In US currency, coin collectors (numismatists) generally agree that pennies 1943 or earlier have higher value than those minted after. The reason being those minted 1943 or earlier had a higher silver content. It was a fact that copper was highly in demand for making artillery during the war.
The most valuable penny is the 1943 Copper Penny, the estimated value is between $10,000 to a possible $100,00. Most pennies were zinc-coated steel, the nickel and copper were saved for the war. It is believed the making of the 1943 pure Copper Penny was an accident.