Large-scale programmable assembly of functional microcomponents for advanced electronics via light-regulated adhesion and polymer growth

Large-area,programmable assembly of diverse micro-objects onto arbitrary substrates is a fundamental yet challenging task.Herein a simple wafer-level micro-assembly technique based on the light-triggered change in both surface topography and interfacial adhesion of a soft photo-sensitive polymer is proposed.In particular,the light-regulated polymer growth creates locally indented and elevated zones on the stamp surface.The light-mediated adhesion reduction,on the other hand,facilitates the inks to be released from the polymer.The interplay of these two effects makes it feasible for the programmable assembly of ultra-small components onto various substrates coated with supplementary adhesive layers.The fidelity of this technique is validated by assembling diverse materials and functional devices,with the printing size up to 4-inch.This work provides a rational strategy for large-scale and programmable assembly of diverse delicate micro-objects,bypassing the common issues of some existing techniques such as poor transfer uniformity,small printing area,and high cost.

Constructing vertical phase separation of polymer blends via mixed solvents to enhance their photovoltaic performance

A polymer blend comprising poly(3-hexylthiophene)(P3HT)donor and poly[2,7-(9,9′-octyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-5′,6′-bis(hexyloxy)-2′,1′,3′-benzothiadiazole)](PFDTBT-OC6)acceptor is used as the active layer to fabricate all-polymer solar cells.The blend morphology variance processed with pure and mixed solvents,and the related photovoltaic performance,are investigated in detail.It is found that,due to its low surface energy,a thin P3HT enrichment layer on the top surface of the active layer greatly increases bimolecular recombination and results in S-kinks of the illuminated current density-voltage curves.With the incorporation of p-xylene(a marginal solvent of P3HT)in the blend solution,the P3HT enrichment atop the active layer surface is effectively decreased because the high boiling-point p-xylene suppresses the diffusion of P3HT chains toward the top surface during the film-drying process.The bimolecular recombination was thus improved and the S-kinks of the photovoltaic curves were completely removed.The overall power conversion efficiencies of the devices are strongly boosted(from 0.88%to 1.41%)when chlorobenzene:p-xylene mixed solvent is used to replace pure chlorobenzene.