KEYWORDS: Perovskite, Tandem solar cells, Temperature metrology, External quantum efficiency, Solar cells, Data modeling, Silicon, Absorption, Solar energy, Glasses
Perovskite/silicon tandem solar cells promise power conversion efficiencies (PCE) beyond the thermodynamic limit of single-junction devices. This potential has been unveiled via several champion devices, however, their actual outdoor performance is yet to be investigated. Here, we fabricate 25 %-efficient two-terminal (2T) monolithic perovskite/silicon tandem solar cells and test them outdoors to reveal the characteristics of these devices specifically in hot and sunny climates, which are the ideal locations to operate such efficient photovoltaic devices. In this article, we summarize our observation on the perovskite/silicon tandem solar cells under actual operational conditions and discuss the lessons we take from our interpretations.
Solution-processed metal-halide perovskite solar cells (PSCs) have received immense attention in the field of photovoltaic research due to their outstanding power conversion efficiency (PCE), which has surpassed 24% in a relative short time. Understanding carrier losses at metal halide perovskite/charge transport layer interfaces is a pre-requisite to bring the efficiency closer to the Shockley-Queisser limit. Ultrafast transient absorption spectroscopy is a vital tool to study such a processes and specifically interfacial recombination can accessed through these measurements, and further in-sights into losses associated with the open circuit voltage Voc are gained. Transient spectroscopy techniques will be used to unravel the dynamics of processes limiting the photoluminescence quantum efficiency and thus the Voc. Employing both transient photoluminescence and transient absorption techniques, enables differentiation be-tween various recombination processes. Here we study the impact of the different hole transport layers, namely, PDPP-3T, NiO and PTAA hole transport layers and reveal the charge carrier recombination. We report the direct observation of hole extraction and carrier recombination dynamics of mixed-cation lead mixed-halide perovskite layers interfacing with a polymeric hole transport layer: PDPP-3T. The dynamics of the ground state bleach of the polymer, which directly reveals the hole extraction and re-combination at the perovskite/polymer interface. The perovskite hole mobility was found to be 3.08 cm2 V-1 s-1. To gain further insight into the hole extraction dynamics, we vary the thickness of the perovskite film. We observe that the hole extraction time is slower with increasing the perovskite thickness following optical excitation from the perovskite side. Mimicking the device architecture via introducing an electron transport layer to the perovskite/PDPP-3T stack resulted in slower carrier recombination dynamics due to decreased charge carrier recombination in the perovskite.
KEYWORDS: Solar cells, Internal quantum efficiency, Perovskite, Luminescence, Terahertz spectroscopy, Quantum efficiency, Time resolved spectroscopy, Spectroscopy, Diffusion, Probability theory
Internal quantum efficiency (IQE) is a key parameter determining solar cell power conversion efficiency. While reported IQEs of metal-halide perovskite solar cells are often close to one, the contributions of photoluminescence reabsorption (PLr) and surface recombination (SR) to IQE has not been elucidated. In this work, both effects are examined by photoluminescence spectroscopies and time-resolved terahertz spectroscopy (TRTS). Then PLr rate and SR velocity are extracted from TRTS kinetics by diffusion theory. At last a model is proposed to calculate the carrier-collection probability and discuss contributions of PLr and SR on the IQE.
Mixed halide, mixed cation lead perovskite films have been demonstrated to benefit tremendously from the addition of Cs and Rb into the perovskite formulation, resulting in high performance, enhanced reproducibility and stability. However, the root cause of these effects in these complicated systems is not well understood. We address the above challenge by tracking in situ the solidification of perovskite precursors during solution-casting using time-resolved grazing incidence wide-angle X-ray scattering (GIWAXS). In doing so, we can directly link the formation or suppression of different crystalline phases to the presence of Cs and/or Rb. In the absence of these elements, the multi-component perovskite film is inherently unstable, phase segregating into a solvated MAI-rich phase and a FABr-rich phase. Adding even one of the two (Cs or Rb) is shown to alter the solidification quite dramatically, promoting different solidification pathways. Importantly, the addition of both components in the optimal ratio can drastically suppress phase segregation and promotes the spontaneous formation of the desired perovskite phase. This result is also confirmed by elemental mapping of organic cations (FA+, MA+) and halide anions (I-, Br-) via time-of-flight secondary ion mass spectroscopy (ToF-SIMS). Perovskite precursors with an optimal combination of additives (7% Cs, 3% Rb) result in solar cells with 20.1% power conversion efficiency (PCE), outperforming formulation excluding Cs and Rb (PCE=14.6%). We propose that the synergistic effect is due to the collective benefits of Cs and Rb on the formation kinetics of the perovskite phase, and on the halides redistribution throughout the film. Importantly, our study points to new design rules for tuning the crystallization pathway of multi-component hybrid perovskites.
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