미래를 창조하는 포스텍 화학공학과
제목: Interface engineering for high performing organic solar cells
내용: In organic-based photovoltaic cells, aside from improvements in the design and synthesis of active materials, morphology control and interface engineering have emerged as key factors to further increase device efficiency and stability. In early studies on organic solar cells with high conductivity PEDOT:PSS, the contact between ITO and PEDOT:PSS was considered ohmic. However, because low-conductivity PEDOT:PSS (such as AI4083) is mainly utilized in contemporary solar cells, the contact between ITO and PEDOT:PSS is not ohmic anymore. Despite the high possibility that there are serious interface problems, little attention has been paid to the interface between PEDOT:PSS and ITO. Most of the previous studies of interfaces in organic solar cells have focused on the interface between the active and charge transport layers. In this work, we have employed a conjugated polyelectrolyte that uses potassium poly[9,9-bis(3′-sulfonatopropyl)fluorene-alt-(9-(2,7-diethylheptyl)-carboazole)] (WPFSCz-) between ITO and low-conductivity PEDOT:PSS to overcome complicated organic-inorganic interfacial problems. Insertion of the WPFSCz- layer provides substantial advantages in the operation of the polymer solar cells. First, the inserted WPFSCz- layer modifies the work-function of the ITO, thereby forming effective cascading energy alignment, which is favorable for good hole transport. Second, the introduction of the WPFSCz- layer eliminates interfacial trap sites. The reduction in traps reduces recombination losses at the interface, resulting in an improvement in fill factor. These effects result in a significant increase in the efficiency of non-fullerene solar cells based on PM6 and Y6, from 15.86 to 17.34%. In addition, we have found that the problem of the interface in contact with ITO occurs not only in PEDOT:PSS, but also in oxide-based charge transport layers. We have confirmed that insertion of the WPFSCz- layer between ITO and an MoO3(orZnO)chargetransportlayershowsthesamepositiveresults.