The Interfacial Investigation Of Polymer And Perovskite Solar Cells

Polymer and perovskite solar cells have attracted much attention and been investigated extensively due to their flexibility, low-cost and simple processibility. It is found that the key photovoltaic processes:charge dissociation, charge transport and charge collection, are closely relativ to the interface characteristics. As we all know, the interface is a dynamic parameter under device working condition. However, the traditional experimental tools, such as UPS, XPS and SKPM, can only explore the static interface under device non-working condition. In this thesis, we have investigated the dynamic interfacial characteristics and the relationship between the bulk and the electrode interface under device working condition by utilizing the in-situ experimental tools:the Light-assisted Dielectric Responses (LADRs), Electric field-modulated Magnetic Field Effects of the photocurrent (E-MFEpc), Electric field-modulated photoluminescence (E-PL), Optical field-modulated Current-voltage characteristics (O-CV). The work is concluded as followed:(1) The efficient polymer solar cells were fabricated by matching the HOMO energy level for donors and the LUMO energy level for acceptors. It is found that the HOMO energy level of donors can affect the interfacial charge accumulation obviously, while the LUMO energy level of acceptors almost has no influence on it. It concludes that the holes would be a much contribution to the interfacial charge accumulation in polymer solar cells. The potential energy difference at the electrode interface plays an important role in controlling the charge collection. This work provides a direct experimental basis for device design.(2) The polymer solar cells based on the PBTTPD:PCBM with PEDOT:PSS of varied thickness were fabricated. It is found that they have different interfacial charge accumulation by using LADRs. The E-MFEpc results show that it has larger binding energy for charge transfer complexes (CTs) in the devices with more interfacial charge accumulation. It is indicated that the interface electric field in opposite direction to the built-in electric field induced by the interfacial charge accumulation would increase the binding energy of CTs at the donor:acceptor interface, decreasing the charge dissociation. This study reveals the influence rules of interfacial electric field on the charge seperation.(3) The factors affecting the light intensity-dependence of fill factor (FF) were studied: bulk traps, bulk charge recombination and interfacial charge accumulation. It is found that the bulk charge recombination and interfacial charge accumulation are the main factors in the decrease of FF with increasing the light intensity. Meanwhile, the FF of devices with bulk traps would increase and then decrease when the light intensity increases. In addition, the TCNQ is doped in the active layer as the electron traps with different concentration. As a result, in the devices with TCNQ of higher concentration, it needs larger light intensity to reduce the FF in the FF-light intensity curves. This study established a new method to probe the traps in the bulk:the light intensity-dependence of the FF. Compared to other methods, this means is easier.(4) The power conversion efficiency of perovskite solar cells based on the PCBM is increased to14.35%from9.91%after improving the PCBM/Al interface characteristics with the interface dipole materials P2. The devices were fabricated through solution spin-coating methods and vacuum deposition methods. The interfacial dipole induced by P2is probed by using SKPM and O-PL under the device non-working and working condition, respectively. The interfacial dipole can improve bulk charge transport and interfacial charge collection.(5) The photovoltaic processes in the bulk and at the interface are interconnected under device-working condition in polymer and perovskite solar cells. Increasing bulk charge dissociation and transport would enhance the interfacial charge accumulation, while the polarization and charge accumulation at the electrode interface would control the bulk charge seperation and transport through interfacial electric field. This work reveals that the interfacial photovoltaic processes play a crucial factor in the determination of device performance.This dissertation reveals the importance of interfacial electric field on bulk charge dissociation, transport and interface charge extraction under working condition by using the in-situ experimental tools above, and establishs a new method for probing bulk traps and fabricates a highly efficient solar cell devices.