Hybrid perovskites continue their progress towards industrialization with scale-up efforts reporting certified efficiencies more than 10%. Addressing toxicity concerns, due to lead, is clearly the last major hurdle that needs to be cleared to establish viable industrialization potential. Lead-free materials development is clearly in its divergent phase with efforts being focused on divalent, trivalent, tetravalent metal cations and also with structures as diverse as layered, lower dimensionality materials, molecular salts, dimers, and double perovskites. Recent studies have indicated promising photovoltaic properties with Pb replacements in the double perovskite families. These materials need further theoretical and experimental investigations to understand issues such as magnetic ordering, spin-orbit coupling, and trap defect states. Lead with its lone pair s-orbitals seems to play an indispensable role and an approach for partial replacement of Pb with Sn and other transition metals appears to be gathering interest. Lessons learned from oxide perovskites especially in the context of double perovskites are encouraging, however, processability has proven to be a significant barrier and new routes for solar cell fabrication are being explored. It has also become evident that similar to superconductors, battery materials, and thermoelectric, the pursuit of high performance perovskites will lead to multiple dopants, substituents, and large degree of structural diversity. The quest for lead replacement will result in perovskite absorbers comprising multiple cations on both the A and M sites, and also multi-halide variants. These possibilities of structure and materials selection presents us with more than 106 perovskite combinations, necessitating a move away from empirical trial-and-error investigations towards a rational design methodology.
Overall, it can be expected that modern first-principles computational tools will continue to find broad use in fundamental studies of known perovskite solar cell materials, as well as being used as a tool for accelerating the discovery of new materials in this context. To increase the chances of progressing towards higher efficiency perovskites, rational design needs to be expanded to also include: (i) bulk properties related to solar-cell performance e.g. dielectric constants, band alignments, and optical properties (ii) prediction of carrier densities and transition levels under different experimental synthesis conditions and (iii) defect physics relating to deep traps that can compromise photovoltaic performance.
The results will be immediately connected to various activities in the chemistry and materials science communities, including ongoing feedback between theory and experiment. The deeper understanding derived from this work on photovoltaic materials, will certainly make a long-term impact on academic, industrial and environmental research perspectives. The relevant and interesting issues that will arise during the progress of the project would provide numerous topics for future research initiatives and collaborations within the interdisciplinary science, which will be beneficial for Swedish research. In time progress, the project will not only be confined in this region, but can spread throughout the world to the various groups interested in energy production. This will definitely help to disseminate the scientific knowledge within and outside Sweden.