Yun Kyung Jung

Single-Crystal-like Perovskite for High-Performance Solar Cells Using the Effective Merged Annealing Method

We report a simple, low cost, and quite effective method for achieving single-crystal-like CH3NH3PbI3 perovskite leading to a significant enhancement in the performance and stability of inverted planar perovskite solar cells (IPSCs). By employing a merged annealing method during the fabrication of an IPSC for preparing the perovskite CH3NH3PbI3 film, we remarkably increase the crystallinity of the CH3NH3PbI3 film and enhance the device performance and stability. An IPSC with the indium tin oxide/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/CH3NH3PbI3 (active layer)/[6,6]-phenyl-C61-butyric acid methyl ester/Al structure was fabricated using the merged annealing method and exhibited significantly enhanced performance with a high power conversion efficiency of 18.27% and a fill factor of 81.34%. Moreover, since two separate annealing processes are merged in the proposed annealing method, the fabrication step becomes much simpler and easier, leading to a reduction in fabrication costs.

Pyrrole N-alkyl side chain effects on the properties of pyrrolo[3,4-c]pyrrole-1,3-dione-based polymers for polymer solar cells

In this study, two new pyrrolo[3,4-c]pyrrole-1,3-dione (PPD)-based polymers (P3 and P4) incorporating a 2-octyldodecyl (branched alkyl) group on the pyrrole nitrogen of the PPD unit were prepared. Their properties were briefly compared to those of the structurally quite similar PPD-based polymers (P1 and P2) with an n-octyl (linear alkyl) group on the PPD unit, in order to understand the importance of the pyrrole N-alkyl group. The calculated optical band gaps (Eg) and highest occupied molecular orbital energy levels of P3 and P4 were found to be around ∼0.1 eV higher and deeper, respectively, compared to those of the respective linear alkylated polymers P1 and P2. The maximum power conversion efficiency (PCE) obtained for the polymer solar cells made by using P3 or P4:PC70BM blends without any additive was around ∼2%, which was quite similar to that of the PSCs made using P1 or P2:PC70BM blends. However, P3 and P4 exhibited a notably lower PCE than that of P1 and P2, respectively, when the polymer solar cells were created with an additive. This study confirmed that the alkyl substituent on the pyrrole nitrogen of the PPD unit significantly affects the properties of the resulting polymer.

Understanding and Tailoring Grain Growth of Lead-Halide Perovskite for Solar Cell Application

The fundamental mechanism of grain growth evolution in the fabrication process from the precursor phase to the perovskite phase is not fully understood despite its importance in achieving high-quality grains in organic-inorganic hybrid perovskites, which are strongly affected by processing parameters. In this work, we investigate the fundamental conversion mechanism from the precursor phase of perovskite to the complete perovskite phase and how the intermediate phase promotes growth of the perovskite grains during the fabrication process. By monitoring the morphological evolution of the perovskite during the film fabrication process, we observed a clear rod-shaped intermediate phase in the highly crystalline perovskite and investigated the role of the nanorod intermediate phase on the growth of the grains of the perovskite film. Furthermore, on the basis of these findings, we developed a simple and effective method to tailor grain properties including the crystallinity, size, and number of grain boundaries, and then utilized the film with the tailored grains to develop perovskite solar cells.

Highly crystalline new benzodithiophene–benzothiadiazole copolymer for efficient ternary polymer solar cells with an energy conversion efficiency of over 10%

A new alternating polymer P(BDTSi–DFBT), poly(4,8-bis(triisopropylsilylethynyl)-benzo[1,2-b:4,5-b′]dithiophene-alt-5,6-difluoro-4,7-bis(4-octylthiophen-2-yl)benzo[c][1,2,5]thiadiazole), was prepared via Stille polymerization. The determined absorption maximum and optical band-gap (Eg) of P(BDTSi–DFBT) were 590 nm and 1.74 eV, respectively. The calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels of P(BDTSi–DFBT) were −5.45 eV and −3.71 eV, respectively. The X-ray diffraction (XRD) analysis confirmed that P(BDTSi–DFBT) is a crystalline polymer. The binary-polymer solar cells, ITO/PEDOT:PSS/P(BDTSi–DFBT)u2006:u2006PC70BM (1u2006:u20061.5 wt%) + 3 vol% DIO/Al, made from P(BDTSi–DFBT) gave a power conversion efficiency (PCE) of 5.02% with an open-circuit voltage (Voc) of 0.81 V, a short-circuit current (Jsc) of 11.68 mA cm−2, and a fill factor (FF) of 53%. Conversely, the ternary-polymer solar cells, ITO/PEDOT:PSS/PTB7-Thu2006:u2006P(BDTSi–DFBT)u2006:u2006PC70BM (0.8u2006:u20060.2u2006:u20061.5 wt%) + 3 vol% DIO/Al, made with a synthesized medium band-gap P(BDTSi–DFBT) and low band-gap PTB7-Th, offered a maximum PCE of 10.05%, with a Voc of 0.79 V, a Jsc of 17.92 mA cm−2, and a FF of 71%.

Bulk Heterojunction-Assisted Grain Growth for Controllable and Highly Crystalline Perovskite Films

Perovskite optoelectronic devices are being regarded as future candidates for next-generation optoelectronic devices. Device performance has been shown to be influenced by the perovskite film, which is determined by the grain size, surface roughness, and film coverage; therefore, developing controllable and highly crystalline perovskite films is pivotal for highly efficient devices. In this work, an innovative bulk heterojunction (BHJ)-assisted grain growth (BAGG) technique was developed to accurately control the quality of perovskite films. By a simple modulation of the polymer-to-PC61BM ratio in the BHJ film, the transition to a complete film phase from the perovskite precursor was accurately regulated, resulting in a controllable perovskite grain growth and high-quality final perovskite film. Moreover, because the BHJ layer could seep deeply into the perovskite active layer through the grain boundaries in the BAGG process, it facilitated the interface engineering and charge transport. The perovskite solar cells containing an optimized CH3NH3PbI3 film presented a high efficiency of 18.38% and fill factor of 83.71%. The perovskite light-emitting diode that contained a nanoscale and uniform CH3NH3PbBr3 film with full coverage presented enhanced emission properties with a brightness value of 1600 cd/m2 at 6.0 V and a luminous efficiency of 0.56 cd/A.