Fabrication And Study Of Polymer Solar Cell Devices Based On Non-fullerene Acceptors

Solution-processable polymer solar cells(PSCs)have attracted considerable interest due to their potential in being light-weight,making flexible and large area devices through printing techniques.However,PSCs are still facing some critical problems for future industrialization:Compared with the silicon and perovskite solar cells,the power conversion efficiency(PCE)of PSCs is still low;The solvent used in the PSCs processing are generally toxic.This paper focus on the problems faced by the industrialization of the PSCs,aiming to reduce the cost and improve the PCEs.Furthermore,in order to promote the application of the PSCs,the green solvent was used in the device fabrication.This paper is mainly divided into the following four parts:1.Polythiophene(PT)derivatives have been intensively studied for application in PSCs due to their advantages of simple synthesis and low cost.PSCs based on the PT and its derivatives as the electron-donor materials didn't achieve higher PCEs because of their narrow light absorption.In this work,we tried to combine ITIC with P3HT and PDCBT to fabricate fullerene-free PSCs,respectively.The morphological studies by atomic force microscopy(AFM),transmission electron microscopy(TEM),and grazing incident wide-angle X-ray scattering(GIWAXS)exhibited that these two polymers had distinctly different aggregation structures in neat films and also in blend films with ITIC.As a result,for the P3HT:ITIC-based PSCs,poor PCE of 1.25%was obtained,but the PDCBT:ITIC-based PSCs demonstrated a remarkable efficiency of 10.16%,which is among the top values in the field of PSCs.2.To get a higher PCE,we successfully fabricate a tandem solar cell(TOSC),and the low-bandgap non-fullerene acceptor,IEICO,was successfully introduced into the rear cell as the long wavelength absorber.Blending with the middle-bandgap conjugated polymer PBDTTT-E-T,the active layer exhibited an impressive photovoltaic response of sunlight irradiation extended to 900 nm.To best modulate the absorption spectrum and harvest a high VOC in tandem cell,the wide-bandgap conjugated polymer PBDD4T-2F and PC71BM were rationally selected into the front cell.an outstanding PCE of 12.80%,with a VOC of 1.71 V,a Jsc of 11.51 mA cm-2,and FF of 0.65,was achieved under the optimized conditions.The results have been certified by the Nation Institute of Metrology,China,which is the top one institute for giving certified results of solar cells.Simultaneously improving Voc and Jsc is a particularly tricky issue for TOSCs,our work demonstrates a great potential of small molecule acceptors in solving this compromise for highly efficient tandem devices and expect to realize better performance in near future.3.Until now,the widely used solvents in PSC fabrication are chlorinated solvents like chloroform(CF),1,2-dichlorobenzene(DCB)and chlorobenzene(CB),because of their strong ability to dissolve organic semiconductors.However,the use of these solvents is restricted in industry because they are highly detrimental to the environment.In this work,we used THF instead CB as the main processing solvents,taking PBDB-T as the reference material,a representative polymer donor in highly efficient NF-PSCs,we successively enlarge its flexible side chains to improve its solubility in THF and its conjugated side groups to enhance its ?-?stacking effect in solid film.As a result,through this two-step optimization in chemical structure,a new polymer PBDB-BzT,the one with a moderate aggregation effect in THF solution and strong ?-? stacking intensity can be obtained,which shows an outstanding PCE of 12.10%in the device,which is slightly higher than that of the reference device.4.In this work,we present a new method to reduce Eloss,of the non-fullerene PSCs.A small molecular material(NRM-1)is synthesized and then blended with a polymer donor PBDB-T and a non-fullerene acceptor IT-4F,respectively.By the measurements of UV-Vis absorption spectroscopy,differential scanning calorimetry(DSC),X-ray diffraction(XRD)and atomic force microscopy(AFM),we prove that NRM-1 has strong tendency to mix with IT-4F without phase separation while it can be separated from the PBDB-T phase.When we added NRM-lto the PBDB-T:IT-4F-based PSCs,Voc of the OSC can be improved from 0.71 to 0.90 V,the PSC shows a 13%improvement compared to the control device without NRM-1.What is more,we validate that this new method is applicable to PSCs based on six pairs of donor:acceptor blends,including both fullerene derivative and non-fullerene small molecules as the acceptors whose results agree well with that obtained from the PBDB-T:IT-4F-based OSC but not work well with the fullerene-acceptor based devices.Overall,the method presented in this work paves a new pathway to reduce Eloss in non-fullerene OSCs,which offers more opportunities to develop the OSCs with higher PCEs.