I am not an economics student, but I would like to know about this simply but in details. I would like to understand this Noble Prize winning thoery by Abhijit Banerjee , Esther Duflo and Michael Kremer
Unlike many Nobel prizewinners, this year's award was not really given for a central theoretical development. All three of the winners have made important theoretical contributions relevant to development economics and that inspired their future work (for example Banerjee on networks or Kremer on technological change and productivity). However, their major contribution, and what they received the award for, is their major methodological contributions.
In particular, the winners are responsible for designing and enacting a number of large-scale field experiments in development economics. These experiments use theory and domain knowledge to break poverty down into a series of more manageable problems, and then attempt to actually alleviate one of those problems with a policy intervention. These interventions are administered in randomized ways that allow us to see whether they actually work (like incentives to reduce teacher absenteeism, they found) or not (microfinance, they found).
Through these field experiments they have improved the lives of millions of people in at least some small way, and their work has led to huge changes in the way that development economics operates as a whole (for better or worse, I think better). The field today is much more focused on experimental and other causal work than it used to be, using data and empiricism to answer questions about development economics rather than using theory. In many cases this work focuses on finding actually-effective ways to improve policy and conditions in developing countries.
You can see a more thorough description here: https://marginalrevolution.com/marginalrevolution/2019/10/the-nobel-prize-in-economic-science-goes-to-banerjee-duflo-and-kremer.html