Insoo Shin

Tandem solar cells made from amorphous silicon and polymer bulk heterojunction sub-cells.

A tandem solar cell based on a combination of an amorphous silicon (a-Si) and polymer solar cell (PSC) is demonstrated. As these tandem devices can be readily fabricated by low-cost methods, they require only a minor increase in the total manufacturing cost. Therefore, a combination of a-Si and PSC provides a compelling solution to reduce the cost of electricity produced by photovoltaics.

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.

Modulation of the properties of pyrrolo[3,4-c]pyrrole-1,4-dione based polymers containing 2,5-di(2-thienyl)pyrrole derivatives with different substitutions on the pyrrole unit

In this study, four new pyrrolo[3,4-c]pyrrole-1,4-dione (DKPP)-based polymers, P(DKPP-TPTH), P(DKPP-TPTE), P(DKPP-TPTA), and P(DKPP-TPTI), containing N-alkyl-2,5-di(2-thienyl)pyrrole (TPT) derivatives with four different substituents such as hydrogen, ester, amide, and imide groups on the 3,4-position of the pyrrole unit were prepared to tune the properties of the polymers. Opto-electrical studies showed that the incorporation of electron withdrawing substituents such as ester, amide and imide groups instead of hydrogen into the pyrrole backbone of the polymers increased the band gaps significantly from 1.31 eV to 1.42 eV, 1.37 eV and 1.37 eV, respectively, and reduced the highest occupied/lowest unoccupied molecular orbital (HOMO/LUMO) energy levels from −4.96 eV/−3.65 eV to −5.24 eV/−3.82 eV, −5.17 eV/−3.80 eV and −5.35 eV/−3.98 eV, respectively. Organic field effect transistors (OFETs) made from these polymers indicated that the incorporation of electron withdrawing functional groups into the polymer backbone reduced hole mobility. Polymer solar cells (PSCs) prepared using polymers as electron donors offered higher power conversion efficiency (PCE) for the polymer containing hydrogen on the TPT backbone, but the polymers incorporating electron withdrawing substituents into the TPT backbone showed a significantly higher open-circuit voltage (Voc) though the PCE was relatively low.

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.

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.

Effective methods for improving device performances of P-I-N perovskite solar cells

In this presentation, we report a simple and effective method for improving the performance of CH3NH3PbI3 perovskite solar cells. By employing a novel hot-air annealing process (HAAP) and a merged annealing method (MA) for preparing the perovskite CH3NH3PbI3 film, we could successfully enhance the crystallinity of the CH3NH3PbI3 active layer and improve its photon collection properties. This led to a marked improvement in device performance. Solar cells with the structure indium tin oxide/poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate)/CH3NH3PbI3 active layer/[6,6]-phenyl-C61-butyric acid methyl ester/Ca/Al and fabricated using these methods showed significantly improved performance, including higher PCE and fill factor values than those of the device fabricated conventionally. The PCE increased from 9.05 to 15.55 % when the HAAP process was used and to 18.55 % when the MA was used. Moreover, the devices did not exhibit photocurrent hysteresis, which is always observed in the case of the conventionally fabricated solar cells owing to the charge traps resulting from the low quality of the perovskite film.