용액공정 기반의 고효율 이중층 고분자 태양 전지

Abstract

Polymer solar cells (PSCs) based on semiconducting and metallic polymers have drawn considerable attention due to their low cost, flexibility in printable energy devices. PSCs are classified into two types of devices based on the structure of their active layers: simple planar heterojunction (bilayer) and bulk heterojunction (BHJs). BHJ devices consist of a blend of an electron-donating conjugated polymer (P-type) and an electron-accepting fullerene derivative (N-type) in the bulk volume, while bilayer devices consist of sequentially stacked P-type and N-type materials. While the BHJ devices provide greater interfaces of donor and accepting materials, leading to high photocurrent, the bilayer devices are conceptually more straightforward in regard to commercialization. Because the bilayer architecture allows each layer to be controlled and optimized independently, controlling the morphology of each phase is more facile as compared to BHJs. Consequently, the reproducibility of the device performance is increased. Several research groups have demonstrated bilayer SCs including small molecule devices consisting of small molecular donors and fullerene acceptors, in addition to polymer device based on soluble polymer donors and fullerene derivatives acceptors. However, small molecule SCs fabricated by thermal evaporation are hardly regarded as printable SCs, and solution-processable bilayer PSCs exhibit a relatively low power conversion efficiency (PCE) compared to BHJ devices. Therefore, the development of solution-processable bilayer PSCs with a high performance is crucial in order to realize printable SCs and to simultaneously develop useful methods to improve the performance of printable bilayer PSCs. As such, I introduced here two methods to improve the device performance of printable bilayer PSCs: solvent treatment method and processing additive method. After achieving a polymer bilayer structure using an orthogonal solvent, I utilized each method to the bilayer SC and consequently achieved an enhancement in device performances. When the interfaces between the P3HT (Poly[3-hexylthiophene-2,5-diyl]) layer and the PCBM ([6,6]-penyl- C61-butyric-acid-methyl-ester) layer and between the PCBM layer and the Al electrode were treated with ethanol, isopropanol and methanol the bilayer SCs showed significantly enhanced device performance with improved current density (Jsc), fill factor (FF), and PCE. In addition the performances of the bilayer SCs are improved with significantly enhanced Jsc, when I added the DIO (1,8- diiodooctane) additives to the polymer bilayer. Considering these result, it is expected that both methods can be utilized in bilayer PSCs to improve device performance. Moreover, we believe that their utility would be more evident in bilayer structures as compared to BHJ structures because of the additional interface between the donor polymer and fullerene derivatives.