Kilho Yu

Simplified Tandem Polymer Solar Cells with an Ideal Self‐Organized Recombination Layer

A new tandem architecture for printable photovoltaics using a versatile organic nanocomposite containing photoactive and interfacial materials is demonstrated. The nanocomposite forms an ideal self-organized recombination layer via a spontaneous vertical phase separation, which yields a simplified tandem structure fabricated with only four component layers and a high tandem efficiency of 10.8%.

High‐Performance Integrated Perovskite and Organic Solar Cells with Enhanced Fill Factors and Near‐Infrared Harvesting

Highly efficient P-I-N type perovskite/bulk-heterojunction (BHJ) integrated solar cells (ISCs) with enhanced fill factor (FF) (≈80%) and high near-infrared harvesting (>30%) are demonstrated by optimizing the BHJ morphology with a novel n-type polymer, N2200, and a new solvent-processing additive. This work proves the feasibility of highly efficient ISCs with panchromatic absorption as a new photovoltaic architecture and provides important design rules for optimizing ISCs.

In situ studies of the molecular packing dynamics of bulk-heterojunction solar cells induced by the processing additive 1-chloronaphthalene

Processing additives have been widely utilized for high-performance organic bulk-heterojunction (BHJ) photovoltaic devices. However, the role of processing additives remained unclear due to the limited information relying on the final BHJ film state rather than the intermediate film state during solvent evaporation. Here, by using in situ GIWAXS measurements on the intermediate BHJ film, we propose a possible phase separation mechanism in efficient BHJ solar cells consisting of a narrow band gap polymer (P1) and PC71BM via the use of 1-chloronaphthalene (1-CN) as a processing additive. We found that adding small amounts of an additive, 1-CN, with a high boiling point and a high PC71BM solubility can prolong the solvent evaporation time and dissolve many PC71BM molecules, promoting the strong P1 polymer:solvent and PC71BM:solvent interaction to produce pure domains of each component. Thus, the bi-continuous networks for both P1 and PC71BM and their enlarged interfacial area are well fabricated in the BHJ films, inducing balanced photo-charge carrier densities for the electrons and holes and improving the overall photovoltaic performance. Therefore, our findings elucidate the kinetic motions of two organic phases affected by the physical properties of the solvents in the process of film formation and establish criteria for BHJ systems.

Organic Single‐Crystal Semiconductor Films on a Millimeter Domain Scale

Nucleation and growth processes can be effectively controlled in organic semiconductor films through a new concept of template-mediated molecular crystal seeds during the phase transition; the effective control of these processes ensures millimeter-scale crystal domains, as well as the performance of the resulting organic films with intrinsic hole mobility of 18 cm(2) V(-1) s(-1).

Optically transparent semiconducting polymer nanonetwork for flexible and transparent electronics

Significance When various electronic appliances used in everyday life become deformable and transparent, they will provide tremendous versatility in the design and use of see-through, smart mobile applications, exceeding the limitations of the best developed conventional silicon technologies, which are available only in rigid, opaque forms. However, even recently discovered innovative semiconducting components have failed to simultaneously achieve such flexibility and transparency. Thus, the existing options still comprise only hard, planar, or opaque materials, and obtaining a “key” material for creating truly flexible and transparent electronics has presented a formidable challenge. We report an effective means of creating a “truly flexible, perfectly transparent” and high-mobility semiconducting material and demonstrate several high-end flexible and transparent applications based on a polymeric semiconductor system. Simultaneously achieving high optical transparency and excellent charge mobility in semiconducting polymers has presented a challenge for the application of these materials in future “flexible” and “transparent” electronics (FTEs). Here, by blending only a small amount (∼15 wt %) of a diketopyrrolopyrrole-based semiconducting polymer (DPP2T) into an inert polystyrene (PS) matrix, we introduce a polymer blend system that demonstrates both high field-effect transistor (FET) mobility and excellent optical transparency that approaches 100%. We discover that in a PS matrix, DPP2T forms a web-like, continuously connected nanonetwork that spreads throughout the thin film and provides highly efficient 2D charge pathways through extended intrachain conjugation. The remarkable physical properties achieved using our approach enable us to develop prototype high-performance FTE devices, including colorless all-polymer FET arrays and fully transparent FET-integrated polymer light-emitting diodes.

High-efficiency large-area perovskite photovoltaic modules achieved via electrochemically assembled metal-filamentary nanoelectrodes

We devised an electrochemical patterning process for large-area perovskite photovoltaic modules. Realizing industrial-scale, large-area photovoltaic modules without any considerable performance losses compared with the performance of laboratory-scale, small-area perovskite solar cells (PSCs) has been a challenge for practical applications of PSCs. Highly sophisticated patterning processes for achieving series connections, typically fabricated using printing or laser-scribing techniques, cause unexpected efficiency drops and require complicated manufacturing processes. We successfully fabricated high-efficiency, large-area PSC modules using a new electrochemical patterning process. The intrinsic ion-conducting features of perovskites enabled us to create metal-filamentary nanoelectrodes to facilitate the monolithic serial interconnections of PSC modules. By fabricating planar-type PSC modules through low-temperature annealing and all-solution processing, we demonstrated a notably high module efficiency of 14.0% for a total area of 9.06 cm2 with a high geometric fill factor of 94.1%.