Research On Semitransparent Organic Solar Cells Based On Optical Regulation

Organic solar cells have attracted extensive attention of researchers due to their light weight,simple preparation method,good flexibility and good transparency.Semitransparent organic solar cells（STOSCs）are important research direction in organic solar cells.They can be integrated into buildings,which is the biggest advantage.In recent years,due to the emergence of non-fullerene small molecular materials Y6,the power conversion efficiency（PCE）of STOSCs have reached 14%at a high average visible transmittance（AVT）of 20%.In addition to PCE and AVT,color rendering performance is also an important parameter for STOSCs.Generally speaking,in order to meet the requirements of building integrated photovoltaics（BIPV）for the color of transmitted light,STOSCs are required to transmit neutral or colorful light.In the current research,optical regulation methods such as optical regulation layer,photonic crystals and Fabry–Pérot resonator can realize STOSCs to transmit neutral or colorful light.In this paper,Mo O₃is used as the optical regulation layer to realize the high-performance neutral color STOSCs,and WO₃is used as the intermediate dielectric layer of Fabry–Pérot resonator to realize the high-performance colorful STOSCs.The research contents are as follows:1.We chose D18-Cl:Y6:PC₇₁BM ternary system as the active layer of the organic solar cells.By adjusting the thickness of the active layer,16.40%PCE of opaque organic solar cells was realized.On this basis,we used 20 nm Ag as the transparent electrodes of STOSCs.The device achieved 12.08%PCE and 16.90%AVT.However,the AVT value was still lower than 25%,and the color coordinates（0.2768,0.2545）of the device on CIE 1931 chromaticity diagram were located in the blue light region,which will limit the practical application of the device.In order to obtain neutral STOSCs,Mo O₃was used as the optical regulation layer.Using the semitransparent device with 20 nm Mo O₃,the AVT value and color coordinates were significantly increased to 25.45%and（0.2953,0.2822）,respectively,while the PCE was slightly reduced to 11.58%.Finally,we use the transfer matrix method to simulate the optical field distribution of the semitransparent device.The results showed that Mo O₃reduced the optical field intensity in the active layer,which significantly improved the AVT and color rendering performance of the semitransparent device.2.A Fabry–Pérot resonator electrode composed of Ag/WO₃/Ag was designed and measured.The electrode used 30 nm Ag film as the reflecting layer and WO₃as the spacer between the two Ag films.By adjusting the thickness of WO₃,the electrode can selectively transmit photons in a certain wavelength.We calculated the transmittance of WO₃with a thickness of 60,80 and 100 nm and found that it can selectively transmit blue,green and red light and inhibit photons in other wavelength.Subsequently,we prepared Ag/WO₃（60,80 and 100 nm thickness）/Ag electrodes.The peak transmittance of the electrodes to blue,green and red light was as high as25.0,38.3 and 41.3%.We applied the colorful electrodes to the optimized D18-Cl:Y6:PC₇₁BM ternary system.The PCE of blue,green and red devices were 13.78,13.65and 13.54%respectively,and the peak transmittance was greater than 15%.Finally,we simulate the optical field distribution of the colorful semitransparent device.The results show that the optical interference of Ag/WO₃/Ag leads to the optical field intensity at modulation wavelength range in the active layer is lower than that in the electrodes,and with the change of WO₃thickness,the wavelength range of the resonance region in the electrodes can well correspond to the wavelength range of the peak transmittance of the device.This paper reports two optical regulation methods,and realized high-performance neutral color and colorful STOSCs,which can meet the needs of different occasions of BIPV.It has a certain reference significance for the research and development of STOSCs in the future.