  It is found that if the inert conductor P has a larger electron work function
$\phi$ and surface state function G than the inert conductor N, the inert
conductor P and the inert conductor N are isolated by a separator and then
immersed in the solution S (abbreviation: inert
conductorP$\mid$solutionS$\mid$inert conductorN, or as P$\mid$S$\mid$N).
Excluding the electrochemical reaction and thermoelectric effect of
P$\mid$S$\mid$N, etc., it is measured that the voltage between the two
conductors after the open circuit continues to increase to a certain stable
maximum value. Then, the current after the closed-circuit continues to decrease
to a certain stable minimum value. Analysis of the structure and properties of
P$\mid$S$\mid$N shows that the inert conductor/solution interface relies on
physical adsorption to construct van der Waals heterojunctions and that two van
der Waals heterojunctions of different potentials form a P-N junction for
P$\mid$S$\mid$N. The inert conductors P and N have different potentials. This
electric field energy is expressed in the outer circuit when the circuit is
open, due to the joint action of the electron work function $\phi$ and the
surface state function G, P$\mid$S$\mid$N generates a larger built-in electric
field and obtains a larger voltage. When the circuit is closed, P$\mid$S$\mid$N
only has the effect of the surface state function G, which produces a smaller
built-in electric field, results in a smaller voltage and current. This
Thermoelectric conversion phenomenon is called the thermovoltaic effect.
