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>

Room-temperature-processed colloidal quantum dot solar cells via chemical modification of ZnO electron transporting layer

Randi AZMI,Havid AQOMA,Sung-Yeon JANG 한국진공학회 2016 한국진공학회 학술발표회초록집 Vol.2016 No.8

High-performance dopant-free conjugated small molecule-based hole-transport materials for perovskite solar cells

Azmi, Randi,Nam, So Youn,Sinaga, Septy,Akbar, Zico Alaia,Lee, Chang-Lyoul,Yoon, Sung Cheol,Jung, In Hwan,Jang, Sung-Yeon Elsevier 2018 Nano energy Vol.44 No.-

<P><B>Abstract</B></P> <P>Hole-transport materials are a crucial element influencing the efficiency, hysteresis, and stability of perovskite solar cells (PSCs). Current state-of-the-art hole-transport materials require additional oxidizing dopants to achieve sufficient hole-transport properties; however, these dopants are environmentally harmful while also deteriorating the stability of PSCs. The development of high-performance dopant-free hole-transport materials is an important goal in the field of PSCs. In this work, we developed novel conjugated small-molecule based dopant-free hole-transport materials for PSCs containing di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole (DBTP) as a core unit. These small molecule hole-transport materials achieved higher hole mobility and interfacial charge transfer rates than optimally doped spiro-OMeTAD, the current-state-of-the-art hole-transport material. A low-temperature PSC device using a dopant-free small molecule hole-transport material displayed a PCE of 18.09% with negligible hysteresis, higher than a device using doped spiro-OMeTAD (17.82%). Notably, the hydrophobic nature of our dopant-free small molecule hole-transport materials afforded excellent air-storage stability of low-temperature PSCs (81% retention after 33 days), whereas the doped spiro-OMeTAD based PSCs rapidly degraded under identical conditions (< 1% retention after 33 days).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel dopant-free hole-transport-materials for perovskite solar cells were developed. </LI> <LI> The face-on orientation enabled sufficiently high hole mobility without dopants. </LI> <LI> Low-temperature PSCs based on the dopant-free HTMs showed the efficiency of 18.09%. </LI> <LI> The dopant-free HTMs acted as passivation layers, providing excellent air stability. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>High-performance dopant-free small molecule hole-transport-materials (SM-HTMs) for perovskite solar cells (PSCs) are developed. The SM-HTMs possess appropriate energy levels with sufficient hole mobility to function as efficient HTM for PSCs without additional dopants. A low-temperature PSC (L-PSC) device using a dopant-free SM-HTM displayed a PCE of 18.09% with high air-storage stability, which is superior to a device using doped spiro-OMeTAD.</P> <P>[DISPLAY OMISSION]</P>

Performance Improvement in Low-Temperature-Processed Perovskite Solar Cells by Molecular Engineering of Porphyrin-Based Hole Transport Materials

Azmi, Randi,Lee, Un-Hak,Wibowo, Febrian Tri Adhi,Eom, Seung Hun,Yoon, Sung Cheol,Jang, Sung-Yeon,Jung, In Hwan American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.41

<P>Porphyrin derivatives have recently emerged as hole transport layers (HTLs) because of their electron-rich characteristics. Although several successes with porphyrin-based HTLs have been recently reported, achieving excellent solar cell performance, the chances to improve this further by molecular engineering are still open. In this work, Zn porphyrin (P<SUB>Zn</SUB>)-based HTLs were developed by conjugating fluorinated triphenylamine (FTPA) wings at the perimeter of the P<SUB>Zn</SUB> core for low-temperature perovskite solar cells (L-PSCs). The fluorinated P<SUB>Zn</SUB>-HTLs (P<SUB>Zn</SUB>-2FTPA and P<SUB>Zn</SUB>-3FTPA) exhibited superior HTL properties compared to the nonfluorinated one (P<SUB>Zn</SUB>-TPA). Moreover, their deeper highest occupied molecular orbital energy levels were beneficial for boosting open-circuit voltages, and their enhanced face-on stacking improved the hole transport properties. The L-PSC using P<SUB>Zn</SUB>-2FTPA achieved the highest performance of 18.85%. Thus far, this result is one of the highest reported power conversion efficiencies among the PSCs using porphyrin-based HTLs.</P> [FIG OMISSION]</BR>

Improved performance of colloidal quantum dot solar cells using high-electric-dipole self-assembled layers

Azmi, Randi,Nam, So Youn,Sinaga, Septy,Oh, Seung-Hwan,Ahn, Tae Kyu,Yoon, Sung Cheol,Jung, In Hwan,Jang, Sung-Yeon Elsevier 2017 Nano energy Vol.39 No.-

<P><B>Abstract</B></P> <P>High performance colloidal quantum dot (CQD) solar cells were developed by modifying ZnO electron accepting layers (EALs) using self-assembled monolayers (SAMs) of highly polar molecules. A high molecular dipole moment of −10.07D was achieved by conjugating a strong electron donor, julolidine, to an electron acceptor, a cyanoacetic acid unit, through a thiophene moiety. The energetic properties of ZnO EALs were manipulated with respect to the dipole moment of the modifying molecules. The built-in potential (<I>V</I> <SUB>bi</SUB>) and internal electric field (<I>E</I> <SUB>int</SUB>) of CQD solar cells could thereby be tuned. The power conversion efficiency (PCE) of the SAM modified devices was improved from 3.7% to 12.9% relative to the unmodified devices as a function of molecular dipole moments (from −5.13D to −10.07D). All figures-of-merit of solar cells were improved simultaneously by SAM modification due to enhanced <I>V</I> <SUB>bi</SUB>, <I>E</I> <SUB>int</SUB>, and charge collection efficiency. The PCE of the highly polar molecule modified devices reached 10.89% with a <I>V</I> <SUB>OC</SUB> of 0.689V, whereas that of the unmodified devices was 9.65% with a <I>V</I> <SUB>OC</SUB> of 0.659V. Notably, the remarkably low energy loss of 0.433eV is achieved in the SAM modified devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> High efficiency colloidal quantum dot solar cells were developed using highly polar SAM modified ZnO electron accepting layers. </LI> <LI> Synthesized novel self-assembling highly polar molecules for electric dipole layer (EDL). </LI> <LI> The solar cell performance was improved by the modification due to enhanced internal electric field and charge collection efficiency. </LI> <LI> The power conversion efficiency of 10.89% with energy loss of 0.433eV was achieved. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>High efficiency colloidal quantum dot solar cells were developed using highly polar SAM modified ZnO electron accepting layers. The solar cell performance was improved by the modification due to enhanced internal electric field and charge collection efficiency. The power conversion efficiency of 10.89% with energy loss of 0.433eV was achieved.</P> <P>[DISPLAY OMISSION]</P>

Simultaneous Improvement in Efficiency and Stability of Low-Temperature-Processed Perovskite Solar Cells by Interfacial Control

Azmi, Randi,Lee, Chang-Lyoul,Jung, In Hwan,Jang, Sung-Yeon Wiley-VCH 2018 ADVANCED ENERGY MATERIALS Vol.8 No.14

<P>In most current state-of-the-art perovskite solar cells (PSCs), high-temperature (approximate to 500 degrees C)-sintered metal oxides are employed as electron-transporting layers (ETLs). To lower the device processing temperature, the development of low-temperature-processable ETL materials (such as solution-processed ZnO) has received growing attention. However, thus far, the use of solutionprocessed ZnO is limited because the reverse decomposition reaction that occurs at ZnO/perovskite interfaces significantly degrades the charge collection and stability of PSCs. In this work, the reverse decomposition reaction is successfully retarded by sulfur passivation of solution-processed ZnO. The sulfur passivation of ZnO by a simple chemical means, efficiently reduces the oxygen-deficient defects and surface oxygen-containing groups, thus effectively preventing reverse decomposition reactions during and after formation of the perovskite active layers. Using the low-temperature-processed sulfurpassivated ZnO (ZnO-S), perovskite layers with higher crystallinity and larger grain size are obtained, while the charge extraction at the ZnO/perovskite interface is significantly improved. As a result, the ZnO-S-based PSCs achieve substantially improved power-conversion-efficiency (PCE) (19.65%) and long-term air-storage stability (90% retention after 40 d) compared with pristine ZnO-based PSCs (16.51% and 1% retention after 40 d). Notably, the PCE achieved is the highest recorded (19.65%) for low-temperature ZnObased PSCs.</P>

High-Efficiency Air-Stable Colloidal Quantum Dot Solar Cells Based on a Potassium-Doped ZnO Electron-Accepting Layer

Azmi, Randi,Seo, Gabseok,Ahn, Tae Kyu,Jang, Sung-Yeon American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.41

<P>High-efficiency colloidal quantum dot (CQD) solar cells (CQDSCs) with improved air stability were developed by employing potassium-modified ZnO as an electron-accepting layer (EAL). The effective potassium modification was achievable by a simple treatment with a KOH solution of pristine ZnO films prepared by a low-temperature solution process. The resulting K-doped ZnO (ZnO-K) exhibited EAL properties superior to those of a pristine ZnO-EAL. The Fermi energy level of ZnO was upshifted, which increased the internal electric field and amplified the depletion region (i.e., charge drift) of the devices. The surface defects of ZnO were effectively passivated by K modification, which considerably suppressed interfacial charge recombination. The CQDSC based on ZnO-K achieved improved power conversion efficiency (PCE) of ≈10.75% (<I>V</I><SUB>OC</SUB> of 0.67 V, <I>J</I><SUB>SC</SUB> of 23.89 mA cm<SUP>-2</SUP>, and fill factor of 0.68), whereas the CQDSC based on pristine ZnO showed PCE of 9.97%. Moreover, the suppressed surface defects of ZnO-K substantially improved long-term stability under air. The device using ZnO-K exhibited superior long-term air storage stability (96% retention after 90 days) compared to that using pristine ZnO (88% retention after 90 days). The ZnO-K-based device also exhibited improved photostability under air. Under continuous light illumination for 600 min, the ZnO-K-based device retained 96% of its initial PCE, whereas the pristine ZnO-based device retained only 67%.</P> [FIG OMISSION]</BR>

High-Efficiency Low-Temperature ZnO Based Perovskite Solar Cells Based on Highly Polar, Nonwetting Self-Assembled Molecular Layers

Azmi, Randi,Hadmojo, Wisnu Tantyo,Sinaga, Septy,Lee, Chang-Lyoul,Yoon, Sung Cheol,Jung, In Hwan,Jang, Sung-Yeon Wiley-VCH 2018 ADVANCED ENERGY MATERIALS Vol.8 No.5

<P>Herein, this study reports high-efficiency, low-temperature ZnO based planar perovskite solar cells (PSCs) with state-of-the-art performance. They are achieved via a strategy that combines dual-functional self-assembled monolayer (SAM) modification of ZnO electron accepting layers (EALs) with sequential deposition of perovskite active layers. The SAMs, constructed from newly synthesized molecules with high dipole moments, act both as excellent surface wetting control layers and as electric dipole layers for ZnO-EALs. The insertion of SAMs improves the quality of PbI2 layers and final perovskite layers during sequential deposition, while charge extraction is enhanced via electric dipole effects. Leveraged by SAM modification, our low-temperature ZnO based PSCs achieve an unprecedentedly high power conversion efficiency of 18.82% with a V-OC of 1.13 V, a J(SC) of 21.72 mA cm(-2), and a FF of 0.76. The strategy used in this study can be further developed to produce additional performance enhancements or fabrication temperature reductions.</P>

Di(1-benzothieno)[3,2-b:2′,3′-d]pyrrole-based Small Molecules for Dopant-free and Efficient Hole Transporting Layer for High Performance Perovskite Solar Cells

강진현,Randi Azmi,김준호,정문기,장성연,정인환 한국고분자학회 2018 한국고분자학회 학술대회 연구논문 초록집 Vol.43 No.2

Structural Effects of Diphenylpyridine Amine-Substituted Porphyrins as Hole Transporting Materials for Perovskite Solar Cells

이운학,Randi Azmi,장성연,정인환,윤성철 한국고분자학회 2017 한국고분자학회 학술대회 연구논문 초록집 Vol.42 No.2