| 1. |
- Pazoki, Meysam, et al.
(författare)
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Time resolved photo-induced optical spectroscopy
- 2019. - 1
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Ingår i: Characterization Techniques for Perovskite Solar Cell Materials. - Amsterdam : Elsevier. - 012814727X - 9780128147276 - 9780128147283 ; , s. 139-160
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Bokkapitel (refereegranskat)abstract
- The perovskite layer is the photoactive material within the hybrid perovskite solar cell (HPSC) device by which the incoming photon energies are absorbed and transformed into charge carriers, and after the charge separation, the corresponding charge carriers are transported via the selective contacts for the photovoltaic operation. Optical fingerprints of these physical processes i.e. the spectral response during light absorption, charge separation, transport, recombination as well as other important phenomena such as Stark effects, electron-phonon interactions, ionic movement and Frenkel defect annihilation can be studied within the scope of time resolved photo-induced optical spectroscopy. The time scales of the main fundamental processes within perovskite solar cells directly affect the device performance, and can differ significantly from conventional solar cell technology devices. The processes varies from femtosecond to several seconds and many are strongly dependent on the chemical composition and crystal quality of the material. Full characterization of the physical properties of the device, implies a careful attention to the lifetime and amplitudes of the processes, as well as experimental design for distinguishing the processes by considering the appropriate method and/or variation in the chemical composition of the materials. Here we briefly review the relevant underlying physical processes occurring in the system, their fingerprints and how they can be detected by different spectroscopic tools, together with the methodological scopes and limitations.
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| 2. |
- Rahman, Mohammad Ziaur, et al.
(författare)
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X-ray diffraction and Raman spectroscopy for lead halide perovskites
- 2019. - 1
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Ingår i: Characterization Techniques for Perovskite Solar Cell Materials. - Amsterdam : Elsevier. - 012814727X - 9780128147276 ; , s. 23-47
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Bokkapitel (refereegranskat)abstract
- Lead halide perovskites (LHPs) have recently emerged as promising materials for solar energy conversions. Here, the underlying optoelectronic properties, charge transport abilities, energy level positions for alignment of contact materials, and the stability of LHPs are all dependence on the material composition and structure. Therefore, understanding the structure-to-property relationships is crucial from both a fundamental perspective as well as for constructing efficient and stable devices based on LHPs. XRD is a century old powerful tool to extract the structure of crystalline materials. It provides means to quantify atomic level distances, extraction of symmetries, densities, compositional and temperature dependent phase transitions as well as orientation and size of crystallites in polycrystalline films. Raman spectroscopy is a versatile characterization technique that provides information about the chemical composition and phases in crystalline materials, as well as the local vibration found in amorphous structures, molecular materials, solvents, and gases. With this knowledge, one can extract chemical identities via observed vibrations, bonding interactions, orientations, symmetries, local and lattice vibrations in a crystalline materials. In this contribution, we succinctly discuss the latest progress in understanding the physical properties of LHPs using XRD and Raman Spectroscopy.
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| 3. |
- Unger, Eva L., et al.
(författare)
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Current-voltage analysis : Lessons learned from hysteresis
- 2019
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Ingår i: Characterization Techniques for Perovskite Solar Cell Materials. - 9780128147283 - 9780128147276 ; , s. 81-108
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Bokkapitel (refereegranskat)abstract
- Progress in the power conversion efficiency of solar cells based on metal-halide perovskite semiconductors has been astonishing for the past years. During their development, transient effects have been observed that gave rise to an uncertainty associated with the determination of device performance from current density-voltage (J-V) measurements. This effect becomes visible in a dependence of the J-V curve on scan rate and direction, causing a J-V hysteresis due to the discrepancy between forward and reverse scan.) This hysteresis has caused debates in the research community and triggered efforts to establish reliable measurement protocols. A major difficulty is that the J-V hysteresis as a function of measurement conditions can be quite specific for the device architecture and conditions the device was subjected to prior to the measurement. In this chapter, we describe hysteresis in perovskite solar cells phenomenologically and summarize the current understanding of underlying causes. We emphasize insight that can be gained from the quantitative analysis of the magnitude of hysteresis and time scales of transient phenomena. In this context, we discuss the value and limitation of hysteresis indices as quantitative metrics in the analysis of hysteresis. We summarize how device architecture, contact layers and composition of the metal-halide perovskite absorber layer affect the magnitude of transient phenomena. In the meantime, uncertainties related to the determination of the power-conversion efficiency have been practically solved by tracking the power output. However, gaining insight into the underlying physical causes for hysteresis is crucial. This understanding will illuminate the intrinsic properties of MHP semiconductors and allow the evaluation of their technological potential also regarding long-term stability.
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