Optimization Of Interconnecting Layers And Optical Simulation For Organic Tandem Solar Cells

Organic tandem solar cells,with higher output voltage and efficiency,have broad application prospects,and thus have received great attention.There are two types of difficulties and challenges in realizing high-efficiency organic tandem solar cells.The first aspect lies in the connection layer connecting the two sub-cells.The ideal connection layer must have high light transmittance,matching energy level with the active layer,and sufficient solvent resistance.The second aspect is the current balance between the front and rear half cells.The current of the tandem cell with the series structure is determined by the smaller current of the sub-cells,and the highest efficiency must be achieved through the current balance of the front and rear junction cells.To solve these problems,this dissertation studies the optimization of the connection layer of organic tandem solar cells and the current balance of front and rear sub-cells.Through experimentation and optical simulations,the high-efficiency organic tandem cells are fabricated.The main research results are summarized as follows:1.Aiming at the incompatibility of the ZnO/MoO_x connection layer,a new connection layer of Zn O/PEI/Mo O_x was developed by introducing a polyethyleneimine(PEI)interlayer for organic tandem solar cells.By introducing the PEI layer,the solvent resistance of the underlying cell has been enhanced and the charge recombination efficiency at the Zn O/Mo O_x interface has been improved.The connection layer is then optimized.The problem of the S-shaped J-V curve of the tandem cells is successfully solved by optimizing the PEI thickness,the optimal thickness is 4 nm.The thicknesses of Zn O and Mo O_x were then optimized to improve the FF of the tandem cell,and the optimal thicknesses were 20 nm and 7 nm,respectively.In addition,based on solution-processed Mo O_x synthesized in the lab,the Mo O_x layer is prepared by spin coating instead of vacuum deposition,and the intermediate connection layer is prepared by the full solution method,with greatly reduced process complexity and preparation time.The PCE of the solution processed device is 15.43%,comparable to device with evaporated Mo Ox layer.2.Aiming at the current balance of the front and rear sub-cells,optical simulation is carried out with the help of FDTD Solution software to guide the optimization of the device structure.Firstly,by simulating the relationship between the thickness of the active layer and the current density of the single-junction cell,and comparing the simulated results with the experimental ones,both have been found having the same trend,which verifies the reliability of the model.The thicknesses of Zn O and Mo O_xwere then simulated,and it was confirmed that the increase of the thickness of these two layers would increase the current of the front half-cell and decrease the current of the back sub-cell,which is consistent with the experimental results.Finally,through the simulation calculation,the relationship between the thickness of the active layer of both sub-cells and the current density was obtained,and the conditions for realizing the current balance were found.Based on the simulation results,and through experimental optimization,the current balance was achieved when the active layer thickness was 84nm and 100 nm for front and back half-cells respectively.The highest PCE of the optimized tandem cell has reached 16.20%.