With the further development of optoelectronic devices， the trapped optical structure has been widely paid attention to. However， the relationship between inverted pyramid structure， size and its trapped optical performance needs to be studied in depth. Copper-silver co-assisted etching is used to prepare the inverted pyramidal structure and the size of the structure below 1 μm is realized. The study presents that the average size of 1 μm inverted pyramidal structure has the best trapping performance. The inverted pyramidal structure with excellent trapping performance is applied to Si/PEDOT：PSS heterojunction photodetector. The photodetector achieves excellent photoelectric response performance with a 61 mA/W responsivity and 9.20×10¹² Jones specific detectivity for 980 nm wavelength light under an applied 0 V bias. This paper provides a new idea for the preparation of high-performance Si/PEDOT：PSS heterojunction photodetectors and demonstrates that the inverted pyramidal structure has promising applications.