Photoconductivity of PbSe Quantum-Dot Solids: Dependence on Ligand Anchor Group and Length

Gao, Yunan; Aerts, Michiel; Sandeep, C. S. Suchand; Talgorn, Elise; Savenije, Tom J.; Kinge, Sachin; Siebbeles, Laurens D. A.; Houtepen, Arjan J.

doi:10.1021/nn3029716

Cited by 115 publications

(159 citation statements)

References 57 publications

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“…If these features can be combined to produce a high mobility-lifetime product, increased transport lengths should permit the construction of thick absorber layers capable of absorbing the available solar light while maintaining the efficient harvesting of the resultant photocarriers. Despite numerous reports of field effect 23,29,30 and terahertz 22,31 mobilities on the order of 1-30 cm 2 V À 1 s À 1 , which should in principle result in much greater efficiencies than seen today 32 , a PV device has yet to be made that benefits from these increased charge carrier mobilities. Instead, the best certified CQD solar cells reported to date employ active layer materials with fieldeffect mobilities of 10 À 3 -10 À 2 cm 2 V À 1 s À 1 (refs 5,33,34).…”

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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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confidence: 99%

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

et al. 2014

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“…Numerous research groups have worked to quantify these limitations, and consistently arrived at a similar conclusion: major further quantitative improvements in electronic transport are required to continue rapid progress for the field. [14,17,18,[31][32][33][34][35][36] Improved electronic transport must include, but also go well beyond, reporting higher carrier mobilities for charges of each type. Only once lifetime, determined by the presence of recombination centers, is also dramatically improved, can the sum of the diffusion length and drift length become comparable to, and ultimately exceed, the absorption length for light of all solar wavelengths of interest.…”

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confidence: 99%

Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways to improvement

et al. 2013

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Colloidal quantum dot photovoltaic devices have improved from initial, sub-1% solar power conversion efficiency to current record performance of over 7%. Rapid advances in materials processing and device physics have driven this impressive performance progress. The highestefficiency approaches rely on a fabrication process that starts with nanocrystals in solution, initially capped with long organic molecules. This solution is deposited and the resultant film is treated using a solution containing a second, shorter capping ligand, leading to a cross-linked, non-redispersible, and dense layer. This procedure is repeated, leading to the widely employed layer-by-layer solid-state ligand exchange. We will review the properties and features of this process, and will also discuss innovative pathways to creating even higher-performing films and photovoltaic devices.The most abundant and cleanest source of energy available on Earth, solar energy, is also the most underutilized. Its peak intensity is 1000 W/m 2 which, averaged over space and time, provides vastly more energy daily than the global population consumes. Solar energy thus offers, in principle, a compelling option to power a sustainable and increasingly electricitycentric future.[1] While a substantial photovoltaic industry is beginning to take shape worldwide, driven by early generation solar technology based on silicon and compound semiconductors such as cadmium telluride, the fact remains that, in order to compete with traditional energy sources, particularly with cheap and plentiful natural gas, solar photovoltaic systems must cost, fully installed, no more than $1 per watt-peak, which translates to a levelized cost of electricity of approximately $0.05/kWh over a system lifetime.[2] This is noticeably less than current first-and second-generation commercially available solar products, which are held back by higher materials and manufacturing costs; combined with installation costs influenced by the bulky, heavy, and rigid nature of the solar panels themselves.Third-generation photovoltaic systems, including organic, dye-sensitized, and colloidal quantum dot (CQD) solar cells, offer a path to low-weight, low-cost, and prospectively highefficiency solar energy capture and conversion. While thirdgeneration technologies currently function at lower efficiency than commercial first-generation modules, significant pathways exist to reach and surpass the conversion efficiencies required to be commercially feasible.CQD solar cells are of particular interest among the mentioned technologies due to the size tunability of these nanometer-scale semiconductor particles, pictured in Fig. 1(a). The optimal bandgap for a single-junction solar cell as reported by Shockley and Queisser [4] is 1.1 eV; while this offers a limited selection of bulk semiconductors, the quantum confinement effect allows the fabrication of quantum dots (QDs) with reasonable properties [5] using bulk small bandgap semiconductor compounds such as lead sulfide (PbS) and lead selenide (PbSe)...

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“…PVs made using these films, however, do not show clear MEG enhancement to the photocurrent. Instead, supplementing these shorter ligands with longer, thiol-based surface molecules such as mercaptopropionic acid [90] or a mixture of EDT and hydrazine [100,101] shows a clear contribution of MEG, but reduces carrier mobility and overall device efficiency [26][27][28].…”

Section: Surface Passivation Via Ligand Moleculesmentioning

confidence: 99%

Multiple exciton generation in quantum dot-based solar cells

et al. 2017

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Multiple exciton generation (MEG) in quantumconfined semiconductors is the process by which multiple bound charge-carrier pairs are generated after absorption of a single high-energy photon. Such charge-carrier multiplication effects have been highlighted as particularly beneficial for solar cells where they have the potential to increase the photocurrent significantly. Indeed, recent research efforts have proved that more than one chargecarrier pair per incident solar photon can be extracted in photovoltaic devices incorporating quantum-confined semiconductors. While these proof-of-concept applications underline the potential of MEG in solar cells, the impact of the carrier multiplication effect on the device performance remains rather low. This review covers recent advancements in the understanding and application of MEG as a photocurrent-enhancing mechanism in quantum dot-based photovoltaics.

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Photoconductivity of PbSe Quantum-Dot Solids: Dependence on Ligand Anchor Group and Length

Cited by 115 publications

References 57 publications

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

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

Materials processing strategies for colloidal quantum dot solar cells: advances, present-day limitations, and pathways to improvement

Multiple exciton generation in quantum dot-based solar cells

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