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Byranvand, Mahdi Malekshahi,Song, Seulki,Pyeon, Limok,Kang, Gyeongho,Lee, Gang-Young,Park, Taiho unknown 2017 Nano energy Vol.34 No.-
<P><B>Abstract</B></P> <P>We report a simple post annealing-free (PAF) method for making uniform, large grain-sized, and highly crystalline triple cation perovskite films. In this simple process, a perovskite precursor solution was spin-coated onto a TiO<SUB>2</SUB> mesoporous substrate and as an antisolvent, diethyl ether (DEE) was subsequently dripped onto the film during spinning to produce an intermediate phase (IP) of perovskite film. This IP was immediately immersed into a DEE bath at room temperature for only 1min in replacement of the conventional post annealing (PA) treatment. The as-prepared PAF film was characterized by X-ray powder diffraction, UV–vis absorption spectroscopy, fourier transform infrared spectroscopy, scanning electron microscopy, atomic-force microscopy, and photoluminescence spectroscopy. The overall power conversion efficiency (PCE) of the PAF devices was in the range of 18.8–19.5%, which is comparable with the reported PA devices (17.2–18.1%), mainly due to the <I>J</I> <SUB>SC</SUB> and the <I>FF</I> values, caused by the high absorption ability and the large crystal size with better surface smoothness in the PAF film. This efficiency is the highest reported for perovskite deposition by PAF methods. This new method enables reducing the device fabrication time at room temperature, which will reduce the cost of manufacturing efficient perovskite solar cells.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Post annealing-free method is proposed to make high quality perovskite. </LI> <LI> Quality of perovskite by this method is depended on intermediate phase (IP). </LI> <LI> Short time, larger crystal size and smoother surface of PAF film was obtained. </LI> <LI> The performance of the device fabricated using this technique was 19.5%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Lee, Junwoo,Malekshahi Byranvand, Mahdi,Kang, Gyeongho,Son, Sung Y.,Song, Seulki,Kim, Guan-Woo,Park, Taiho American Chemical Society 2017 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.139 No.35
<P>In addition to having proper energy levels and high hole mobility (A) without the use of dopants, hole transporting materials (HTMs) used in n-i-p-type perovskite solar cells (PSCs) should be processed using green solvents to enable environmentally friendly device fabrication. Although many HTMs have been assessed, due to the limited solubility of HTMs in green solvents, no green-solvent-processable HTM has been reported to date. Here, we report on a greensolvent-processable HTM, an asymmetric D-A polymer (asyPBTBDT) that exhibits superior solubility even in the green solvent, 2-methylanisole, which is a known food additive. The new HTM is well matched with perovskites in terms of energy levels and attains a high mu(h) (1.13 x 10(-3) cm(2)/(V s)) even without the use of dopants. Using the HTM, we produced robust PSCs with 18.3% efficiency (91% retention after 30 days without encapsulation under 50%-75% relative humidity) without dopants; with dopants (bis(trifluoromethanesulfonyl) imide and tert-butylpyridine, a 20.0% efficiency was achieved. Therefore, it is a first report for a green-solvent-processable hole-transporting polymer, exhibiting the highest efficiencies reported so far for n-i-p devices with and without the dopants.</P>
Kim, Guan-Woo,Kang, Gyeongho,Malekshahi Byranvand, Mahdi,Lee, Gang-Young,Park, Taiho American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.33
<P>We demonstrate a simple and facile way to improve the efficiency and moisture stability of perovskite solar cells using commercially available hole transport materials, 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD) and poly(3-hexylthiophene) (P3HT). The hole transport layer (HTL) composed of mixed spiro-OMeTAD and P3HT exhibited favorable vertical phase separation. The hydrophobic P3HT was more distributed near the surface (the air atmosphere), whereas the hydrophilic spiro-OMeTAD was more distributed near the perovskite layer. This vertical separation resulted in improved moisture stability by effectively blocking moisture in air. In addition, the optimized composition of spiro-OMeTAD and P3HT improved the efficiency of the solar cells by enabling fast intramolecular charge transport. In addition, a suitable energy level alignment facilitated charge transfer. A device fabricated using the mixed HTL exhibited enhanced performance, demonstrating 18.9% power conversion efficiency and improved moisture stability.</P>
Lee, Junwoo,Lee, Tack Ho,Byranvand, Mahdi Malekshahi,Choi, Kyoungwon,Kim, Hong Il,Park, Sang Ah,Kim, Jin Young,Park, Taiho The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.14
<P>In this study, we demonstrated the effects of the molecular weight (MW) of a green-solvent processable semiconducting polymer (asy-PBTBDT) on its photovoltaic performance and device thermal stability in green processed devices for the first time. The asy-PBTBDT with a high MW (132 kDa) had the highest <I>μ</I>h values (4.91 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> without dopants and 5.77 × 10<SUP>−3</SUP> cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> with dopants) as a result of increase in the π-π stacking along with MW as compared to low-MW asy-PBTBDTs (27 and 8 kDa). The high-MW asy-PBTBDT with a high <I>μ</I>h achieved the best power conversion efficiencies of 18.2% and 20.0% for the undoped and doped states in PerSCs, respectively, and 5.7% in PSCs in green processed devices. Furthermore, the glass transition temperature increased with an increase in MW; this indicated an effective decrease in heat-induced morphological degradation in the photovoltaic devices. In addition, an increase in the chain density along with MW led to good robustness against humidity and oxygen.</P>