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Shin, Dongguen,Kang, Donghee,Lee, Jae-Bok,Ahn, Jong-Hyun,Cho, Il-Wook,Ryu, Mee-Yi,Cho, Sang Wan,Jung, Na Eun,Lee, Hyunbok,Yi, Yeonjin American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.18
<P>The interfacial properties of organolead halide perovskite solar cells (PSCs) affect the exciton and charge-transport dynamics significantly. Thus, proper modification of the interfaces between perovskite and charge-transport layers is an efficient method to increase the power conversion efficiency (PCE) of PSCs. In this work, we explore the effect of a nonionic surfactant, that is, Triton X-100 (TX) additive, in the poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) hole-transport layer. The electronic structure of TX-modified PEDOT:PSS is investigated with ultraviolet/X-ray photoelectron spectroscopy and X-ray absorption spectroscopy with various TX concentrations. The surface of the TX-modified PEDOT:PSS layer showed high TX content, and thus the semimetallic properties of PEDOT:PSS were suppressed conspicuously by its insulating nature. With the TX-modified PEDOT:PSS, the PCE of methylammonium lead iodide (MAPbI<SUB>3</SUB>) PSCs increased significantly. To elucidate the origin of the improved device performance, the electrical properties and photoluminescence were investigated comprehensively. Consequently, it was found that the TX additive inhibits interface recombination between PEDOT:PSS and MAPbI<SUB>3</SUB>, which is caused by the suppression of semimetallic properties of the PEDOT:PSS surface. Hence, we fabricated flexible PSCs successfully using a graphene electrode and TX-modified PEDOT:PSS.</P> [FIG OMISSION]</BR>
Interfacial energy level alignments between low-band-gap polymer PTB7 and indium zinc oxide anode
Shin, Dongguen,Lee, Jeihyun,Park, Soohyung,Jeong, Junkyeong,Seo, Ki-Won,Kim, Hyo-Joong,Kim, Han-Ki,Choi, Min-Jun,Chung, Kwun-Bum,Yi, Yeonjin JAPAN SOCIETY OF APPLIED PHYSICS 2015 Applied physics express Vol.8 No.9
Improved Stability of Interfacial Energy-Level Alignment in Inverted Planar Perovskite Solar Cells
Im, Soeun,Kim, Wanjung,Cho, Wonseok,Shin, Dongguen,Chun, Do Hyung,Rhee, Ryan,Kim, Jung Kyu,Yi, Yeonjin,Park, Jong Hyeok,Kim, Jung Hyun American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.22
<P>Even though poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been commonly used as a hole extraction layer (HEL) for p-i-n perovskite solar cells (PSCs), the cells’ photovoltaic performance deteriorates because of the low and unstable work functions (WFs) of PEDOT:PSS versus those of a perovskite layer. To overcome this drawback, we synthesized a copolymer (P(SS-<I>co</I>-TFPMA)) ionomer consisting of PSS and tetrafluoropropylmethacrylate (TFPMA) as an alternative to conventional PEDOT:PSS. The PEDOT:P(SS-<I>co</I>-TFPMA) copolymer solution and its film exhibited excellent homogeneity and high phase stability compared with a physical mixture of TFPMA with PEDOT:PSS solution. During spin coating, a self-organized conducting PEDOT:P(SS-<I>co</I>-TFPMA) HEL evolved and the topmost PEDOT:P(SS-<I>co</I>-TFPMA) film showed a hydrophobic surface with a higher WF compared to that of the pristine PEDOT:PSS film because of its chemically bonded electron-withdrawing fluorinated functional groups. Interestingly, the WF of the conventional PEDOT:PSS film dramatically deteriorated after being coated with a perovskite layer, whereas the PEDOT:P(SS-<I>co</I>-TFPMA) film represented a relatively small influence. Because of the superior energy-level alignment between the HEL and a perovskite layer even after the contact, the open-circuit voltage, short-circuit current, and fill factor of the inverted planar p-i-n PSCs (IP-PSCs) with PEDOT:P(SS-<I>co</I>-TFPMA) were improved from 0.92 to 0.98 V, 18.96 to 19.66 mA/cm<SUP>2</SUP>, and 78.96 to 82.43%, respectively, resulting in a 15% improvement in the power conversion efficiency vs that of IP-PSCs with conventional PEDOT:PSS. Moreover, the IP-PSCs with PEDOT:P(SS-<I>co</I>-TFPMA) layer showed not only improved photovoltaic performance but also enhanced device stability due to hydrophobic surface of PEDOT:P(SS-<I>co</I>-TFPMA) film.</P> [FIG OMISSION]</BR>
Sohyun Park,Hyunchan Lee,Hyunbok Lee,Dongguen Shin,Yeonjin Yi 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.2
Recently, organolead halide perovskites have demonstrated excellent performance in solar cell application. For efficient perovskite solar cells, a uniform and dense perovskite film should be fabricated. A popular method to obtain such film is anti-solvent dripping during the intermediate phase formation. This dripping should be performed at the certain delay time after the spin start. The change in delay time could impact defect formation, significantly varying the electronic structure. The electronic structure of a perovskite film plays a crucial role in the charge transport and recombination in the devices. Thus, the determination of the electronic structure is of major significance to analyze the device performance. In this study, we investigated the electronic structure of methylammonium lead triiodide films fabricated with the different delay time of diethyl ether (DE) dripping. The core level and the valence band were measured using X-ray and ultraviolet photoelectron spectroscopy. As the DE dripping delay time increases, the I/N ratio increases while the work function decreases. This would be attributed to the n-doping effect by the positively charged I-interstitial defect formation.
Jeong, Junkyeong,Kang, Donghee,Chun, Do Hyung,Shin, Dongguen,Park, Jong Hyeok,Cho, Sang Wan,Jeong, Kwangho,Lee, Hyunbok,Yi, Yeonjin Elsevier 2019 APPLIED SURFACE SCIENCE - Vol.495 No.-
<P><B>Abstract</B></P> <P>Direct evidence of chemical interaction and origin of electron accumulation at a “buried” methylammonium lead triiodide (CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB>, hereafter “MAPI”)/TiO<SUB>2</SUB> interface is presented in this study for the first time. Despite the high power conversion efficiency of perovskite solar cells (PSCs) using a TiO<SUB>2</SUB> electron transport layer, the MAPI/TiO<SUB>2</SUB> interface is believed as an electron accumulation position during device operation. To elucidate the cause of the electron accumulation, the energy level alignment at the MAPI/TiO<SUB>2</SUB> interface should be understood. However, a buried MAPI/TiO<SUB>2</SUB> interface forms after a thick MAPI layer deposition; thus, the electronic structure of the MAPI/TiO<SUB>2</SUB> interface cannot be measured using surface-sensitive photoelectron spectroscopy in a conventional stack-up manner. In this study, we investigated the electronic structure of a buried MAPI/TiO<SUB>2</SUB> interface by removing the MAPI and organic layers using solvent immersion. As a result, we reveal that a conduction band minimum (CBM) mismatch occurs owing to the TiOPb bonding on the TiO<SUB>2</SUB> surface. The TiOPb bonds form by the Pb ions penetrating during the spin coating of the MAPI solution. When a [6,6]-phenyl C<SUB>61</SUB> butyric acid methyl ester (PCBM) layer was inserted, the CBM mismatch was removed owing to the high work function of PCBM.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The electronic structure of a buried MAPI/TiO<SUB>2</SUB> interface was investigated. </LI> <LI> The TiOPb bonding on the TiO<SUB>2</SUB> surface occurred after MAPI deposition. </LI> <LI> The CBM mismatch was observed owing to the TiOPb bond formation. </LI> <LI> With PCBM, the cascaded CBM was formed owing to its high work function. </LI> <LI> The cascaded CBM significantly improved the solar cell performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>