Sharp exponential band tails in highly disordered lead sulfide quantum dot arrays

Erslev, Peter T.; Chen, Hsiang‐Yu; Gao, Jianbo; Beard, Matthew C.; Frank, Arthur J.; Lagemaat, Jao van de; Johnson, Justin C.; Luther, Joseph M.

doi:10.1103/physrevb.86.155313

Cited by 58 publications

(78 citation statements)

References 49 publications

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“…[66][67][68] A large fraction of the atoms in a NC is at its surface, which is dynamic and crystallographically disordered. [ 34,[69][70][71] This structural disorder leads to disorder in the electronic structure of NCs immediately after synthesis, and Figure 1. Basic characterization of surface passivation.…”

Section: Synthesis Characterization and Stability Of Pbse Ncsmentioning

confidence: 98%

Role of PbSe Structural Stabilization in Photovoltaic Cells

Asil

Walker

Ehrler

et al. 2014

Adv Funct Materials

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Semiconductor nanocrystals are promising materials for printed optoelectronic devices, but their high surface areas are susceptible to forming defects that hinder charge carrier transport. Furthermore, correlation of chalcogenide nanocrystal (NC) material properties with solar cell operation is not straightforward due to the disorder often induced into NC films during processing. Here, an improvement in long‐range ordering of PbSe NCs symmetry that results from halide surface passivation is described, and the effects on chemical, optical, and photovoltaic device properties are investigated. Notably, this passivation method leads to a nanometer‐scale rearrangement of PbSe NCs during ligand exchange, improving the long‐range ordering of nanocrystal symmetry entirely with inorganic surface chemistry. Solar cells constructed with a variety of architectures show varying improvement and suggest that triplet formation and ionization, rather than carrier transport, is the limiting factor in singlet fission solar cells. Compared to existing protocols, our synthesis leads to PbSe nanocrystals with surface‐bound chloride ions, reduced sub‐bandgap absorption and robust materials and devices that retain performance characteristics many hours longer than their unpassivated counterparts.

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Section: Synthesis Characterization and Stability Of Pbse Ncsmentioning

confidence: 98%

Role of PbSe Structural Stabilization in Photovoltaic Cells

Asil

Walker

Ehrler

et al. 2014

Adv Funct Materials

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“…To date, most works have focused on the transport in CQD solids [15][16][17] or the photophysics 18 , and only a few have investigated the working mechanisms of CQD solar cells in detail 14,19,20 . In this letter, we use timedelayed collection field (TDCF) 21 , bias-assisted charge extraction (BACE) 22 and steady state measurements to investigate free charge generation and recombination in PbS CQDs Schottky structure solar cells.…”

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confidence: 99%

Free carrier generation and recombination in PbS quantum dot solar cells

Kurpiers

Balazs

Paulke

et al. 2016

Applied Physics Letters

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Time Delayed Collection Field (TDCF) and Bias Assisted Charge Extraction (BACE) experiments are used to investigate the charge carrier dynamics in PbS colloidal quantum dot solar cells. We find that free charge carrier creation is slightly field dependent, thus providing an upper limit to the fill factor. BACE measurements reveal a rather high effective mobility of 2 × 10 cm²/Vs, meaning that charge extraction is efficient. On the other hand, a rather high steady state non-geminate recombination coefficient of 3 × 10 cm³/s is measured. We, therefore, propose rapid free charge recombination to constitute the main origin for the limited efficiency of PbS colloidal quantum dots cells.Colloidal quantum dots (CQDs) are a promising class of materials for optoelectronic applications due to their well-tunable optical and electronic properties. In the last years improvement in the quality of the CQDs, as a consequence of better and cleaner synthetic processes, has stimulated their use in a variety of applications from light emitting diodes 1 to solar cells 2,3 , field effect transistors 4-6 and photocatalytic devices 7,8 . The size-induced quantum confinement in the quantum dots can be tuned via precise tuning of the QDs dimensions. This quantum confinement can be partially maintained even in strongly coupled CQD solids 9 . Strong coupling is achieved through the ligand exchange process, by which the original, bulky organic ligands are replaced with shorter ones, enhancing the electronic coupling. Lead chalcogenide quantum dot solids exhibit a very broad absorption range, extending into the near infrared region 10 . This makes them particularly attractive for photovoltaic devices with high photocurrents 11 . From the early Schottky devices 9,11 , which show limited open circuit voltage (V oc ) and fill factors (FF), great improvement in the device structure and in the choice of ligands led to a record PbS CQD solar cell with efficiencies up to 10%. That record device showed a short circuit current of up to 22 mA/cm 2 , V oc of 0.63 V and FF of 0.7 12 . Still, the device performance seems to be limited by the V OC and the FF, purportedly due to recombination

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“…In solar cells, these materials have recently exceeded 7% certified power conversion efficiency (PCE) 5,12,13 , offering a promising path towards efficient, low-cost and roll-to-roll processed photovoltaics (PVs). Recent efforts have concentrated on eliminating trap states detrimental to carrier lifetime 5,14,15 , investigating the impact of size polydispersity on an ensemble of CQDs 16,17 , improving charge collection 13,18,19 , characterizing field-effect mobility in these materials [20][21][22][23] and developing novel doping strategies to enable new high-efficiency device architectures 6,[24][25][26] . However, present-day devices still suffer from current densities and fill factors that are well below their theoretical potential.…”

mentioning

confidence: 99%

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

et al. 2014

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Colloidal quantum dots are attractive materials for efficient, low-cost and facile implementation of solution-processed optoelectronic devices. Despite impressive mobilities (1-30 cm 2 V À 1 s À 1 ) reported for new classes of quantum dot solids, it is-surprisingly-the much lower-mobility (10 À 3 -10 À 2 cm 2 V À 1 s À 1 ) solids that have produced the best photovoltaic performance. Here we show that it is not mobility, but instead the average spacing among recombination centres that governs the diffusion length of charges in today's quantum dot solids. In this regime, colloidal quantum dot films do not benefit from further improvements in charge carrier mobility. We develop a device model that accurately predicts the thickness dependence and diffusion length dependence of devices. Direct diffusion length measurements suggest the solid-state ligand exchange procedure as a potential origin of the detrimental recombination centres. We then present a novel avenue for in-solution passivation with tightly bound chlorothiols that retain passivation from solution to film, achieving an 8.5% power conversion efficiency.

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Sharp exponential band tails in highly disordered lead sulfide quantum dot arrays

Cited by 58 publications

References 49 publications

Role of PbSe Structural Stabilization in Photovoltaic Cells

Role of PbSe Structural Stabilization in Photovoltaic Cells

Free carrier generation and recombination in PbS quantum dot solar cells

Engineering colloidal quantum dot solids within and beyond the mobility-invariant regime

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