Charge carrier mobility dynamics in organic semiconductors and solar cells

Gulbinas, Vidmantas

doi:10.3952/physics.v60i1.4160

Cited by 4 publications

(4 citation statements)

References 117 publications

(160 reference statements)

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“…This is expected because laser carriers in this time domain still reside in the high-energy part of DOS and the population of low-energy states by sun carriers plays a nonessential role in their dynamics. This allows us to conclude that individual charge carriers generated by sun light under real solar cell operation conditions also experience identical fast mobility decay on a ps–ns time scale as reported in previous studies. , …”

Section: Resultssupporting

confidence: 78%

“…This allows us to conclude that individual charge carriers generated by sun light under real solar cell operation conditions also experience identical fast mobility decay on a ps−ns time scale as reported in previous studies. 18,34 The right-hand side of Figure 2 shows carrier extraction dynamics obtained by integrating TPCs shown in the inset. Notably, as the inset shows, the charge extraction at low U Eff = 0.2 V is faster during initial 1−2 μs in the presence of 1 sun light.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…We used this ultrafast optical pump–probe technique to evaluate the carrier mobility kinetics on a ps–ns time scale. It is explained in detail elsewhere. , In short, drifting charge carriers produced by a femtosecond laser pulse screen the electric field, which is probed by recording the intensity of the electric field-induced second harmonic (EFISH) signal created by the probe pulse applied after a variable delay. The EFISH signal depends on the electric field strength quadratically.…”

Section: Methodsmentioning

confidence: 99%

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Carrier Mobility Dynamics under Actual Working Conditions of Organic Solar Cells

et al. 2021

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Although organic photovoltaics has made significant progress since its appearance decades ago, the underlying physics of charge transport in working cells is still under debate. Carrier mobility, determining the carrier extraction and recombination, is one of the most important but complex and still poorly understood parameters. Low-energy charge carrier states acting as traps play a particularly important role in carrier transport. Occupation of these states under real operation conditions of solar cells induces additional complexity. In this study, we use several transient methods and numerical modeling to address carrier transport under actual working conditions of bulk heterojunction organic solar cells based on fullerene and nonfullerene acceptors. We show that occupation of low-energy states strongly depends on the blend materials and the effective electric field. We define conditions when such occupation increases carrier mobility, making it less time-dependent on the microsecond time scale, and when its influence is only marginal. We also show that the initial mobility, determined by carrier relaxation within the high-energy part of the distributed density of states, strongly decreases with time independently of the low-energy state population.

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Section: Resultssupporting

confidence: 78%

Section: ■ Results and Discussionmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Carrier Mobility Dynamics under Actual Working Conditions of Organic Solar Cells

et al. 2021

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“…When techniques with different time scales are combined so that the entire time range of pico-μs is covered, it becomes apparent, as shown in Figure 5, that mobility can have a significant time dependence and ultrafast time-resolved measurements can give higher mobility values than (near) steady-state methods. [88,89,93,99] The time-dependence in mobility was confirmed by kMC simulations, while the simulated steadystate value predicted by simulations agreed well with the value determined by photo-CELIV. [88] A consequence of this is that steadystate techniques such as SCLC or photo-CELIV may significantly underestimate the mobility of photogenerated charges at operating conditions as the thermalization is considered to be slower than the carrier extraction, especially in thin devices with a large disorder 𝜎 DOS .…”

Section: Photocurrentsupporting

confidence: 74%

Equilibrium or Non‐Equilibrium – Implications for the Performance of Organic Solar Cells

Scheunemann

Göhler

Tormann

et al. 2023

Adv Elect Materials

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With power conversion efficiencies approaching 20%, organic solar cells can no longer be considered the ugly duckling of photovoltaics. Successes notwithstanding, there is still a need for further improvement of organic solar cells, both regarding energy and current management in these devices. At present, there are different and mutually exclusive interpretation schemes for the associated losses of energy and charge, hampering the rational design of next generations of organic solar cells. One critical factor that affects voltage, current, and fill factor losses is whether or not photogenerated charges are effectively near or far away from thermodynamic equilibrium. While it is commonly agreed that both the vibronic and (disordered) energetic structure of organic semiconductors affect the solar cell characteristics, the degree to which deviations from near‐equilibrium population of the associated energy level distributions matter for the photovoltaic performance is unclear: near‐equilibrium as well as kinetic descriptions have provided seemingly convincing descriptions of a wide range of experiments. Here, the most important concepts in relation to experimental results are reviewed, open questions are addressed and implications for device performance and improvement are highlighted.

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Ion Motion Determines Multiphase Performance Dynamics of Perovskite LEDs

Chmeliov

Elkhouly

Gegevičius

et al. 2021

Advanced Optical Materials

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them, inherent to all perovskite devices, is the short-term and long-term stability. PeLEDs also suffer from efficiency rolloff limiting their brightness. [7][8][9][10] Another issue, particularly important for the highspeed device operation, is the occurrence of hysteresis [1,11] and variations of the electroluminescence (EL) EQE and photoluminescence (PL) efficiency [3,12] under electrical stress.The performance hysteresis in perovskite solar cells was widely investigated and was attributed to the changes of perovskite-transport layer interfaces or to the motion of mobile ions. [13][14][15][16] Ion motion in metal-halide perovskites is a very complex and still poorly understood phenomenon. Generally, all constituents of metal halide perovskites-halides, lead, and organic cations-may form vacancies, interstitials, and anti-sites, which may be mobile and act as carrier traps. [16][17][18] On the other hand, theoretical evaluations show that only few of them form deep traps acting as non-radiative recombination centers, [17] while shallow traps have a negligible effect on a trap-assisted recombination. [19] In lifetime measurements of PeLEDs, it is constantly observed that different PeLED stacks improve over a timeframe of minutes to hours, then they start to degrade. [3,[20][21][22] Persistent enhancement of the EQE of PeLED, under applied positive voltage (so-called stressing regime), has been explained by the motion of the mobile excess iodide ions that fill vacancies and reduce Perovskite light-emitting diodes (PeLEDs) currently reach up to about 20% external quantum efficiency (EQE) and are becoming a promising technology for display and lighting applications. Still, many issues regarding their performance remain unresolved, particularly those related to stability, operation in non-stationary regimes, and efficiency roll-off at high current densities. Here, some of those issues in PeLEDs based on MAPbI 3 perovskite are addressed. The authors analyze the electroluminescence (EL) and current dynamics after the first-time voltage application and after application of sequences of voltage pulses, at different temperatures. Analysis of the results suggests that the complex dynamics observed on time scales from sub-seconds to minutes and hours can be explained by the spatial redistribution of mobile species, most likely iodine interstitials, characterized by ≈175 meV activation energy. This redistribution alters the carrier injection, spatial electric field, and charge carrier density distributions as well as density of nonradiative recombination centers within the perovskite layer. Mathematical modeling of the ion motion and related processes enabled to reproduce the EL and current dynamics and to disentangle complex sequence of processes governing the PeLED operation.

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Charge carrier mobility dynamics in organic semiconductors and solar cells

Cited by 4 publications

References 117 publications

Carrier Mobility Dynamics under Actual Working Conditions of Organic Solar Cells

Carrier Mobility Dynamics under Actual Working Conditions of Organic Solar Cells

Equilibrium or Non‐Equilibrium – Implications for the Performance of Organic Solar Cells

Ion Motion Determines Multiphase Performance Dynamics of Perovskite LEDs

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