Remote Trap Passivation in Colloidal Quantum Dot Bulk Nano‐heterojunctions and Its Effect in Solution‐Processed Solar Cells

Rath, Arup K.; Arquer, F. Pelayo Garcı́a de; Stavrinadis, Alexandros; Lasanta, Tania; Bernechea, María; Diedenhofen, Silke L.; Konstantatos, Gerasimos

doi:10.1002/adma.201400297

Cited by 66 publications

(86 citation statements)

References 29 publications

(34 reference statements)

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“…Great efforts have been put in developing surface passivation approaches to reduce the traps, and power conversion efficiency (PCE) of PbS quantum dot photovoltaics (QDPVs) has been significantly improved (over 10%)12131415. Nevertheless, the achieved PCE is still far below the expected and the surface traps remains a key limiting factor for PbS QDPVs161718.…”

mentioning

confidence: 99%

Detecting trap states in planar PbS colloidal quantum dot solar cells

Jin

Wang

Qing

et al. 2016

Sci Rep

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The recently developed planar architecture (ITO/ZnO/PbS-TBAI/PbS-EDT/Au) has greatly improved the power conversion efficiency of colloidal quantum dot photovoltaics (QDPVs). However, the performance is still far below the theoretical expectations and trap states in the PbS-TBAI film are believed to be the major origin, characterization and understanding of the traps are highly demanded to develop strategies for continued performance improvement. Here employing impedance spectroscopy we detect trap states in the planar PbS QDPVs. We determined a trap state of about 0.34 eV below the conduction band with a density of around 3.2 × 10 16 cm −3 eV −1 . Temperature dependent open-circuit voltage analysis, temperature dependent diode property analysis and temperature dependent build-in potential analysis consistently denotes an below-bandgap activation energy of about 1.17-1.20 eV.PbS colloidal quantum dots (PbS QDs) are attractive materials for next generation photovoltaic devices due to their facile solution processing, low material cost, long term air stability and possibility of tailoring their optoelectronic properties by tuning size, composition and surface chemistry 1-4 . However, PbS QDs in solution are typically surrounded by long aliphatic ligands and once they form solid film, the long ligands act as barriers for charge transfer and transport between neighboring QDs 5-7 . The ligand-exchange procedure, which is used to remove such long ligands can create many surface traps such as vacancies and dangling bonds 8,9 , these traps assist carrier recombination, and hence seriously limit the device performance 10,11 . Great efforts have been put in developing surface passivation approaches to reduce the traps, and power conversion efficiency (PCE) of PbS quantum dot photovoltaics (QDPVs) has been significantly improved (over 10%) [12][13][14][15] . Nevertheless, the achieved PCE is still far below the expected and the surface traps remains a key limiting factor for PbS QDPVs [16][17][18] .Trap states in the PbS QDPVs has been carefully investigated to understand how they limit the device performance. Here we employ Impedance Spectroscopy (IS) to obtain the information of the trap states in our fabricated device with currently most advanced architecture of ITO/ZnO/PbS-TBAI/PbS-EDT/Au (shown in Fig. 1(a)) 12,13 . In such a device the diode property is from ZnO/PbS-TBAI heterojunction, and the PbS-EDT layer acts as an electron-blocking layer between the PbS-TBAI layer and the Au anode 24 . For the ZnO/PbS-TBAI heterojunction, after suitable illumination (mainly for the UV region), the ZnO doping density is much higher than the PbS-TBAI doping density, thereby can be regarded as a N + P abrupt junction, with the depletion region locates in the PbS-TBAI film 25,26 . In our study we use AM 1.5 illumination (10 min AM 1.5 illumination) to generate a N + P ZnO/PbS-TBAI heterojunction, and then performed various measurements including current-voltage and capacitance-voltage under various temperatures to gain information in...

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confidence: 99%

Detecting trap states in planar PbS colloidal quantum dot solar cells

Jin

Wang

Qing

et al. 2016

Sci Rep

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“…We suggested that in the mixed layers, the mid‐gap trap states of the p‐type PbS CQDs are partly filled with electrons donated by the nearby n‐type ZnO or Bi 2 S 3 . This model can further explain the increase of the band‐edge PL of the PbS CQDs when the dots are mixed with ZnO nanoparticles . Overall, remote doping of CQDs by other molecules or nanocrystalline materials, such as metallic nanoparticles, is an interesting concept, however, there are certain factors that limit its use in optoelectronic devices.…”

Section: Doping Schemesmentioning

confidence: 92%

“…The researchers reported that the conductance of the composite films was increased by 100 times compared with the conductance of either of the constituent materials, owing to p‐type doping of the PbTe by the Ag 2 Te crystal phase. We proposed similar doping in the context of explaining the superior electrical characteristics of solar cells that employ bulk nanoheterojunction (BNH) layers of PbS CQDs mixed with ZnO or Bi 2 S 3 nanoparticles . We suggested that in the mixed layers, the mid‐gap trap states of the p‐type PbS CQDs are partly filled with electrons donated by the nearby n‐type ZnO or Bi 2 S 3 .…”

Section: Doping Schemesmentioning

confidence: 99%

Strategies for the Controlled Electronic Doping of Colloidal Quantum Dot Solids

Stavrinadis

Konstantatos

2016

ChemPhysChem

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Over the last several years tremendous progress has been made in incorporating colloidal quantum dot (CQD) solids as photoactive components in optoelectronic devices. A large part of this progress is associated with significant advancements made in controlling the electronic doping of CQD solids. Today, a variety of strategies exists towards that purpose; this Minireview aims to survey the major published works in this subject. Additional attention is given to the many challenges associated with the task of doping CQDs, as well as to the realization of optoelectronic functionalities and applications upon successful light and heavy electronic doping of CQD solids.

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“…Since the first reports 1,2 , a dramatic improvement in power conversion efficiency (PCE) has been achieved overpassing 9% with PbS(Se) QDs leading the race as the material of choice 5 . This progress has been underpinned by the design of new heterostructures [5][6][7][8] , improved surface passivation schemes 3,4 and advanced device architectures for more efficient charge collection and suppressed recombination 9,10 . While improvement in PCE of QD solar cells has been thoroughly sought after over the years, the photostability of this technology still remains an open challenge to further increase its technology readiness level, albeit initial promising results on low-performance PbS QD solar cells 11 .…”

Section: Icrea-institució Catalana De Recerca I Estudis Avançats Llumentioning

confidence: 99%

The role of surface passivation for efficient and photostable PbS quantum dot solar cells

et al. 2016

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For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached efficiency about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of quantum dot's surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimised surface passivation and suppression of hydroxyl ligands-which are found to be detrimental for both efficiency and photostability-the efficiency remains within 80% after

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Remote Trap Passivation in Colloidal Quantum Dot Bulk Nano‐heterojunctions and Its Effect in Solution‐Processed Solar Cells

Cited by 66 publications

References 29 publications

Detecting trap states in planar PbS colloidal quantum dot solar cells

Detecting trap states in planar PbS colloidal quantum dot solar cells

Strategies for the Controlled Electronic Doping of Colloidal Quantum Dot Solids

The role of surface passivation for efficient and photostable PbS quantum dot solar cells

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