Cause a voltage drop of about 1V
You are in need of a voltage regulator.
A diode drop is not ideal (no pun intended). It's only 0.7V for a certain current for a certain diode make for a specific diode. i.e. Given several diodes, they will all measure a little different.
I would suggest adding another battery in series, then use a buck regulator to turn it into the low voltage (5V or 3.3V) that you need.  Buck regulators are very efficient nowadays and can commonly be found in the upper 80%.
If you don't need 5V, then you can skip the extra battery.