Interface and structural engineering of perovskite solar cells towards enhanced stability and performance

Perovskite solar cells have had a meteoric rise in the last decade achieving efficiencies that already rival the most established solar cells technologies. They are easily processed and have excellent optoelectronic properties that make them accessible for many photovoltaics and opto-electronics applications. However, the bottleneck of perovskite solar cells is that they lack the stability required to make them commercially viable. In this thesis, I was working on improving the stability targeting different components of the perovskite device structure including the absorber layer and the interface between the perovskite and hole transporting layers. Finally, I explored new hole transport materials that have the potential to be more stable compared to the currently used spiro-OMeTAD.In chapter 2, Layered perovskites represents a significant approach to enhance the stability of perovskite solar cells and their optoelectronic properties. Therefore, Dion-Jacobson hybrid layered perovskite systems based on 1,4-phenylenedimethylammonium (PDMA) and its perfluorinated phenyl analogue (F-PDMA) were investigated to determine their structure at the atomic scale. The stability was examined in humid environments revealing nanoscale segregation of layered perovskite species based on PDMA and F-PDMA components, along with enhanced stabilities of the perfluoroarene system. In chapter 3, it is shown that a diethylammonium iodide (DEAI) treated surface can mitigate non-radiative recombination losses at the interface between perovskite and hole transport layer by forming a mixed phase of layered perovskite on the surface. The devices performance was enhanced with a champion power conversion efficiency (PCE) of 23.3% while also showing improved stability under operational and thermal conditions.In chapter 4, functionalized graphene oxide with alkali cations (Li, Na, K, Rb, and Cs) was used as interlayer between perovskite and hole transporting layer yielding an improved power conversion efficiency of 23.4%. The solar cells demonstrated excellent operational and thermal stability.Finally, in chapter 5, novel hole transport materials (HTMs) were investigated, demonstrating promising photovoltaic performance. A comprehensive examination of their electronic and optoelectronic properties was conducted to identify the primary factors contributing to efficiency losses, which were found to be associated with suboptimal interface passivation and HTM doping rather than intrinsic properties of the HTM materials themselves. This chapter presents an optimization strategy for these new materials, highlighting their potential as replacements for the current state-of-the-art HTMs.