Decoupling radiative and non-radiative losses in lead free perovskite solar cells

ended

Lead (Pb) based perovskite solar cells (PSCs) demonstrate a remarkable power conversion efficiency (PCE of 25.2%). Their toxicity, however, raises environmental concerns and might hinder their commercial deployment. Quest for non-toxic PSCs is still at its infancy: The PCE in Pb-free PSCs is merely around 12%, which is about one third of their radiative limit. An analysis of recent literature on the Pb-free PSCs suggests a high non-radiative recombination in them, as evidenced by their high voltage loss and a low fill factor. These non-radiative recombination losses occur due to defects in the perovskite bulk and at the perovskite/charge extraction layers (CTLs) interfaces. Significant research is being carried out to suppress bulk defects, however, systematic investigations of the photophysical and photochemical properties of perovskite/CTLs interfaces remained relatively ignored. For instance, there is no quantitative data to decouple losses in Pb-free PSCs due to bulk and interfacial defects. There is also little information on the chemical and electronic properties of the interface between Pb-free perovskites and different CTLs. This project aims to systematically investigate energetic alignment, charge transfer rates, recombination, trap density and trap depth etc. at the interfaces between Pb-free perovskites and a range of CTLs (organic, inorganic). Measuring quasi-Fermi level splitting and its correlation with open-circuit voltage will help in quantifying losses due to the different interfaces. Based on the insights gained from these investigations, the interfacial properties will be tuned via doping the CTLs or via surface passivation schemes to improve charge transfer/extraction rate. The experimental findings together with insights gained from device simulations will help us to propose an elaborated picture of the loss mechanisms in Pb-free PSCs and to design device architectures to systematically alleviate device performance.