Metal halide perovskites have shown a tremendous progress over the last decade with single junction efficiencies now showing parity with the incumbent silicon technologies for laboratory scale devices. Recent efforts have focused on the translation of these performances to large areas. However, to be competitive with silicon photovoltaics, there is a need for improvement in device stability. As a result, the modification of the top surface of the perovskite absorber and the metal electrode is being investigated in detail. Other than the above, the buried interface of a perovskite solar cell can influence the device stability, by driving chemical reactions at the interface and influencing the compositional homogeneity of the perovskite bulk.

This thesis focuses on developing an understanding at a fundamental level, the influence of the buried interface on performance losses in inverted perovskite solar cells (PSCs), and to devise strategies to realise high efficiencies and improved stability via interface engineering. Firstly, the origin of performance loss in inverted PSCs based on poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as the hole transport material is investigated. This is carried out through careful analysis of the chemical interactions between the constituents in the perovskite precursor and PEDOT:PSS as well through compositional evaluation of the buried PEDOT:PSS layer. Based on the understanding developed, a lead-tin PSC with improved power conversion efficiency of 23.2% and ~66% improved device lifetime is realised through additive engineering. Following this, the wettability challenge of perovskite precursors on the hydrophobic self-assembled monolayer [4-(3,6-Dimethyl-9H-carbazol-9-yl)butyl]phosphonic Acid (Me-4PACz) is evaluated. Alumina nanoparticle-based modification of Me-4PACz is identified as a solution that not only improves the perovskite wettability and thereby device reproducibility, but also results in enhanced carrier lifetimes and high device efficiencies. The influence of the alumina nanoparticles on device stability is investigated where significant improvements in device lifetimes are observed when degraded under ambient conditions at 65 °C in the dark. The origins underlying the improved device lifetime are identified as the efficient scavenging of iodine, improved bulk electrical and surface electronic homogeneity due to the underlying alumina nanoparticle layer.

This thesis highlights the importance of the buried interface in realising high efficiency PSCs through additive engineering to the perovskite bulk and nanoengineering of the buried interface. The design guidelines introduced are applicable not only to single junction devices, but also to multijunction architectures.