The Performance Optimization Of Bulk Heterojunction Polymer Solar Cells

In recent years, more and more scientists have focused on the research of polymer solarcells, a great amount of polymer materials have been designed and synthesized, leading to ayearly growing of the reported power conversion efficiency. However, improving theefficiency of polymer solar cells is a systematic project, which needs a concerted effort onchemistry, materials science, physics and engineering; it contains not only the design andsynthesis of new compounds, but also the controlling and analysis of the film morphology,the exploration of device works mechanism, and the proposing of device structure. Thisdissertation focuses on the aspects of the device active layer, hole transport layer and devicestructures, aims to explore the conditions in improving device performance and the reasonsof enhanced performance, the main results are as follows:(1) With PTG1as the donor, we prepared a bulk heterojunction (BHJ) polymer solarcell device with structure of ITO/PEDOT:PSS/PTG1:PC60BM/LiF/Al. Then we researchedthe effect that1,8-diiodooctane of different content added to the blended solution in thepreparation of active layer on the device performance. Furthermore, we further studied onthe device of optimal performance with annealing condition, and found the device possessesthe best performance in the condition of1%addition of1,8-diiodooctane by annealing20min in150oC, the power conversion efficiency is enhanced from4.65%to5.42%. We usedAFM to observe the active layer and found that with the1%addition of1,8-diiodooctane,the active layer has microphase separation with appropriate size, a clear two-phase interfaceis conducive to the carrier separation, while more addition of1,8–diiodooctance will blur thephase interface, which is bad to the carrier separation.(2) With P3HT: PC60BM system as the active layer of the device, we prepared thepolymer solar cell devices with the hole transport layer of MoO3and PEDOT: PSS. After theoptimization of the thickness of hole transport layer in the two kinds of devices, we foundthe devices using20nm MoO3as hole transport layer have better photovoltaic performancesthan those with PEDOT: PSS. Thereinto, Rshis enhanced by20%, Rsis decreased by about10%, PCE is increased from2.57%to3.15%, and FF is increased from0.52to0.63.Meanwhile, the experiment showed that, compared with PEDOT: PSS, the devices usingMoO3also have better stability, they still have definite photovoltaic characteristics afterexposed to air for50h. Applying MoO3to the systems of several other materials and foundthe device performances also have varying degrees of improvement, indicating MoO3as asuperior alternative to the hole transport material PEDOT: PSS has certain promotional value.(3) With PBDT-TID and P3HT as electronic donors, PC60BM as acceptor, and TIPD aselectronic transport material, two batches of inverted polymer solar cell devices werefabricated with high photovoltaic performance. Devices based on PBDT-TID achieved apower conversion efficiency of6.93%, which is50%higher than that of conversionaldevices. It was found that a significant increase in short-circuit current density is the mainreason for the increased PCE, this dissertation analyzes the reason of the increasedshort-circuit current in terms of IPCE spectrum, the light intensity distribution inside thedevice and the vertical phase separation of active layer, and also researches the stability ofthe devices.