Impact investment funds that invest in off-market debt securities are growing in popularity, according to a new study.

Research from Phenix Capital shows that impact-focused private debt funds currently seeking investment are looking to raise €32 billion ($34 billion) – more than is targeted by public investment funds and the Combined Public Debt Impact Funds.

Despite the growing popularity of listed green and sustainable bonds, private debt impact funds have raised just over €40 billion to date, more than public debt impact funds.

The report also mapped the impact portfolios of private debt on the United Nations Sustainable Development Goals (SDGs), finding that SDG 1 – No poverty – was the most popular theme. Of the funds already closed, portfolios with a combined value of €24 billion included investments in financial inclusion or poverty reduction projects or ventures. An additional 17 billion euros of funds are currently being collected for this purpose.

Funds targeting sustainable farming and farming – which fall under SDG 2, No Hunger – have between them €17 billion in assets under management.

Other popular themes among private debt impact funds included clean energy (SDG 7) and gender equality (SDG 5), according to research by Phenix Capital.

Of the funds currently in the market seeking new capital, the top five most popular themes were financial inclusion (SDG 1), sustainable agriculture and farming (SDG 2), “gender goal” (SDG 5) and the transition and access to renewable energies (SDG 7).

The research follows findings from Brown Brothers Harriman & Co earlier this year that showed exchange-traded fund investors were increasingly looking to allocate to thematic or impact-oriented products.