What does the research say?
The following articles talk about the benefits of Open Access.
Craig I, Plume A, McVeigh M, Pringle J, Amin M. (2007). Do open access articles have greater citation impact? A critical review of the literature. Journal of Informetrics, 1(3), 239-48. http://www.jstor.org/stable/20510537
Davis, P., Lewenstein, B., Simon, D., Booth, J., & Connolly, M. (2008). Open Access publishing, article downloads, and citations: Randomised controlled trial. BMJ: British Medical Journal, 337(7665), 343-345.
Gargouri Y, Hajjem C, Larivie`re V, Gingras Y, Carr L, et al. (2010) Self-selected or mandated, open access increases citation impact for higher quality research. PLos ONE, 5(10), e13636. doi:10.1371/journal.pone.0013636
SPARC Europe. (2015). The open access citation advantage: Studies until 2015. Retrieved from http://sparceurope.org/what-we-do/open-access/sparc-europe-open-access-resources/open-access-citation-advantage-service-oaca/oaca-list/