The android built-in TTS engine is Pico TTS engine.
You can download and install Google Text-to-Speech Engine. The voice is better.
This is the Google TTS engine:
After you install Google TTS engine, please change the default TTS engine in the Setting:
How to change the default TTS engine:
Settings > Voice input & output > Text-to-speech settings > Default Engine
This app is full functional free but with Ads. You can get the Ads free version in the following link:
The iOS version of this app is as following: