Additives are commonly used to increase the performance of metal-halide perovskite solar cells, but detailed information on the origin of the beneficial outcome is often lacking. Herein, the effect of glycine hydrochloride is investigated when used as an additive during solution processing of narrow-bandgap mixed Pb–Sn perovskites. By combining the characterization of the photovoltaic performance and stability under illumination, with determining the quasi-Fermi level splitting, time-resolved microwave conductivity (TRMC), and morphological and elemental analysis a comprehensive insight is obtained. Glycine hydrochloride is able to retard the oxidation of Sn2+ in the precursor solution, and at low concentrations (1–2 mol%) it improves the grain size distribution and crystallization of the perovskite, causing a smoother and more compact layer, reducing non-radiative recombination, and enhancing the lifetime of photogenerated charges. These improve the photovoltaic performance and have a positive effect on stability. By determining the quasi-Fermi level splitting on perovskite layers without and with charge transport layers it is found that glycine hydrochloride primarily improves the bulk of the perovskite layer and does not contribute significantly to passivation of the interfaces of the perovskite with either the hole or electron transport layer (ETL).

Solar-assisted water electrolysis is a promising technology for storing the energy of incident solar irradiation into hydrogen as a fuel. Here, an integrated continuous flow electrochemical reactor coupled to a monolithic perovskite-silicon tandem solar cell is demonstrated that provides light-driven electrochemical solar-to-hydrogen conversion with an energy conversion efficiency exceeding 21% at 1-Sun equivalent light intensity and stable operation during three simulated day-night cycles.