Electron Transport Materials And Ternary Bulk Heterojunction Structure Investigations Of Polymer Solar Cells

Polymer solar cells devices（PSC） have attached wide attention for their easy fabrication, low cost, and potential flexibility. It is one of the most promising photovoltaic devices in recent years. Much attention has been focused on how to design the donor materials with higher absorption in a broader wavelength and how to tune the Highest Occupied Materials Orbital（HOMO） and Lowest Unoccupied Materials Orbital（LUMO） energy for an ideal band- gap. Additionally, some groups concentrate on the buffer layer. However, very few attention has been paid to the PSC’s structure, leading to simple device structures. In this thesis, we have dedicated much efforts on the optimization of standard PSC devices. And device performance has been significantly improved attained by introduinge the new functional materials such as electron transport material and the third donor material into the device structure..Firstly, considerable efforts have been taken to the fabrication of standard PSC devices based on the Poly（3-hexylthiophene-2,5-diyl）（P3HT） and the Poly[[4,8-bis[（2-ethylhexyl）oxy]benzo[1,2-b:4, 5-b’]dithiophene-2,6-diyl][3-Fluoro-2-[（2-ethylhexyl）carbonyl]thieno[3,4-b]thiophenediyl]]（PTB7） donor material respectively. And then the device performance has been remarkably enhanced by the technical optimizations, such as annealing conditions, utilization of additives, and the solutions. Finally, relatively high power conversion efficiency（PCE） of 3.32% and 7.6% have been achieved for the devices based on P3 HT and PTB7, respectively.Secondly, we have studied the effects of electron transport materials（ETM） on the PSC device performance. We note that the relatively high HOMO Energy of ETM layer would prevent the holes reaching cathode, which would severely decrease the carriers transporting properties. Herein, we have demonstrated that device performance can be significantly enhanced by improving the electronic carrier mobility of ETM through the investigation of various ETMs such as Tm Py Pb, TPBi,Alq3 and BCP.. High PCE of 3.76%, V_oc of 0.634 V, and Jsc of 9.91 m A/cm² have been obtained by utilization of the highly efficient electron transporting material, Tm Py Pb. Moreover, we have studied the stability of the device incorporated with the ETM. And the device exhibited high stability withthe PCE of 2.38%, V_oc of 0.616 V even after 300 min indicating that the device stability can be significantly enhanced by the utilization of Tm Py Pb as electron transporting layer while keeping high PCE.Finally, we have done some research on the ternary bulk heterojunction as the active layer, namely, P3HT:PTB7:PC₆₀BM acting as the active layer. In this section, we firstly redulated the ratios of the two donors from 1:0 to 0.7:0.3. And we have found out that the band-gap（⁰.1 e V） between the HOMO of P3 HT and PTB7 would seriously prevent the hole transporting into P3 HT layer, decreasing the current density. Finally, the optimal ratio of 0.9:0.1:0.7 in o-dichlorobenzene has been obtained, with which the the PC E of the corresponding device reached 3.83% with the V_oc of 0.66 V.