Research On Carrier Dynamics And Energy Loss In High Efficiency Ternary Organic Photovoltaic Cells

Organic solar cells have received extensive attention from academia and industry due to their semitransparency,light weight,flexibility,and solution preparation.Among the strategies to enhance power conversion efficiency（PCE）of devices,the ternary strategy not only keeps the simple fabrication process of single-junction devices,but also can partially or simultaneously improve the photovoltaic parameters related to PCE.After introducing third component,attributed to the change of the interfacial electronic structure and the fine-tuning of the morphology in active layer,ternary device often exhibits more complex carrier dynamics,and the related exciton diffusion,dissociation and charge transport,recombination usually involve multiple time scales,which play a vital role for elevating the device performances.In addition,organic solar cells generally suffer from huge energy loss,especially non-radiative recombination loss,which further limit the improvement of device performances.In this article,our research focuses on evaluating carrier dynamics and energy loss in ternary organic solar cells.Through material property analysis and device performance characterization,the role of third component in ternary system is revealed,and the reasons for improved photovoltaic parameters in device and the corresponding physical mechanisms are further demonstrated.The main research contents are as follows:（1）We introduce the small molecule donor DRTB-T-C4 into the PM6:Y6 system,and fabricate a ternary PM6:DRTB-T-C4:Y6 organic solar cell with a PCE of 17.05%.Compared to the PM6:Y6 device,the elevated PCE in ternary device mainly originates from the improved fill factor（FF）.The carrier dynamics analyses show that introducing DRTB-T-C4 effectively promotes the exciton diffusion and dissociation rates,and suppress the charge recombination,contributing for higher FF in ternary device.At the same time,we combine theoretical calculations to analyze the variation of FF in the device.On the one hand,the ternary device exhibits the lowest charge recombination-extraction competition relationship parameter,corresponding to the highest FF.On the other hand,the theoretical maximum FF（80.57%）inferred from the equivalent circuit model is close to the measured FF（80.88%）in device.In addition,introducing DRTB-T-C4 effectively reduce the disorder in ternary active layer,suppressing the non-radiative recombination loss in device.This work provides insights for realizing high FF and low energy loss ternary organic solar cells.（2）We introduce the small molecule acceptor ITIC-M into the PM6:Y6 system to construct ternary organic solar cells.Compared with PM6:Y6 device,the optimal ternary PM6:ITIC-M:Y6 device achieves 18.13%PCE,with the simultaneous improvements in short-circuit current(J_sc),open-circuit voltage(V_oc)and FF.After introducing ITIC-M,the ternary heterojunction not only exhibits complementary light absorption,which effectively increases the photocurrent,but also exhibits the matched interfacial electronic structures,which promotes exciton separation and charge transport at the interface.At the same time,a series of analysis methods show that the optimal ternary system exhibits improved carrier dynamics,suppressed non-radiative recombination loss and optimized morphology features after introducing ITIC-M,which effectively improve the device performances.Except for improved photovoltaic parameters,the optimal ternary system also exhibits more excellent stability in device performances.This work demonstrates the importance of simultaneously improving J_sc,V_oc and FF to achieve highly efficient ternary organic solar cells.