Philippe Holzhey1,2
University of Oxford1,Adolphe-Merkel Institute2
Philippe Holzhey1,2
University of Oxford1,Adolphe-Merkel Institute2
Achieving long-term stability of perovskite solar cells is arguably the most important challenge required to enable widespread commercialization. Understanding the perovskite crystallization process and its direct impact on device stability is critical to overcoming this hurdle. Surprisingly, we find that intermediate phases that occur during the crystallization process are critical for long-term stability. The commonly employed Dimethylformamide/ Dimethyl sulfoxide (DMF/DMSO) solvent system for FA<sub>y</sub>Cs<sub>1-y</sub>Pb(I<sub>x</sub>Br<sub>1-x</sub>)<sub>3</sub> perovskite (FACs) results in poor crystal quality, microstructure and the retention of DMSO. That ultimately leads to inferior material stability compared to the here presented DMF/Dimethylammonium (DMF/DMA) processing method. We replace DMSO with DMACl to accurately control the perovskite intermediate precursor phases. By precisely controlling the 2H to 3C perovskite phase crystallization sequence, we tune the grain size, texturing, orientation (corner-up vs face-up) and crystallinity of the FACs perovskite system.<br/><br/>A population of encapsulated devices showed a T80 lifetime, for the stabilized PCE, of 1190 h as median value and a champion device showing a T80 of 1410 h, under simulated sunlight at 65 °C in air, under open-circuit conditions, in contrast to a median value of T80 = 780 hours and a champion T80 = 1040 hours for conventional DMF/DMSO devices. If used in large bandgap perovskites (around 1.8 eV) our devices reach up to 16% stabilised with voltages of up to 1.29 V. An enhancement of 2% and 90 mV compared to the control. Our work introduces an innovative processing route that allows higher overall perovskite device stability with fewer defects, by controlling the intermediate phase domains during the perovskite formation. This work highlights the importance of material quality in order to achieve long-term operational stability, high voltages and shows that it is necessary to find alternative processing routes without DMSO.