Design And Properties Of Organic Small Molecule Donors With Triphenylamine-Diketopyrrolopyrrole As Skeleton

As a new type of solar cells,organic solar cells show great practical value in the field of new energy because of its advantages of lightness,wearability,flexible nature and strong designability.Among them,the device of active layer that matches the fullerene acceptor with small molecule donor is a kind of method exploiting solar energy.Compared with polymer donor materials,small molecule donor materials have advantages of certain molecular weight,easy modification,simple separation and purification,thus becoming a hot spot in the research field of organic photovoltaic materials.Herein,end group modified strategy and conjugate skeleton extension strategy are used to design and synthesize two series of small molecules,and UV-Vis absorption spectrum,cyclic voltammetry properties focusing on the materials are simply summarized,then the related devices are constructred employing PC₆₁BM/PC₇₁BM blended with target molecules to disscuss their photovoltaic properties preliminarily.Detailed introduction is as follows:（1）Triphenylamine-diketopyrrolopyrrole（TPA-DPP）as basic framework,end groups with different electron-withdrawing abilities such as fluorene（FLU）,carbazole（CZ）,phenothiazine（PTZ）,benzotriazole（BTA）and benzothiadiazole（BT）are introduced,then five asymmetric donor materials,namely TPADPPFLU,TPADPPCZ,TPADPPPTZ,TPADPPBTA and TPADPPBT,were constructed.Photovoltaic property test shows that the enhancement of the electron-withdrawing capability attached to the terminal group is beneficial to the improvement of photoelectric conversion efficiency（PCE）,which is attributed to the enhancement of intramolecular charge transfer effect（ICT）.Therefore,the devices of the TPADPPBT/PC₆₁BM based obtained the PCE of 4.27%.（2）The TPA-DPP backbone was extended by employing conjugated backbone extension strategy on the basis of the D-A-D’molecules of TPADPPCZ,TPADPPPTZ and TPADPPFLU,thus three symmetrical long molecules,namely DTPADPPCZ,DTPADPPPTZ and DTPADPPPh FLU were obtained.In this way,the effect of skeleton extension on the optoelectronic properties of the molecule was explored.The results show that the light absorption range of the material is broadened and the band gap is narrowed,the molar extinction coefficient is nearly doubled,and the carrier mobility and charge transport balance of devices based on its material are significantly improved,especially the device of DTPADPPPh FLU/PC₇₁BM obtained a higher efficiency of 7.44%and a higher voltage of0.94 V,which is attributed to the deeper HOMO level originated from the weak electron-donating ability of FLU,besides,the more balanced charge mobility improve J_SC(19.71 m A cm^-2),in the same time,PCEs were improved.In summary,eight novel small molecule donor materials were designed and synthesized by using two strategies,which adjusted the photovoltaic properties of the materials to some extent.In particular,DTPADPPCZ,DTPADPPPTZ and DTPADPPPh FLU,three symmetric long molecules,have good optical absorption and narrow band gap with high conjugated degree.Moreover,optimal photovoltaic performance was obtained.Therefore,it is an effective means for developing effective organic photovoltaic materials to construct novel small molecule donor materials employing the combination of triphenylamine and diketopyrrolopyrrole.