Challenges in the design and synthesis of self-assembling molecules as selective contacts in perovskite solar cells

Self-assembling molecules (SAMs), as selective contacts, play an important role in perovskite solar cells (PSCs), determining the performance and stability of these photovoltaic devices. These materials offer many advantages over other traditional materials used as hole-selective contacts, as they can be easily deposited on a large area of metal oxides, can modify the work function of these substrates, and reduce optical and electric losses with low material consumption. However, the most interesting thing about SAMs is that by modifying the chemical structure of the small molecules used, the energy levels, molecular dipoles, and surface properties of this assembled monolayer can be modulated to fine-tune the desired interactions between the substrate and the active layer. Due to the important role of organic chemistry in the field of photovoltaics, in this review, we will cover the current challenges for the design and synthesis of SAMs PSCs. Discussing, the structural features that define a SAM, (ii) disclosing how commercial molecules inspired the synthesis of new SAMs; and (iii) detailing the pros- and cons- of the reported synthetic protocols that have been employed for the synthesis of molecules for SAMs, helping synthetic chemists to develop novel structures and promoting the fast industrialization of PSCs. We summarize the challenges to design and synthesize self-assembled molecules, discussing their synthetic routes and structural features in relationship to the efficiency of perovskite-based solar cells where they are applied as selective contacts.