When photoluminescence, electroluminescence, and open-circuit voltage diverge – light soaking and halide segregation in perovskite solar cells (original) (raw)
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Identifying Fundamental Limitations in Halide Perovskite Solar Cells
by defect levels, interfacial states, energetic disorder, as well as fi rst-order and bimolecular recombination. qV oc for perovskite solar cells is typically in the range of 0.9-1.1 eV at room temperature ( q is the elementary charge). The small difference E g − qV oc ≈ 0.5 eV (at standard test conditions of one-sun irradiance, AM 1.5G spectrum and cell temperature T = 298 K) compares favorably to other photovoltaic technologies, being lower than organic or dye-sensitized cells (≈0.7 eV), quantum-dot cells (≈0.8 eV), polycrystalline CdTe (≈0.6 eV), and only slightly higher than crystalline silicon (≈0.4 eV). The small energy loss implicitly indicates a modest degree of both electronic disorder and recombination losses in halide perovskites, remarkable for a low-temperature solutionprocessed semiconductor.
Solar RRL, 2020
Bringing the Voc of a perovskite solar cell toward its radiative value, corresponding to a 100% external fluorescence quantum yield (QY) of the cell, has been pursued to reach the highest performance photovoltaic devices. At such aim, many works have focused on maximizing the QY of the active layer isolated from the rest of the cell layers. However, such quantity does often not correlate with Voc following the ideal diode relation. Herein, the QYs of complete FA0.8MA0.2PbI3-yBry solar cells are reported, ranging from 0.1 to 3%, and compare them with their Vocs, ranging from 1 to 1.13 V. By combining these measurements with electromagnetic simulations based on a full-wavevector detailed balance and a fluorescence power loss model, it is demonstrated that a non-optimal Voc in mixed-cation lead halide perovskite cells is not only due to non-radiative photocarrier recombination at traps. Besides the expected parasitic absorption of the emitted photons in the electrode layers, discrepancies appear between Voc and QY. These discrepancies are attributed to the rise of energy barriers, a side-effect of trap removal. Indeed, although surface passivation may enhance the QY, its beneficial effect may be counterbalanced by the emergence of such barriers between active and charge transporting layers. Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))
Defects in halide perovskite semiconductors: impact on photo-physics and solar cell performance
Journal of Physics D: Applied Physics, 2020
Imperfections such as heterogeneity at different length scales, static versus dynamic disorders, defects in the bulk, surface imperfections, grain boundaries, and interface imperfections of solution-processed hybrid metal—halide perovskite semiconductors are known to be detrimental to the solar cell performance. These imperfections influence voltage losses and charge transport by the formation of undesirable non-radiative channels. Photo-generated charge carriers recombine via these non-radiative channels and hamper the performance of perovskite solar cells (PSCs). Scientists are aiming to decode the nature of these defects by a better understanding of their origins and by developing novel engineering techniques for the passivation of defect states. In this review article, we explain the different kinds of imperfection and discuss their impact on charge carrier transport in PSCs through optical studies. Furthermore, we summarize the efforts made in the community to passivate these d...
Mixed Halide Perovskite Solar Cells: Progress and Challenges
Critical Reviews in Solid State and Materials Sciences, 2019
Single and mixed-halide perovskite solar cells (PSCs) have attracted a lot of research attention in recent years due to their solution process-ability, lightweight and excellent photoelectric conversion which are the necessary conditions for low-cost thin-film solar cell technology. The power conversion efficiency (PCE) of solid-state PSCs has risen quickly to a certified value as high as 22%. There is still tremendous potential for the realization of highly efficient solution processable perovskite-based solar cell. The perovskite produced by way of mixing halogen elements, such as CH 3 NH 3 PbI 3-x Cl x and CH 3 NH 3 PbI 3-x Br x , offered several benefits such as enhanced device stability, improved carrier transport and reduced carrier recombination. Single crystal perovskite film containing organic and inorganic cation reported to have broad optical absorption which covers significant part of the solar spectrum. It also exhibited good thermal stability compared to single halide such as CH 3 NH 3 PbI 3. The device configuration of PSCs and the choice of suitable hole/electron transport materials played a significant role in the device performances. This review article reports on the recent advances of solution processed PSC with emphasis on the role played by mixed halide elements on the performance of devices.
Mixed halide perovskite light emitting solar cell
Journal of Physics: Conference Series, 2018
We demonstrate that the halide perovskite planar solar cells with the architecture of ITO/PEDOT:PSS/Perovskite/PCBM/LiF/Al show a switchable dual operation of descent photovoltaic and quite bright electroluminescence in visible range. In our experiments, the active layer is made of a mixed halide perovskite (MAPbBr 2 I) and the device is properly cycled upon light and bias exposure. We argue that this curious effect of switchable double functionality between solar cell and light-emitting device in one architecture is caused by photoinduced segregation in the perovskite. It is shown that the bright red electroluminescence at low voltage of ~ 2 (3) eV appears only after cycling the device in PV regime. On the other hand, electroluminescence operation also effects the following PV mode. This effect is caused by redistribution of photoactivated ions I-/Brand their vacancies during photoexcitation in PV regime.
Dipolar cation accumulation at interfaces of perovskite light emitting solar cells
arXiv (Cornell University), 2019
Ionic migration in organo-halide perovskites plays an important role in operation of perovskite based solar cells and light emitting diodes. Despite the ionic migration being a reversible process, it often leads to worsening of perovskite based device performance, hysteresis in current-voltage characteristics, and phase segregation in mixed halide perovskites being as the most harmful effect. The reason is in dynamical band structure changes, which controllable engineering would solve one of the biggest challenges for development of light-emitting solar cells. Here we demonstrate controllable band bending due to migration of both cation and anion ions in mixed halide perovskite devices. The band structure rearrangement is demonstrated in light emitting solar cells based on the perovskite with organic cations methylammonium (MA +) and formamidinium (FA +), possessing non-zero dipole momentum of 2.29 and 0.21 Debye, respectively, and with PEDOT:PSS and C60 transport layers having a high barrier of 0.8 eV for charge injection. Under applied external voltage MA + and FA + cations move towards the electron transport layer and form a dipole layer at the perovskite/electron transport interface, which lowers threshold voltage for electroluminescence down to 1.7 V for MAPbBr2I and 2.6 V for FAPbBr2I, whereas monohalide perovskite MAPbBr3 does not demonstrate such behavior. This ability to in-situ change the device band structure paves the way developing of dual-functional devices based on simple design. It also makes mixed halide perovskites more flexible than mono halides ones for developing different optoelectronic devices without the use of special types of work function modifying transport materials.
Advanced Energy Materials, 2014
postulate stating that a solar cell functions as a light-emitting diode (LED) when charges are injected. This law is a more generalized expression of the equilibrium between absorption and emission, which holds generally and determines the maximum energy-conversion effi ciency of a solar cell. This is known as the Shockley-Queisser limit describing the case of a single band gap semiconductor where recombination of electron-hole pairs is only radiative. The more generalized form based on the quantum effi ciencies allows for an internal quantum effi ciency smaller than unity and includes non-radiative recombination. According to this reciprocity relation, only two quantities of a solar cell have to be measured to predict V oc : the photovoltaic quantum effi ciency spectrum (EQE PV , also called IPCE) and the external quantum effi ciency of the electroluminescence (EQE EL ) at V oc .
Advanced Materials, 2018
Moving away from the high‐performance achievements in organometal halide perovskite (OHP)‐based optoelectronic and photovoltaic devices, intriguing features have been reported in that photocarriers and mobile ionic species within OHPs interact with light, electric fields, or a combination of both, which induces both spatial and temporal changes of optoelectronic properties in OHPs. Since it is revealed that the transport of photocarriers and the migration of ionic species are affected not only by each other but also by the inhomogeneous character, which is a consequence of the route selected to deposit OHPs, understanding the nanostructural evolution during OHP deposition, in terms of the resultant structural defects, electronic traps, and nanoscopic charge behaviors, will be valuable. Investigation of the film‐growth mechanisms and strategies adopted to realize OHP films with less‐defective large grains is of central importance, considering that single‐crystalline OHPs have exhibit...
Effect of Halide Composition on the Photochemical Stability of Perovskite Photovoltaic Materials
ChemSusChem, 2016
The photochemical stability of encapsulated films of mixed halide perovskites with a range of MAPb(I1-x Brx )3 (MA=methylammonium) compositions (solid solutions) was investigated under accelerated stressing using concentrated sunlight. The relevance of accelerated testing to standard operational conditions of solar cells was confirmed by comparison to degradation experiments under outdoor sunlight exposure. We found that MAPbBr3 films exhibited no degradation, while MAPbI3 and mixed halide MAPb(I1-x Brx )3 films decomposed yielding crystallization of inorganic PbI2 accompanied by degradation of the perovskite solar light absorption, with faster absorption degradation in mixed halide films. The crystal coherence length was found to correlate with the stability of the films. We postulate that the introduction of Br into the mixed halide solid solution stressed its structure and induced more structural defects and/or grain boundaries compared to pure halide perovskites, which might be ...
This work is concerned with the modeling of perovskite based hybrid solar cells formed by sandwiching a slab of organic lead halide perovskite (CH 3 NH 3 PbI 3−x Clx) photo-absorber between (n-type) acceptor and (p-type) donor materials-typically titanium dioxide and spiro. A model for the electrical behavior of these cells is formulated based on drift-diffusion equations for the motion of the charge carriers and Poisson's equation for the electric potential. It is closed by (i) internal interface conditions accounting for charge recombination/generation and jumps in charge carrier densities arising from differences in the electron affinity/ionization potential between the materials and (ii) ohmic boundary conditions on the contacts. The model is analyzed by using a combination of asymptotic and numerical techniques. This leads to an approximate-yet highly accurate-expression for the current-voltage relationship as a function of the solar induced photocurrent. In addition, we show that this approximate current-voltage relation can be interpreted as an equivalent circuit model consisting of three diodes, a resistor, and a current source. For sufficiently small biases the device's behavior is diodic and the current is limited by the recombination at the internal interfaces, whereas for sufficiently large biases the device acts like a resistor and the current is dictated by the ohmic dissipation in the acceptor and donor. The results of the model are also compared to experimental current-voltage curves, and good agreement is shown.