Proven theories from other disciplines are often helpful to give solid grounding in multidisciplinary research. Did not see much of it in Green IT. I am just starting though.
This is a very broad question. I guess it depends on the specific subject area of study. I mean some studies are based on case studies, some are methodological recommendations whereas other contributions are more theoretical based. It really depends on what you are trying to achieve here.
Green IT basically refers to the effective and efficient use of IT resources with minimal impact on environment in its complete life cycle. so much academic studies can be conducted in green IT adoptions, strategies, product compatibility with existing infrastructure. All these are interdisciplinary studies. If you want to study marketing studies go for cost-benefit analysis as most of the people are not aware of these products and they perceive them to be high price.
I have conducted my Ph.d level research on green IT consumerism. I found much research is done in corporate sector, academic research is very less. However it is an emerging topic, so there is lot of scope in green IT if you can explore.