Research On The Mechanism Of Photo-induced Degradation And Device Stability Of Polymer Solar Cells

Polymer solar cells are solid thin film devices that directly convert light energyinto electrical energy, and bear the advantages of low production cost, light weight, andflexible preparation. Therefore researchers from both academes and related industrieshave showed much interest in them in recent years. But their stabilities have been stillweak. In this paper, we study the mechanism of photo-induced degradation and devicestability of polymer solar cells. The main research content is as following:Firstly, the effects of hinder amine TMP on the stability of the active layer of thepolymer solar cells are studied. There are two active layer materials in this study, P3HTand MEH-PPV respectively. Active layer thin film with and without added hinder amineTMP are together put under the irradiation of UV-O3in order to accelerate photo-induced degradation of the conjugated polymer. After degradation the molecularstructure and absorption of visible light of polymer are tested by IR spectra andultraviolet visible spectrophotometer, respectively. Analysis of the mechanism of photo-induced degradation and experiment results of degradation is also investigated. IRspectra shows that the destruction of the molecular structure of polymer added hinderamine is relatively little to a certain extent, hinder amine can suppress the destruction ofthe conjugated structure and improve the structural stability of the material. UV-visibleabsorption shows that the decline’s degree of the visible light absorption of polymerdoped with hinder amine is much smaller than undoped polymer. It is possible tomaintain the polymer regioregularity to some extent. These results show that adding asmall amount of hinder amine into the conjugated polymer film can inhibite thedevelopment of photo-induced degradation to some extent, and improve the stability ofthe conjugated polymer.Secondly, the effects of hinder amine material TMP on the stabilities of the devicesare investigated. There are two active layer materials used in polymer solar cells andthey are respectively P3HT: PCBM and MEH-PPV: PCBM. The device used P3HT:PCBM as active layer is firstly introduced. The electrode is deposited after theillumination of active layer under UV for about1h, the PCE of the device without TMPdoping decreases by46%, while the PCE of the device with TMP doping decreases by39%. On the condition of5min of the UV irradiation time, the PCE of the devicewithout TMP doping decreases by17%, while the PCE of the device with TMP dopingdecreases only by12%. After testing the devices they are placed into the dryer for6h,the PCE for the undoped device decreases by46%, while that for the doped device onlydecreases by27%. These results indicate that TMP have some antioxidation effect. Afterthe devices being placed into the dryer for24h, undoped antioxidant device efficiency drops87%, while the TMP doping devices decreases only about63%. After the devicesbeing placed in the air for3h, the energy conversion efficiency of devices are alldeclines seriously, undoped antioxidant device’s efficiency drops90%, while the TMPdoping devices decreases about72%. The study also sets the experiment of using MEH-PPV: PCBM as the active layer of the devices. The results are consistent with P3HT:PCBM cells. These results of devices used two different active layers show that thehinder amine material can help improve the device stability of polymer solar cells in acertain extent.