Roll-to-Roll Slot-Die-Printed Polymer Solar Cells by Self-Assembly

Efficient Non-Fullerene Organic Photovoltaics Printed by Electrospray via Solvent Engineering

Developing scalable processing methods with low material waste is still one of the remaining challenges for organic photovoltaics (OPVs) to become a practical renewable energy source. Here, we report the first study on printing active layers of OPVs containing non-fullerene acceptors (NFAs) by electrospray (ES). The properties of the solvent significantly influence the interfacial morphology of ES-printed organic thin-films, and solvent engineering is essential to facilitate the formation of efficient active-layer films. We introduce low-vapor-pressure non-halogen solvent o-xylene (OXY) into the high vapor pressure solvent of chloroform to form a binary solvent system with appropriate evaporation time, electric conductivity, and solubility. The characteristic times of the ES process using binary solvents are quantified to provide insights into the dynamic formation of thin films. A longer droplet evaporation time with decent solubility collectively decrease the roughness and domain size of the polymer/NFA blend films, thus increase the photocurrent and fill factor of the ES-printed OPV devices. The ES-printed active layers show enhanced crystallinity and phase separation of NFA molecules than the spin-coated films. The champion cell with an ES-printed PTB7-Th:FOIC active layer exhibits a power conversion efficiency of 9.45%, which is on par with the spin-coated cells and is among the highest of spray-deposited organic solar cells to date. This work demonstrates that ES is an effective method to prepare OPVs on NFAs.

Soft Porous Blade Printing of Nonfullerene Organic Solar Cells

Developing scalable and robust processing methods with low material waste remains a challenge for organic solar cells (OSCs) to become a practical renewable energy source. Here, we present a novel low-cost processing approach termed as soft porous blade printing (SPBP), which uses a layer of soft porous material such as filter paper as the printing blade. The inherent porous microstructure of the blade offers high shear rates that facilitate the alignment, crystallization, and orientation of active materials during printing. Moreover, by eliminating the suspended liquid meniscus, SPBP relaxes the stringent requirement of gap control and enables continuous ink delivery for uninterrupted film fabrication with adjustable thickness. Higher photovoltaic performances are achieved in the SPBP-printed OSCs than those of the spin-coated counterparts for two nonfullerene-acceptor active-layer systems (Y6:PM6 and PTQ10:IDIC). Y6:PM6 cells printed by SPBP without any additive exhibit power conversion efficiencies up to 14.75%, which is among the highest reported to date for non-spin-coated OSCs.

Processing-Friendly Slot-Die-Cast Nonfullerene Organic Solar Cells with Optimized Morphology

The power conversion efficiencies (PCEs) of spin-coated organic solar cells (OSCs) have increased rapidly in recent years. However, spin-coating shows poor reproducibility for large-scale production. Slot-die coating, a lab-scale version of roll-to-roll fabrication, has been considered as the most suitable technique for the production of future large-area commercial devices. For this, the highly efficient slot-die-fabricated devices are required to approach the performance of spin-cast OSCs. We present here, a nonfullerene OSC device utilizing the PBDB-T/i-IEICO-4F blend, fabricated by slot-die coating without post-treatment in the ambient conditions. The device showed an impressive PCE of 12.5%, which is one of the highest reported performance for slot-die-coated OSC devices. Compared to the spin-coated and blade-coated films with optimized thermal annealing time, the films fabricated by slot-die coating (without any treatment) exhibit not only the highest degree of crystallinity and face-on orientation but also the smallest domain size and the purest phase toward enhanced and balanced carrier mobilities. An enhanced excited-state charge generation has been attributed to transient charge kinetics using ultrafast spectroscopic signatures. The optimized slot-die-coated devices exhibit excellent tolerance for the increased thickness of the photoactive layer, attributing to favorable molecular packing. We used slot-die coating as a simple fabrication technique, which is capable of yielding highly efficient OSCs.

A General Approach for Lab-to-Manufacturing Translation on Flexible Organic Solar Cells

The blossoming of organic solar cells (OSCs) has triggered enormous commercial applications, due to their high-efficiency, light weight, and flexibility. However, the lab-to-manufacturing translation of the praisable performance from lab-scale devices to industrial-scale modules is still the Achilles' heel of OSCs. In fact, it is urgent to explore the mechanism of morphological evolution in the bulk heterojunction (BHJ) with different coating/printing methods. Here, a general approach to upscale flexible organic photovoltaics to module scale without obvious efficiency loss is demonstrated. The shear impulse during the coating/printing process is first applied to control the morphology evolution of the BHJ layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot-die printing and spin-coating is detected. Compelling results of morphological evolution, molecular stacking, and coarse-grained molecular simulation verify the validity of the impulse translation. Accordingly, the efficiency of flexible devices via slot-die printing achieves 9.10% for PTB7-Th:PC₇₁ BM and 9.77% for PBDB-T:ITIC based on 1.04 cm² . Furthermore, 15 cm² flexible modules with effective efficiency up to 7.58% (PTB7-Th:PC₇₁ BM) and 8.90% (PBDB-T:ITIC) are demonstrated with satisfying mechanical flexibility and operating stability. More importantly, this work outlines the shear impulse translation for organic printing electronics.