Effect Of Alkyl-thiol Additives On Polymer/non-fullerene Solar Cells

Polymer solar cells have attracted much attention due to their simple preparation process,low cost and light weight.However,compared with inorganic solar cells,the device efficiency is still far from satisfactory.As a simple and efficient method to improve device efficiency,additives are widely used in fullerene-based solar cells.In non-fullerene systems,the effect of solvent additives on molecular stacking may be different from that of fullerene systems,but the mechanism of action of additives in non-fullerene systems is not clear and perfect.In this paper,three alkyl-thiol additives 1,3-propanedithiol(PDT),1,4-butanedithiol(BDT),1,8-octandithiol(ODT),were applied to solar cells based on polymer/non-fullerene system.The effect of these additives on the performance of devices and the mechanism in non-fullerene system were studied by means of analyzing morphology,absorption spectra and photoluminescence spectra of active layer films.The main work and innovations of this paper can be summarized as follows:Inverted bulk-heterojunction polymer/non-fullerene solar cells based on PBDB-T:ITIC system were prepared,and the preparation conditions of active layer were optimized to improve device efficiency.Firstly,the spin-coating speed of the active layer was changed to confirm the optimum film thickness.Then,the device efficiency is increased to 8.13%through a series of experiments at different annealing temperatures/time.After that,the ratio of the classical solvent additive 1,8-diiodooctane(DIO)was optimized in the PBDB-T:ITIC blend solution.Finally,the PCE of the device was increased to 8.58%under the condition of adding 0.5%DIO.Three alkyl-thiol additives PDT,BDT and ODT were added into PBDB-T:ITIC blend to prepare BHJ solar cells and PDT and BDT were first used as additives in polymer/non-fullerene systems.It is found that the short-circuit current Jsc and filling factor FF of the photovoltaics devices can be maximized at the ratio of 1%,0.5%,0.5%for PDT,BDT,ODT,and the efficiency of the device increased to 9.04%,9.33%and 9.44%,respectively.Compared with the basic devices without additives,the efficiency of the devices increased by 13.7%,14.8%and 16.1%,respectively.Through the analysis of the morphology of the active layer,it is found that three additives can improve the crystallinity of the films and the phase separation of materials in active layer.The size and distribution of the grains became more uniform as well,and at the same time,the coherence length of ITIC crystalline domain increased to varying degrees,which means that the order of ITIC crystalline phase is improved,but the effect on donor PBDB-T is not obvious.Such a change will be more conducive to the transmission of electrons and a better balance between the transport of holes and electrons.