Study Of Photomultiplication Type Organic Photodetector With Broadband Spectral Response Range Based On COTIC-4F

For infrared organic photodetectors applied in variable low lightl environments,researchers have found that adding suitable narrow bandgap organic materials in the active layer can broaden the near-infrared spectral response range,improve the film morphology,enhance the response performance,and reduce the dark current.Meanwhile,strategies such as increasing the active layer thickness,adding a third component to form the energy cascade,and exploiting the multiplication effect can also enhance the photovoltaic performance of the devices.In this thesis,a new narrow bandgap non-fullerene receptor COTIC-4F is added into the multiplication system which is P3HT:PC₇₁BM（3:100）,and a small proportion of the donor P3HT acts as a hole trap to trap the photogenerated holes,thereby inducing the multiplicative injection of electrons from the external circuit.The introduction of COTIC-4F can not only reduce the agglomeration of fullerene material PC₇₁BM,but also effectively broaden the near-infrared spectral response range of the device.The effects of four different ratios of active layers on the response performance of broad-spectrum multiplication organic photodetectors are investigated,where the structural composition of the active layers is P3HT:PC₇₁BM:COTIC-4F（3:100-x:x）.It is proved that the ternary active layer prepared with the ratio of 3:60:40 and the film thickness of 500 nm is best.The ternary active layer device can broaden the response spectrum of the binary active layer device from 300～730 nm to 300～1200 nm.The device achieves the highest EQE and the highest D^*of 6204%and 1.70×10¹² Jones at 20 V bias,and the EQE and D^*at 1100 nm reach 742%and 2.59×10¹¹ Jones.Next,in order to improve the low response performance of devices with ternary active layer in the near infrared range of 930～1200 nm,Y6 is added to the optimal ratio of ternary active layer（3:60:40）.Varying the ratio of COTIC-4F and Y6,it is found that3:60:20:20 was the optimal ratio for the quaternary active layer(P3HT:PC₇₁BM:Y6:COTIC-4F).The introduction of Y6 compensated the absorption depression of the ternary active layer at 600～800 nm,which improved the morphology of the active layer,and introduced new P3HT:Y6 hole traps which can improve the multiplicative injection effect.It is noteworthy that the energy cascade structure is formed between the organic materials in the active layer of the device.It is demonstrated that the energy cascade structure can effectively reduce the energy loss of photogenerated charges during the transmission process,especially the energy loss of photogenerated charges generated by COTIC-4F,which effectively enhances the detection capability of the device in the NIR spectral range.The maximum EQE and the maximum D^*of the device reach 21182%and 1.82×10¹³Jones at 20 V bias.When the wavelength of monochromatic light is 1100 nm,the EQE response value and D^*response value of the device are 4013%and 4.49×10¹² Jones,respectively.In summary,this thesis extended the response range from 300 to 730 nm to the 1200nm NIR region by adding the non-fullerene NIR absorbing material（COTIC-4F）to the multiplication system(P3HT:PC₇₁BM).Further,Y6 is added into the ternary active layer device to form a dual-energy cascade structure between not only the HOMO levels but also the LUMO levels of the organic materials in the quaternary active layer,which effectively improves the response performance in the 930～1200 nm near-infrared spectral range.