Micro-nano Composite Structure Induced Multiple Mechanisms To Improve The Performance Of Organic Solar Cells

Organic solar cells(OSCs)have the advantages of flexibility,light weight,environmental friendliness and large area preparation.They are the most promising next-generation batteries.However,its low power conversion efficiency and short life limit its commercial application.The main factor affecting power conversion efficiency is the mutual restriction between the thickness of the active layer and the short exciton diffusion length.Therefore,how to improve the light absorption without increasing the thickness of the active layer has become the focus of the research.The researchers improved the performance by introducing micro or nano structures of different shapes and sizes into the OSCs.In this paper,micro-nano composite grating(MNCGs)structures were prepared,and the mechanism of enhanced OSCs light absorption was analyzed by using the rigorous coupled wave analysis(RCWA)and finite-difference time domain(FDTD)systems.The research work of this paper mainly includes the following aspects.1.Preparation of micro-nano composite periodic grating.Firstly,we use the ultraviolet photolithography to fabricate an one-dimensional rectangular grating(p =6?m).Secondly,we use the two-beam laser interference lithography to prepare the nano-period grating structure.By adjusting the incident light angle and controlling the grating period,we can obtain the nanoscale structure with the period of 250 nm.Finally,the MNCGs structure was prepared by combining the two processes.2.Analysis of OSCs light absorption mechanism of micro-nano composite periodic grating structure.We embedded MNCGs at the interface between the active layer and Ag cathode in OSCs,and the RCWA numerical calculation methods are used to investigate the absorption-enhancement mechanisms.Studies have shown that the multiple mechanisms of MNCGs(plasma-microcavity resonance,double microcavity resonance,scattering)can further enhance the light absorption of active layer compared with the single structure.Finally,the theoretical calculation of FDTD shows that when the OSCs active layer materials are PTB7:PC71BM and P3HT:PCBM respectively,compared with the planar OSCs with the same active layer materials,the optical absorption of the active layer materials in the intrinsic absorption band is significantly enhanced,and it is enhanced by 57.41% and 20.43% at 700 nm and 525 nm respective.3.Preparation and optimization of bimetallic electrode OSCsBecause ITO has low resistance and high light transmittance,it is often used as an electrode for OSCs.However,brittle ITO is difficult to satisfy the needs of flexible devices.The inert electrode(Ag,Au,etc.)has good conductivity and stability,and is suitable for flexible devices.We prepared bimetallic electrode OSCs using Ag instead of ITO and optimized the thickness and active layer solution concentration of Ag electrode.Finally,when the thickness of Ag is 10 nm and the solution concentration is 20 mg/ml,the best performance of the device PCE reaches 2.16%,which is comparable to the efficiency of ITO devices(2.91%).