There is a community built image for it here: LEDE 17.01.6 complete custom build for TP-LINK WR941N(D) WR841N(D) WR743N(D) WR741N(D) WR740N(D) All Versions
Or you can build your own using https://openwrt.org/docs/guide-user/additional-software/saving-space and one of the guides. There is also a community built online builder: Online ImageBuilder and Upgrade Server