If you want to write a PhD thesis, I recommend that you read a number of research papers about the subject, and you may divide the sections according to your university's relevant guidelines. Research papers published in quality journals is better than PhD Thesis since such papers are peer-reviewed and examined fully before publication. The following handbook about the subject may help you out:

Research handbook of finance and sustainability‏

S Boubaker, D Cumming, DK Nguyen - 2018‏ - books.google.com‏

Suggested Topic:

Financial inclusion for poor households

I can only give how-to advice in this specialty, the actual subject should fit your college, its department, and your location, maybe also what want to do after the PhD.

In his classic paper that unveiled his non-parametric ANOVA-like test Friedman (1937) included an example possibly related to your subject area. Maybe his diversity of indexes is a little extreme, but it might give you ideas for studies involving moderate sized samples. However, in your situation I would consider a big data study using PyTourch (https://pytorch.org/). You might look around for suitable huge datasets on the internet. Or ask for suggestions of data sets for download in areas related to household finance and sustainability.

Friedman, Milton 1937. The use of ranks to avoid the assumption of normality implicit in the analysis of variance. J. of the Am. Statistical Association (December 1937) 32 (200):675–701. (Also see errata referring to top p 695: Journal of the American Statistical Association Volume 34, 1939 - Issue 205, p 109)

Sustainable Investing by an Individual Investor

There is a crying need for more research into the impact of poor school (in particular illiteracy and innumeracy) on the use of financial services, and the ability to graduate into formal finance. This is especially problematic when no one in the household can read or write. It also tilts the balance of power strongly in favour of men where women are discriminated against for access to literacy.

Adding to what Brett Mathews writes, the impacts of digital finance including mobile money, savings and micro-insurance is worthy of pursuit under the rubric of 'financial inclusion'. Literature to date is largely focused on supply and emand issues and how to extend digital finance, with a normative assumption that financial inclusion on unbanked segments through mobile phones is beneficial. There is very little research testing how the products are used, what kind of literacy demands are place on households and how they have to continually learn, and lastly whether financial inclusion is actually beneficial or not. As a primer I suggest reading this critical literature review: Kim, M, Zoo, H, Lee, H & Kang, J 2017, 'Mobile, financial inclusion and development: a critical review of academic literature', GlobDev 2017. 4., .

We are trying to look at finances of microentrepreneurs. They are so intertwined with ther family finances that it is impossible to look at the business or the household finances in isolation.

Dear Dimuthu Maduranga Arachchi I agree with Prof-Dr-Ahmed Al-Baidhani أ. د. احمد البيضاني .