rectifier efficiency

In over simplified terms, the junction stores charge carriers. It takes a while for them to fill up and provide a low resistance path when the junction is forward biased, and a while for them to be pulled out of the junction before it acts like an insulator when reverse biased. The higher the frequency, the bigger part of each cycle these transient processes take.

Thank you for your response.

Just from what you mentioned, it seems that while this junction moves from the condition of a forward-biased to a reverse-biased, at higher frequency, it always causes some delay. Right? And this delay is the cause of the low conversion efficiency in low-frequency rectifier. Then, should there be a high frequency rectifier attaining some better efficiency in terms of conversion efficiency?

Besides, while considering power dissipation across the diodes, at high frequencies, the power efficiency between IN and OUT is a great variation. I wonder if this is only a matter of matching.

There are several rectifier technologies that have different frequency-efficiency relationships. There are PN junction diodes made with various semiconductor materials and with process variations (doping, grading, additional elements added to alter the lifetimes charge carrier pairs, etc) to optimize various properties and compromise others. There are also Schottky half junction diodes that involve a metal, semiconductor junction. Conduction in these materials does not involve positive charge carriers in the metal half of the junction, only electrons. This type is very fast at switching from conducting to insulating, but have high junction capacitance that passes some current in the reverse biased direction. They also have much lower reverse break down voltages than PN junctions made with the same semiconductor material. but also about half of the forward biased voltage drop. When made with a very high band gap semiconductor, they can achieve hundreds of volts reverse capability.

Not sure what your point is. The difference between power in and power out should be the power dissipated by the diode.

Finding the best technology and device type for a given application is a big part of the design problem. Keeping up with the technological advances and production availability is an ongoing task.