Study On High Efficiency Organic Solar Cell By Controlling The Morphology Of Active Layer With Additives

Organic Solar Cells（OSCs）have the advantages of simple fabrication process,light weight,low capital consumption,mass production and flexibility,which have attracted a large number of researchers’attention in the scientific community and have made rap id development.In the past three decades,through the design of new semiconductor materials,the development of interface materials,and the optimization of device structures,the power conversion efficiencies（PCEs）of OSCs have exceeded 17%and were approaching the threshold of commercialization.The solvent additive was a simple and effective method to optimize the morphology of the active layer and obtain high-performance PSC.For example,the most traditional additives such as DIO and CN have been successfully utilized to optimize the morphology of various OSCs,but the toxicity that brought by halogen atoms,which limits their corresponding large-scale fabrication,so it is necessary to find green additives.The classical polymer donor material（PTB7-Th）and fullerene derivative acceptor material(PC₇₁BM)were used as the main materials of the active layer,and green,low-toxic,non-toxic additives were employed to modulate the morphology of the active layer of solar cells and to optimize the device performance.By means of current density-voltage（J-V）,external quantum efficiencies（EQE）,atomic force microscopy（AFM）,transmission electron microscopy（TEM）,space charge-limited current（SCLC）,Impedance spectroscopy（IS）,grazing incidence wide-angle X-ray scattering（GIWAXS）,grazing incidence small-angle X-ray scattering（GISAXS）,water contact angle（WCA）,and exciton dissociation,the effects of additives on OSCs were analyzed.The details were as follows.（1）A non-toxic,halogen-free additive ethyl salicylate（EHB）was introduced into the active layer PTB7-Th:PC₇₁BM,and inverted devices with the structure:ITO/Zn O/PTB7-Th:PC₇₁BM/Mo O₃/Ag were prepared to investigate the effect of EHB on the performance of solar cells.It was found that the addition of EHB additive with volume fraction of 2%～7%in the active layer can significantly improve the PCE,where the best device performance was obtained with 5%EHB and the PCE reaches 9.64%.The tested by GIWAXS showed that EHB enhances the ordered molecular stacking of the active layer and improvs the charge transport;GISAXS and WCA test results showed that:Adding 5%EHB active layer on the blend membrane.The top of the surface was PTB7-Th rich area,which was beneficial to exciton disintegration and charge transfer at the interface,and inhibits charge recombination,thus the performance of the device was improved;the results of AFM,TEM and other morphological tests showed that EHB causes better solubilization and rearrangement of the donor and acceptor,resulting in a higher molecular order,which usually appears more crystalline phases and reduces fullerene agglomeration,improving carrier transport and donor-receptor surface contact in the active layer;in addition,SCLC,IS,and exciton dissociation indicated that the additives can promote charge extraction and inhibit charge complexation,thus improving energy conversion efficiency.（2）The green solvent additive methoxymethyl phenyl sulfide（MPS）with different concentrations（0%,1%,3%,5%,7%）was added to the active layer PTB7-Th:PC₇₁BM,and inverted devices with the structure:ITO/Zn O/PTB7-Th:PC₇₁BM/Mo O₃/Ag are prepared to investigate the effect of MPS on the photovoltaic performance of solar cells.The results of AFM and TEM studies showed that MPS makes the roughness value of the active layer surface smaller,reduces fullerene agglomeration,and optimizes the active layer morphology,which was beneficial to charge transport;SCLC and exciton dissociation analysis showed that the photogenerated excitons increase significantly when the additive was added,and at the same time,the charge complex is inhibited,and the exciton dissociation rate was improved,which improves the charge transport,so the final photovoltaic performance was significantly improved;when the concentration of solvent additive MPS was 3%,which efficiency was the best,reaching 9.24%.（3）Different concentrations（0%,0.5%,1%,3%）of the solvent additive methoxymethyl phenyl sulfide（MBZ）,which can be used as a food additive,and added to the active layer PTB7-Th:PC₇₁BM,andinverteddeviceswiththestructure:ITO/Zn O/PTB7-Th:PC₇₁BM/Mo O₃/Ag were prepared to study the effect of MBZ on the solar cell.The effect of MBZ on the photovoltaic performance was investigated;AFM,TEM and other morphological test studies showed that:MBZ makes the donor and acceptor fully soluble and reduces fullerene agglomeration;through the characterization of SCLC and exciton dissociation,the additive has effectively improved the carrier mobility of its photovoltaic devices,which can promote charge extraction and inhibit charge recombination,and the internal migration of the devices is more balanced,so that channels that form a good structure for intercommunication networks,thus improving the energy conversion efficiency.