Periodic Reporting for period 1 - PROPHET (oPtoelectROnic Properties of Hybrid pErovskiTes)
Okres sprawozdawczy: 2020-01-10 do 2022-01-09
Today, the economic and industrial growth in both developed and emerging countries is progressing at an unprecedented pace. Electricity generation causes a large fraction of greenhouse gases emission worldwide, so realistic alternatives to fossil fuels need to be sought by the scientific community. In this complex scenario, converting solar energy into electricity represents a much-needed solution to meet climate targets and move towards a low-carbon economy. Besides conventional single junction and multi-junction semiconductor photovoltaic devices, new solar cell technologies have evolved from the early 1990s1. However, research into hybrid organic-inorganic metal-halide perovskite solar cells (PSCs) has flourished only over recent years, attracting strong interest by the scientific community. Indeed, this emerging class of devices has become increasingly popular due to the opportunity of reaching a high power conversion efficiency, while being compatible with wet chemistry processing for large area devices. The excellent photovoltaic performance of halide perovskites goes along with a high photoluminescence yield that makes them suitable for a wide range of photonic devices and various optoelectronic applications, such as photodetectors, lasers and light emitting diodes. Moreover, wide band gap PSCs are serious candidate to be the top cell of tandem devices that uses the mature silicon technology as the bottom cell. The tremendous recent progress in PSCs originated from rapid advances in precursor formulation, fabrication methods and device architecture - however, most of the progress has been obtained through empirical device improvements, and several key questions still remain unanswered. Open issues include the optimal chemical composition of the perovskite films, ion migration, scalable fabrication routes, device architecture and stability in operation. PSCs were proven to degrade on a timescale varying from hours to weeks, depending on a number of potential degradation factors, both intrinsic (e.g. stoichiometry, interfaces) and extrinsic (e.g. light, humidity or temperature). The goal of PROPHET is to directly relate the photovoltaic behaviour of PSCs to their optical, electrical, chemical and morphological properties by investigating their photophysics on a range of different length and time scales. Specifically, the action aimed to determine the correlation between physical and chemical properties of hybrid perovskite thin films and their influence on the photovoltaic performance of full devices as well as understand through ex-situ and in-situ characterisation the main degradation processes affecting perovskite thin films and solar cells.
From a scientific point of view, PROPHET allowed me to obtain relevant results related to the objectives of the action. First, potential characterisation-induced artefacts were carefully assessed as hybrid halide perovskites are prone to degradation when exposed to a high-intensity or prolonged electron beam. These tools are commonly used to investigate the chemical or optical properties of materials. Second, the main phenomena governing interfacial recombination and affecting device performance were investigated by coupling continuous wave and transient luminescence imaging techniques. In particular, I focused on studying the role played by the incorporation of PEAI based cations in high efficient inverted perovskite solar cells and in exploring the optoelectronic properties of FAPbI3 thin films deposited by flash IR annealing, a promising technique for perovskite industrialisation leading to devices with increased stability. Third, I studied different degradation process of triple cation perovskites exposed to different kind of external stresses such as light or humidity, identifying the main degradation processes and tracking the evolution of the optoelectronic properties as well as the surface and bulk chemistry.
The development of novel photovoltaic technologies is crucial for a global paradigm change in sustainable power sources. An essential factor contributing to this success is the investigation of halide perovskite solar cells (PSCs) using a wide range of characterization techniques across multiple length scales, with a goal of relating devices remarkable macroscopic optoelectronic properties to their local optical properties and chemical composition. The scientific progress of PROPHET beyond the state of the art concerns the development and the validation of new procedures to investigate beam-sensitive or fragile materials as well as to map their optoelectronic and transport properties. Indeed, the potential characterization induced artifacts has been carefully assessed to ensure the reliability of the analysis. These methods were then employed to investigate the correlation between chemical and physical properties of innovative perovskite materials and passivation strategies and their influence on the photovoltaic performance.