Studies On Carrier Dynamics Of Organic Solar Cells Based On Non-fullerene Acceptor Materials

Organic solar cell technology is a key direction for the future development of the photovoltaic industry due to the advantages of potential low cost,excellent device performance and easy to make large-scale flexible devices.Early studies usually employed fullerenes that featured a spherical structure as the electron acceptors.With the continuous deepening of people's understanding of photovoltaic receptor materials,Linear non-fullerene-based acceptors gradually come into the researcher's vision and quickly become a research hotspot.In this thesis,organic solar cell devices were fabricated by using non-fullerene material O-IDTBR as electron acceptor and PTB7-Th as electron donor material.Results from light intensity-variable current density-voltage?J-V?curves show that the filling factor?FF?of the device decreases with the decrease of light intensity.This phenomenon is not the same as the case PC₇₁BM-based device.The FF in PC₇₁BM-based device is almost unchanged under low light intensity.To clarfy the FF-light intensity correlation,AC impedance spectra were applied to analyze of the charge carrier dynamics in the devices.Results indicated that carrier recombination loss in the O-IDTBR device is more serious than that in the device based on PC₇₁BM under low light intensities.Ideality factor analysisand low frequency capacitance-voltage spectra make clear that the ideality factor in the O-IDTBR-based device is much higher than that in the PC₇₁BM devices,Cand charge transport in the PTB7-Th:O-IDTBR based device is blocked at low light intensities.This work would be helpful for the community to have a complete picture of the correlation between fill factor and light intensity.PTB7-Th was chosen as the donor materials for both devices.Although the lowest unoccupied molecular orbital?LUMO?energy levels of the traditional fullerene(PC₇₁BM)and non-fullerene?O-IDTBR?electron acceptors are the same,open circuit voltages of the devices are different.A series of characterizations including impedance spectra,low temperature electrical characterization system,transient photovoltage,and electroluminescent spectra were carried out to investigate the impact of charge carrier recombination and energy disorder on the open-circuit voltage.Specifically,impedance spectra and transient photovoltage measurements indicated that charge recombination in the PC₇₁BM based device was more serious compared with O-IDTBR device.Electroluminescent spectra showed that the PC₇₁BM device had a broader distribution in excited states.A lower open-circuit voltage in the PC₇₁BM device was attributed to more severe charge carrier recombination and high energy disorder.