Highly efficient air-stable colloidal quantum dot solar cells by improved surface trap passivation

Azmi, Randi,Sinaga, Septy,Aqoma, Havid,Seo, Gabsoek,Ahn, Tae Kyu,Park, Minsuk,Ju, Sang-Yong,Lee, Jin-Won,Kim, Tae-Wook,Oh, Seung-Hwan,Jang, Sung-Yeon unknown 2017 Nano energy Vol.39 No.-

<P><B>Abstract</B></P> <P>While the power conversion efficiency (PCE) of colloidal quantum dot (CQD) solar cells can reach > 10%, the major obstacle for charge extraction and energy loss in such devices is the presence of surface trap sites within CQDs. In this work, highly trap-passivated PbS CQDs were developed using a novel iodide based ligand, 1-propyl-2,3-dimethylimidazolium iodide (PDMII). We examined the effects of PDMII on the surface quality of PbS-CQDs and compared them with TBAI, which is the best-selling iodide based ligand. By using PDMII, improved surface passivation with reduced sub-bandgap trap-states compared to TBAI was achieved. The reduced trap density resulted in enhanced charge extraction with diminished energy loss (0.447eV) in the devices. Solar cell devices using our PDMII based CQDs displayed high PCE and air stability. The certified PCE of our PDMII based devices reached 10.89% and was maintained at 90% after 210 days of air storage.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High efficiency colloidal quantum solar cells (10.99%) using iodide-exchanged quantum dots. </LI> <LI> Efficient reduction of surface trap-states of quantum dots using novel iodide source, PDMII. </LI> <LI> Unprecedentedly high air stability of devices due to improved surface passivation. </LI> <LI> Exceptionally low energy loss in devices using PDMII-exchanged quantum dots. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Highly passivated PbS CQDs were developed using a novel iodide based ligand, 1-propyl-2,3-dimethylimidazolium iodide (PDMII). The effects of PDMII on the surface quality of PbS-CQDs were investigated. By using PDMII, improved surface passivation with reduced sub-bandgap trap-states was achieved. Solar cell devices using our PDMII based CQDs displayed state-of-the-art PCE (10.99%) and air stability with low energy loss (0.447eV).</P> <P>[DISPLAY OMISSION]</P>

Facet-Specific Passivation of Colloidal Quantum Dots Enables Improved Infrared Solar Cells

김영훈 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

Narrow-bandgap PbS colloidal quantum dots (CQDs) provide the attractive opportunity of utilizing the unharvested infrared (IR) solar energy that is transmitted through silicon photovoltaic cells. We demonstrate a novel strategy for facet-specific passivation on (100) and (111) facets of narrow-bandgap CQDs via solution-phase ligand exchange, enabling the highly-passivated and colloidally-stable CQD inks. Our new strategy results in the significantly decreased CQD aggregations as well as the improved photophysical properties. As a result, the resultant CQD solids exhibit the highly enhanced solar cell performance under full solar spectrum and beyond 1100 nm. Considering the surface structure of various colloidal nanocrystals is different and complicated according to the crystal size determined during the synthesis, we believe that our approach opens up a versatile and facile way of achieving further improvements in nanocrystal-based optoelectronic devices.

Colloidal quantum dots for thermal infrared sensing and imaging

Dong-Kyun Ko,Ayaskanta Sahu,Michael Scimeca,Shihab Bin Hafiz 나노기술연구협의회 2019 Nano Convergence Vol.6 No.7

Colloidal quantum dots provide a powerful materials platform to engineer optoelectronics devices, opening up new opportunities in the thermal infrared spectral regions where no other solution-processed material options exist. This mini-review collates recent research reports that push the technological envelope of colloidal quantum dot-based photodetectors toward mid- and long-wavelength infrared. We survey the synthesis and characterization of various thermal infrared colloidal quantum dots reported to date, discuss the basic theory of device operation, review the fabrication and measurement of photodetectors, and conclude with the future prospect of this emerging technology.

Synthesis of colloidal PbS/CuS quantum dots for high performance quantum dots-sensitized solar cells

이형준,권오훈,허진혁,김상욱,임상혁 한국공업화학회 2021 한국공업화학회 연구논문 초록집 Vol.2021 No.1

PbS/ZnO Heterojunction Colloidal Quantum Dot Photovoltaic Devices by a Room Temperature Air-Spray Method

Dasom Park,Aqoma, Havid,Ilhwan Ryu,Sanggyu Yim,Sung-Yeon Jang IEEE 2016 IEEE journal of selected topics in quantum electro Vol.22 No.1

<P>Colloidal quantum-dot-based photovoltaic devices (CQDPVs) were fabricated at room temperature in air atmosphere via a spraying technique. Lead sulfide colloidal quantum dots (CQDs) were utilized for this process and various fabrication conditions such as the spraying pressure, types of ligand molecules, duration of ligand exchange, and the band-gap of the CQDs were investigated in order to optimize the device performance. The power conversion efficiency reached 4.00% (V-OC of 0.57V, J(SC) of 11.79 mA center dot cm(-2), and FF of 0.60) when similar to 145 nm thick sprayed CQD layers were utilized; this value is comparable to that achieved with the conventional spin-coated devices. The generality of the conditions used for fabrication of the sprayed CQDPVs was demonstrated in the fabrication of various CQDs having different band-gaps (1.34-1.61 eV). This technique provides an avenue for the application of a high-throughput process for CQDPV fabrication. Because the materials used herein for device fabrication are not completely optimized, there is further scope for improving device performance.</P>

Stable colloidal quantum dot-based infrared photodiode: multiple passivation strategy

정병규,김우식,오승주 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.5

PbS colloidal quantum dots (QDs) are promising infrared detecting materials because of their widely tunable bandgap spanning the visible to the mid-infrared region, low exciton binding energy, and high electron and hole mobility. PbS QD photodiodes (PDs) exhibit high specifi c detectivity and high energy convergence effi ciency. However, the performance of PbS QDPDs has been limited by the poor degree of ligand passivation on PbS QDs, resulting in oxidation and aggregation of the QDs. Herein, we review the surface morphology of PbS QDs and advanced methods for surface passivation of large PbS QDs. The various methods highlighted in this article provide scientifi c insight for promoting the commercialization of PbS QDPDs in the near future.

Numerical comparison of quantum-confined Stark effect on emission spectra between InP- and CdSe-based colloidal quantum dots

Jang Deokho,Kim Jungho 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.83 No.10

We numerically compare the quantum-confned Stark efect (QCSE) on emission spectra between InP/ZnSe/ZnS and CdSe/ ZnSe/ZnS colloidal quantum dots (QDs). Because the bandgap energy of InP is greater than that of CdSe, the total layer thickness of an InP/ZnSe/ZnS QD is determined to be less than that of a CdSe/ZnSe/ZnS QD for both QDs to have the same emission peak wavelength of 563 nm. After strain-modifed band-edge energies for electron and heavy hole are calculated, a three-dimensional Schrödinger equation is numerically solved based on the fnite element method. The changes in groundstate energy levels, wave-function overlap integrals, and exciton binding energies of the thick CdSe-based QD are much greater than those of the thin InP-based QD when the external electric feld intensity increases from 0 to 100 kV/cm. In calculated emission spectra, the CdSe-based QD shows the integrated emission intensity reduction of 6% and ground-state emission peak shift of 0.91 nm. In contrast, the integrated emission intensity decreases by 0.02% and its ground-state emission peak shifts by 0.06 nm for the InP-based QD. Because the degree of the QCSE is proportional to the size of QDs, the emission spectrum of thin InP-based QDs is less sensitive to the QCSE than that of thick CdSe-based QDs when they have the similar peak emission wavelength.

Origins of the Stokes Shift in PbS Quantum Dots: Impact of Polydispersity, Ligands, and Defects

Liu, Yun,Kim, Donghun,Morris, Owen P.,Zhitomirsky, David,Grossman, Jeffrey C. American Chemical Society 2018 ACS NANO Vol.12 No.3

<P>Understanding the origins of the excessive Stokes shift in the lead chalcogenides family of colloidal quantum dots (CQDs) is of great importance at both the fundamental and applied levels; however, our current understanding is far from satisfactory. Here, utilizing a combination of <I>ab initio</I> computations and UV-vis and photoluminescence measurements, we investigated the contributions to the Stokes shift from polydispersity, ligands, and defects in PbS CQDs. The key results are as follows: (1) The size and energetic disorder of a polydisperse CQD film increase the Stokes shift by 20 to 50 meV compared to that of an isolated CQD; (2) Franck-Condon (FC) shifts increase as the electronegativities of the ligands increase, but the variations are small (<15 meV). (3) Unlike the aforementioned two minor factors, the presence of certain intrinsic defects such as V<SUB>Cl</SUB><SUP>+</SUP> (in Cl-passivated CQDs) can cause substantial electron density localization of the band edge states and consequent large FC shifts (100s of meV). This effect arising from defects can explain the excessive Stokes shifts in PbS CQDs and improve our understanding of the optical properties of PbS CQDs.</P> [FIG OMISSION]</BR>

정공수송층의 재료에 대한 QD-LEDs의 전기 및 광학적 특성 연구

하미영,김강희,문대규 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

나노결정 양자점 및 이를 활용한 디스플레이는 높은 발광효율, 우수한 색재현성 및 색순도, 소자의 안정성 및 용액공정에 대한 용이성 등을 강점으로 가진다. 본 연구에서는 이와 같이 우수한 특성의 QD(Quantum-Dot)를 발광층으로 사용하고, 용액공정 및 열증착 공정을 이용하여 하이브리드 형태의 고효율 양자점 발광 소자(QD-LEDs)를 제작하였다. 특히, 최적의 QD-LEDs의 소자 제작을 위하여 정공수송층의 재료로 정공 이동도가 우수하고, 용액 공정 시, 적층에 용이한 재료인 Poly-TPD [Poly(N,N’-bis(4- butylphenyl)-N,N’-bis(phenyl)-benzidine] 및 PVK (Poly(N-vinyl carbazole)를 이용하였으며, 각 재료별 두께의 변화에 따라서 QD-LEDs의 전기적, 광학적 특성을 분석하였다. 우리는 Poly-TPD를 정공수송층으로 활용한 녹색 QD-LEDs에서 두께가 250 nm일 때, 14.8cd/A (@ 0.102 mA/cm²)의 최대 전류효율을 얻었다. 또한, PVK의 경우는 두께가 100 nm일 때, 11.8cd/A (@ 0.001 mA/cm²)의 전류효율을 가졌다. 이와 같은 결과로 두 재료의 전자 및 정공의 밸런스가 서로 다른 특징을 가지는 것을 알 수 있고, 이것은 두 물질의 정공이동도에 기인한 것으로 사료된다.

메조포러스 이산화티타늄 박막 기반 양자점-감응 태양전지

이효중,Lee, Hyo Joong 한국전기화학회 2015 한국전기화학회지 Vol.18 No.1

본 총설은 다공성의 메조포러스 이산화티타늄 박막을 기반으로 하는 양자점-감응 태양 전지의 최근 발전 과정에 대해 정리하였다. 나노스케일의 무기물 양자점이 가지는 본질적 특성에 기반하고 다양한 양자점 구성 물질을 이용하여, 용액-공정 기반의 다양한 3세대 박막 태양전지를 만들 수 있었다. 양자점 감응제는 준비하는 방법에 따라 크게 2가지로 나눌 수 있는데, 첫 번째는 콜로이드 형태로 용액상에서 준비한 다음 $TiO_2$ 표면에 붙이는 것이고 두 번째는 양자점 전구체가 녹아있는 화학조를 이용하여 직접 $TiO_2$ 표면에 성장시키는 것이다. 폴리썰파이드 전해질을 사용하여, 콜로이드 양자점 감응제의 경우는 최근 들어 정밀한 조성 조절을 통하여 전체 광전 변환효율이 ~7%에 이르렀고 화학조 침전법을 이용하여 준비된 대표적 감응제인 CdS/CdSe는 ~5%의 효율을 보이고 있다. 앞으로는 지금까지 보고된 양자점 감응제의 뛰어난 광전류 생성 능력을 유지하면서, 새로운 정공 전달체의 개발 및 계면 조절을 통한 개방 전압과 채움 상수의 개선을 통한 효율 증가 및 안정성에 관한 체계적 연구가 필요한 상황이다. This review article summarizes the recent progress of quantum dot (QD)-sensitized solar cells based on mesoporous $TiO_2$ thin films. From the intrinsic characteristics of nanoscale inorganic QDs with various compositions, it was possible to construct a variety of 3rd-generation thin film solar cells by solution process. Depending on preparation methods, colloidal QD sensitizers are pre-prepared for later deposition onto the surface of $TiO_2$ or in-situ deposition of QDs from chemical bath is done for direct growth of QD sensitizers over substrates. Recently, colloidal QD sensitizers have shown an overall power conversion efficiency of ~7% by a very precise control of composition while a representative CdS/CdSe from chemical bath deposition have done ~5% with polysulfide electrolytes. In the near future, it is necessary to carry out systematic investigations for developing new hole-conducting materials and controlling interfaces within the cell, thus leading to an enhancement of both open-circuit voltage and fill factor while keeping the current high value of photocurrents from QDs towards more efficient and stable QD-sensitized solar cells.