Small Molecule Organic Photovoltaic Modules Fabricated via Halogen-Free System with Roll-to-Roll Compatible Scalable Printing Method

Abstract

Organic conjugated molecules have a great potential for cost-competitive, large-area and high throughput mass production on mechanically flexible substrate. In particular, small molecule, which is one of the organic conjugated molecules, have several distinct advantages such as well-defined molecular structure, high purity, and less batch-to-batch variation. During recent years, organic solar cells based on the small molecules have accomplished considerable progress, reaching the PCEs over 10%. Now, for further advances in this field, printed or halogen free fabricated small molecule solar cells should be also demonstrated. In this study, blend films of small molecules, benzodithiophene terthiophene rhodanine (BTR) and PC71BM were slot-die coated using a halogen-free solvent system. Moreover, for up-scaling production, we fabricated small molecule solar cells with not only time-consuming solvent vapor annealing (SVA) treatment but also more roll-to-roll compatible solvent additive approaches. The suitability of halogen-free additive method for up-scaling production was analyzed by using UV-vis absorption, EQE, AFM, TEM, SCLC, Light intensity and 2D-GIWAXS measurements. As a result, high efficiencies of 7.46% and 6.56% were achieved from time-consuming solvent vapor annealing (SVA) treatment and roll-to-roll compatible solvent additive approaches, respectively. After successful verification of our roll-to-roll compatible additive method on small-area devices, we finally demonstrated large-area photovoltaic modules composed of 4 stripes with a total active area of 10 cm2, achieving a power conversion efficiency (PCE) of 4.8%.