We focus on uncovering and eliminating these loss processes. Experiments suggest that electrical heterogeneities in both the perovskite active layer, as well as the perovskite/electrode interface affect carrier diffusion and non-radiative recombination processes. Both optical and scanning probe microscopy experiments show how grain boundaries slow lateral carrier transport and how interfaces serve as recombination centers in these systems. Multimodal microscopy experiments reveal the combined role of electrochemistry and ion motion on defect formation. We show that by using chemical passivation of the perovskite surfaces we are able to obtain carrier lifetimes and photoluminescence intensities in solution-processed thin films that rival those in the best single crystals, achieving over 90% PL internal quantum efficiency and quasi-Fermi level splittings that exceed approach the Shockley-Queisser limit under illumination. We further explore the defect chemistry on local ion motion and phase stability of mixed perovskites.