%0 Thesis
%A Krückemeier, Lisa
%T Quantifying Recombination Losses and Charge Extraction in Halide Perovskite Solar Cells
%V 669
%I RWTH Aachen University
%V Dissertation
%C Jülich
%M FZJ-2025-03112
%@ 978-3-95806-835-3
%B Schriften des Forschungszentrums Jülich Reihe Energie & Umwelt / Energy & Environment
%P vi, 286
%D 2025
%Z Dissertation, RWTH Aachen University, 2025
%X Due to their exceptional properties, halide perovskite materials have emerged as promising candidates for efficient and cost-effective photovoltaics, with some devices approaching the performance of silicon solar cells after a decade of research. Despite their remarkable progress, perovskite solar cells suffer from several loss mechanisms that limit their efficiency. However, the rapid development of perovskite research has outpaced advances in analyzing characterization techniques tailored to the unique properties of this material class. Thus, understanding and quantifying the losses within these devices remains difficult, especially in terms of recombination losses and charge-extraction dynamics. This work aims to bridge this gap by proposing innovative approaches and providing tools for analyzing charge-carrier dynamics, which will help correctly interpret and quantify experimental data for perovskite solar cells. The overarching motivation is to contribute to the advancement of perovskite solar cell technology by gaining a deeper understanding of fundamental processes. Transient photoluminescence (TPL) and transient photovoltage (TPV) are popular techniques for monitoring charge-carrier dynamics and investigating recombination losses in perovskites. However, the low doping density of lead-halide perovskites often places the device in high-level injection during these measurements, leading to non-linear relationships between the recombination rates and carrier densities. This behavior leads to challenges in the use of a scalar charge-carrier lifetime as a figure of merit to quantify recombination. Furthermore, the interpretation of data from complete solar cells or multilayer samples is highly challenging due to the superposition of various effects that modulate the charge-carrier concentration. These effects include bulk and interfacial recombination, charge transfer and extraction, and capacitive charging or discharging. While theoretical work on TPL decays in full solar-cell devices has been published for other photovoltaic technologies, a comprehensive theory dealing with the specific situation in halide-perovskite devices is currently missing. In this work, improved spectroscopic techniques with a high dynamic range of data acquisition are combined with time-dependent, numerical simulations with Sentaurus TCAD to break down the complex behavior of charge-carrier dynamics in perovskite solar cells. The dissertation contributes to the field by proposing new methods and analytical models for data analysis of perovskite solar cells. One major contribution involves a comprehensive analysis of transient photoluminescence and transient photovoltage decays, considering non-linear dependencies of the recombination rate on charge-carrier density. This multi-method quantitative data analysis of transient photoluminescence and transient photovoltage decays goes beyond traditional mono-exponential fitting methods, introducing an approach to derive differential decay times as a function of charge-carrier density and quasi-Fermi level splitting. Time-dependent, numerical drift-diffusion simulations of various sample structures, including perovskite films, multilayer systems, and complete devices, provide visualization and explanation of the injection dependence of the decay time and allow distinguishing between different carrier-density-dependent regimes. Building upon these insights, analytical equations are developed that serve as good approximations to the simulated and experimental decay-time functions. These analytical equations facilitate data analysis and the extraction of key material parameters, like trapassisted Shockley-Read-Hall recombination coefficients, by removing the need to do extensive numerical simulations. The analytical approach is further expanded to include the extraction of charge carriers by the interlayers and contacts, in addition to recombination. A twocomponent model for small-signal measurements is developed that is based on the analytical solution of coupled linear differential equations via the determination of eigenvalues. The model describes the transient behaviour of chemical and electrical potentials and allows us to connect the rise and decay times in small-signal transientphotovoltage experiments to recombination, extraction, and capacitive charging and discharging effects, providing quantitative values for recombination and extractiontime constants as a function of voltage. Another part of this work is the development of a standardized framework for reporting voltage loss in perovskite solar cells, addressing the impact of perovskite composition changes on the limiting open-circuit voltage, and proposing a consistent reference. This approach, approximating the radiative limit, requires only a single measurement of the external quantum efficiency for its calculation, and is therefore fast and easy to apply. The study compares different band gap definitions used in the literature, revealing a substantial impact on the ranking of the voltage losses. The proposal of referencing open-circuit voltages to the radiative limit enables a meta-analysis of previously published perovskite solar cells. In addition, I present inverted, planar MAPI solar cells with open-circuit voltages exceeding 1.26V. The combination of dry lead acetate and lead chloride precursors, along with optimized hole and electron transport layers, suppresses both bulk and surface recombination, which is confirmed by an exceptionally high photoluminescence external quantum efficiency exceeding 5% in complete cells. These solar cells serve as the basis for subsequent investigations of device physics and characterization techniques. These scientific contributions significantly expand the state-of-the-art by offering innovative methodologies for characterizing halide perovskite solar cells. The proposed frameworks and analytical approaches not only fill existing gaps in understanding the implications of unconventional material properties, but also pave the way for more accurate and comprehensive analysis in future perovskite research.
%F PUB:(DE-HGF)3 ; PUB:(DE-HGF)11
%9 BookDissertation / PhD Thesis
%R 10.34734/FZJ-2025-03112
%U https://juser.fz-juelich.de/record/1044223