Impact investment funds investing in off-market debt instruments are growing in popularity, according to new research.

Research by Phenix Capital shows that impact-focused private debt funds that are currently seeking investment are looking to raise €32 billion ($34 billion) — more than is being targeted by public equity and public debt impact funds combined.

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

The report also mapped private debt impact portfolios onto the UN Sustainable Development Goals (SDGs), finding that SDG 1 — No Poverty — was the most popular theme. Of the funds that had already closed, portfolios worth a combined €24 billion included investments in financial inclusion or poverty reduction projects or companies. A further €17 billion worth of funds are currently fundraising for this aim.

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

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

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

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