Investopedia page on microfinance: https://www.investopedia.com/terms/m/microfinance.asp

For articles on microfinance; search EconLit and ProQuest One Business.

For books on microfinance search Library Catalog using microfinance as a Subject Word.

Take a look at The Microfinance Gateway.

CGAP, The World Bank microfinance site, has a data section.

The International Labour Organization has a resource guide on microfinance.