Active Layer Optimization And ZnO Doping For Organic Solar Cells

To meet the challenges of limited global energy supply and environmental pollution,clean and renewable energy has become the direction of research and development in various countries.Organic solar cells can be fabricated on glass substrates or even flexible plastic substrates using solution processing techniques,which have the advantages of low cost,light weight and flexibility,and are currently the focus of research in developing clean energy.However,organic solar cells currently suffer from relatively low energy conversion efficiency and short service life,which limit their commercial application.Therefore,this paper investigates the effects of post-treatment thermal annealing,functional layer additives,and electron transport layer doping on the performance of cell devices with the goal of enhancing the efficiency of organic solar cells as follows:In order to improve the performance of inverted organic solar cells based on PBDB-T:ITIC system,this paper firstly treats the functional layer films of cell devices by post-treatment thermal annealing,and characterizes the performance changes of functional layer films before and after thermal annealing treatment using atomic force microscopy,X-ray diffraction spectroscopy and UV-vis absorption spectroscopy,and prepares the structure of ITO/ZnO/PBDB-T:ITIC/Mo O₃/Ag inverted structure cell devices were prepared,and the effects of annealing on the performance of the cell devices were investigated using the solar cell IV test system and the integrated solar cell QE and photoelectric detection system.It is shown that the thermal annealing operation improves the surface morphology of the functional layer film,effectively improves the orderliness of the arrangement distribution of the donor-acceptor molecules in the vertical space and increases the contact interface of the donor-acceptor molecules;a better interpenetrating network structure is formed,which is more favorable to the carrier transport in the vertical direction of the film.Among them,when the annealing temperature of the film was 150℃,the surface roughness and crystallinity of the film were most obviously enhanced,while the response range of the UV-visible absorption spectrum of the film was the largest and the absorption value reached the highest.In the final device produced,the V_oc of the device obtained after annealing at 150℃for 10 min was 0.870V,J_sc was 16.2 m A/cm²,FF was 63.4%,and the EQE of the device was also increased from52%to 65%,demonstrating that post-treatment thermal annealing can effectively improve the performance of organic solar cell devices.The additive DIO was further introduced into the functional layer solution based on thermal annealing to control the evaporation rate of the solvent and promote the formation of more effective initial film nanomorphology and surface morphology during the spin coating of the solution,increase the contact angle measurement to characterize the effect of additive DIO on the functional layer film,and further characterize the effect of additive DIO on the performance of the cell device using space charge limiting current method and electrochemical impedance spectroscopy.Experimental investigations yielded that the most significant PCE enhancement of 9.05%and FF elevation to 64.17%for the cell device was obtained after adding 2%volume percentage of additive DIO to the functional layer.At the same time,the charge transfer resistance of the device decreased by 9%compared to that without the addition of DIO to about 1820Ω.The carrier migration rate was also significantly enhanced with a value of about 0.97×10^-2 cm²V^-1s^-1.Finally,the ZnO:Mg electron transport layer was prepared by doping the ZnO precursor solution with magnesium acetate tetrahydrate,which achieved better energy level matching between the electron transport layer and the functional layer,reduced the ZnO surface defects,and optimized the contact interface between the functional layer and the ZnO electron transport layer.The PBDB-T:ITIC material system was used as a functional layer material to prepare inverted organic solar cell devices,and the best results were obtained when the doping mass percentage of magnesium acetate tetrahydrate was 2%,with V_oc of 0.874 V,Jsc of 16.9 m A/cm²,FF of 63.1%,and PCE of 9.4%for the devices.The 6%increase in PCE compared to the undoped ZnO device,along with the increased cell device lifetime,makes it commercially viable.