Photophysical Mechanism Of Organic Solar Cells Based On B?N Materials

Since the 1990 s,the unique advantages of organic solar cells(OSCs)have been widely concerned,including:(1)organic solar cell manufacturing materials can be synthesized in large quantities on a large scale to reduce material costs;(2)organic solar cells can be used in industrial roll-to-roll solution processing for large-scale applications can be prepared,and it can also be produced in large areas on flexible substrates,which can effectively reduce manufacturing costs and achieve the requirements of ultra-light,ultra-thin,bendable,and translucent.However,the photon energy loss was high,about 0.7-1.1e V,resulting in low open-circuit voltage,which theoretically limited the improvement of photoelectric conversion efficiency.The all-polymer solar cell based on a new type of electron acceptor material,a boron-nitrogen polymer,has an energy loss of only 0.51 e V and an open circuit voltage of 1.0-1.1V.This provides a potential for breaking through the efficiency bottleneck of OSCs,but the type of battery has low short-circuit current density and fill factor.In this paper uses time-resolved spectroscopy to study the energy loss mechanism in high opencircuit voltage all-polymer solar cells.It was possible to reveal the photophysical mechanism of high open-circuit voltage all-polymer solar cells and improve its photoelectric performance.The results showed that proper driving force for charge separation and thin film phase separation structure were great significance to reduce photocurrent loss and improved photoelectric performance.The details were as follows:(1)Through the preparation and characterization of PCE10: P-BNBP-T OSCs,the best preparation process for the active layer thin film was determined,and the steady-state and transient spectrum thin-film samples were prepared using the best preparation process.Then,the steady-state and transient spectra of pure PCE10 thin film and pure P-BNBP-T thin film were analyzed,and the lifespan of each particle was determined by exponential fitting of each peak attenuation kinetic process.The steady-state and transient spectra of PCE10: P-BNBPT hybrid films were studied: PCE10 and P-BNBP-T can effectively extend the lifetime of polarons.PCE10: P-BNBP-T The lifetime of the polaron was significantly longer than that of the pure PCE10 film,which was beneficial to the collection of the polaron by the electrode to generate photocurrent.However,the test results of the device's photoelectric performance show that both the generated polaron and the effective polarizer collected by the electrode are less.The weight of the excited state particles returned to the ground state by radiative or non-radiative transitions was still very large,which will cause a large amount of energy loss and cause the degradation of the photoelectric performance.(2)In order to investigate the influence of the charge separation driving force on the photocurrent loss,P-BNBP-FBT,which was different from the LUMO and HOMO energy levels of P-BNBP-T,was used for the photophysical research.Through the preparation and characterization of PCE10: P-BNBP-FBT OSCs,the optimal preparation process of the active layer thin film was determined,and the steady-state and transient spectral thin film samples were prepared using the optimal preparation process.Then,the steady-state and transient spectra of pure P-BNBP-FBT thin film were analyzed.The exponential fitting of each peak decay kinetic process was performed to determine the lifetime of each particle.The steady-state and transient spectra of PCE10: P-BNBP-FBT mixed films were studied: PCE10: P-BNBP-FBT mixed films can effectively improve the lifetime of polarons.The life of PCE10 pure film polaron was greatly extended,which was beneficial for the polaron to be collected by the electrode and generate photocurrent.By comparing the kinetic fit results of the ground state bleaching characteristic peaks and polaron characteristic peaks of the PCE10: P-BNBP-T blended film with the PCE10: P-BNBP-FBT blended film and combining the device efficiency,it was that: The HOMO and LUMO energy level matching of the acceptor material can prolong the lifetime of excited particles,which was conducive to the diffusion and transfer of excitons and the generation and diffusion of polarons,so that the electrode collects more polarons and generates larger Photocurrent,suppress charge recombination,effectively reduce photocurrent loss,and improve device photoelectric performance.(3)In order to investigate the effect of the phase separation scale of the active layer films of OSCs on device performance,two commonly used additives were used: 1-chloronaphthalene(CN),1,8-diiodooctane(DIO)on PCE10 : The phase separation scale of the active layer thin film of P-BNBP-FBT organic solar cell was adjusted.The results showed that DIO could effectively improve the PCE of the device.Then we performed AFM and TEM tests on the blended thin film with DIO,and DIO could reduce the surface roughness and phase separation scale of the small PCE10: P-BNBP-FBT blending film,with the increase of the DIO addition ratio,the surface roughness and phase separation scale continue to increase.The optoelectronic performance of the device was optimal when the DIO addition ratio is 3%.The steady-state and transient spectra of 3% DIO-added mixed films were studied.The steady-state spectra showed that the fluorescence quenching was enhanced after adding DIO to change the phase separation scale of the films.The transient spectra showed that the phase separation scale was appropriate.The polarizer lifetime in the down-mixed film was greatly extended,which is beneficial for the electrode to collect more polarons and generate a larger photocurrent,and reduces the number of excited state particles that release energy through radiative and non-radiative transitions back to the ground state,suppresses charge recombination,reduce the photocurrent loss,and effectively improve the photovoltaic performance of solar cells,respectively.