Morphology Control Of Active Layer In All Polymer Solar Cells

All-polymer solar cells(all-PSCs)use a blend of polymer donors and polymer acceptors as the active layer,which have outstanding advantages of excellent stability and good mechanical properties,and have broad application prospects in the field of flexible photovoltaics.The difficulty in developing high-performance all-PSCs lies in the control of the blended phase separation morphology of the polymer donor and polymer acceptor in the active layer,and its blended phase separation morphology often has the problems of large phase domain size and low phase domain purity.Commonly used blending phase separation morphology controlling methods,such as thermal annealing,solvent annealing,and solvent vapor annealing,have very limited effects in all-PSCs,and cannot achieve substantial improvements in the photovoltaic performance of the device.Therefore,there is an urgent need to develop some methods suitable for phase separation morphology control of the active layer of all-PSCs based on the characteristics of the polymer itself.In response to the aforementioned problems,based on the slow diffusion of polymers in solution,the use of boron-nitrogen coordination bond polymer acceptor materials,this paper has proposed the core strategy of "controlling the active layer morphology of all-PSCs by controlling the pre-aggregation of polymer donors/acceptors in solution".By changing the solution preparation method,controlling the temperature of the solution,and optimizing the molecular weight of the polymer,the regulation of the phase separation morphology of the polymer donor/polymer acceptor and the improvement of the performance of the all-PSCs devices are realized.On this basis,through the use of high-efficiency polymer acceptor materials,an all-PSC device with a power conversion efficiency of more than 15%has been developed.The details are as follows:1.The influence of the way of dissolving the polymer donor/acceptor separately to prepare the solution on the phase separation morphologyThe polymer donor/acceptor solution used to prepare the active layer by spin coating,and the traditional preparation method is to dissolve the two polymers together,resulting in a low degree of phase separation of the two polymers during the film formation process,which is not conducive to the improvement of the efficiency of all-PSCs.In response to this problem,based on the polymer donor J61 and the polymer acceptor PBN-10,we take advantage of the self-aggregation and slow diffusion of polymer chains in the solution,by dissolving the polymer donor and polymer acceptor separately,then blending to prepare the solution,and immediately spin coating to prepare the active layer,the crystallinity of the polymer in the active layer is improved,the phase separation size is increased,and the phase domain purity is improved.Therefore,the short-circuit current and fill factor of the device are improved.The power conversion efficiency of the device using the traditional solution preparation method of dissolving together is 5.36%,while the power conversion efficiency of the device using the solution preparation method of dissolving separately is increased to 7.09%.2.Control the temperature of the polymer solution to increase the crystallinity and reduce the phase domain sizeThe polymer donor/acceptor forms self-aggregation in the solution,and the degree of aggregation is temperature-dependent.Therefore,we propose controlling the phase separation morphology of the active layer of all-PSCs by controlling the temperature of the polymer donor/acceptor solution.Based on the polymer donor CD 1 and the polymer acceptor PBN-12,the research results show that as the solution temperature increases,the crystallinity of the polymer in the active layer first increases and then decreases,and the phase separation size first decreases and then increases.When the polymer solution temperature is 90?,the active layer exhibits the smallest phase domain size and excellent crystallinity,achieving the highest power conversion efficiency.Under this optimized temperature,the power conversion efficiency of the all-PSC reaches 10.1%,which is higher than the device efficiency obtained at room temperature.3.The influence of molecular weight of polymer donor/acceptor on phase separation morphologyWe selected the polymer donor CD1 with number average molecular weights of 14.0,35.5,and 56.1 kg mol-1 and the polymer acceptor PBN-14 with number average molecular weights of 32.7,72.4 and 103.4 kg mol-1,and systematically studied the influence of the molecular weight of the polymer donor and polymer acceptor on the phase separation morphology and device performance of all-PSCs.The research results show that the higher the molecular weight of the polymer material,the stronger its aggregation in the solution;when one of the polymer donors/acceptors has a higher molecular weight,the blend morphology shows obvious bicontinuous fibers network structure;As the molecular weight of the polymer donor or acceptor increases,the influence of the molecular weight of the polymer donor or polymer acceptor on the performance of the device gradually weakens;When the molecular weights of the polymer donor CD1 and the polymer acceptor PBN-12 are both moderately 35.5 kg mol-1 and 72.4 kg mol-1,they show a better blended phase separation morphology and obtain the highest device performance,PCE reached 10.1%.4.Develop high-efficiency all-polymer solar cells by controlling the aggregation state of polymers in solutionBased on the polymer acceptor PBN-25 containing boron-nitrogen coordination bond developed by the research group,it was matched with the polymer donor PM6,by adjusting the preparation method of the polymer solution,the aging time of the polymer solution and the heating time of the polymer solution,the aggregation state of PM6 and PBN-25 in the solution is finely controlled,and finally developed an all-PSC with a PCE of more than 15%.