Won Jun Jo
The demand for more efficient and eco-friendly energy harvest technology is growing rapidly, especially in response to global warming and natural resource depletion. Therefore, high-performance solar energy conversion systems toward a fossil fuel-free and sustainable future are of paramount importance in both academia and industry.1,2 In this regard, organic solar cells (OSCs) offer the promise of lightweight, flexible, large-area, and cost-effective photovoltaic technology. However, they are not efficient and stable enough to achieve commercialization worldwide. To address these challenges, we adopted oxidative chemical vapor deposition (oCVD) as a key polymer thin-film integration strategy into OSCs. oCVD is a solvent-free vacuum-based technique to enable substrate-independent conformal thin-film fabrication of diverse insoluble conducting and semiconducting polymers, which are very difficult to process by typical solution-based methods. Further, oCVD carries commercialization-critical benefits, such as parallel and sequential deposition, well-defined thickness control, large-area uniformity, and compatibility with other standard vacuum technologies.3-6 Based on the strengths of oCVD, we have successfully developed various polymer thin films with desirable properties, patterns, and size to apply them to OSCs. First, we used oCVD PEDOT thin films as polymer electrodes for OSCs.3 Second, we incorporated polyselenophene donor layers into OSCs for the first time.4 Third, we created neutral polymeric hole-transporting layers, also for the first time, by integrating patterned Cl doped poly(3,4-dimethoxythiophene) thin films into OSCs.5 Because this novel polymer has neutrality, high transparency, good conductivity, and appropriate energy levels, the solar cell efficiency and lifetime are remarkably improved compared to conventional OSCs.5 To upgrade the efficiency and lifetime further, we have recently realized the new concept of a photoactive, hole-transporting, and neutral polymer by using oCVD polythiophene.6,7 Considering oCVD functions independent of material solubility and substrate properties, the progress made by oCVD polymers can be readily extended to perovskite solar cells. This opens new possibilities for printable and flexible photovoltaics by enhancing their efficiency and lifetime.