Extracted from the chloroplasts of green plants, Photosystem I (PSI) is a multi-subunit protein complex that can be deposited as a thin film onto electrodes and incorporated into biohybrid photovoltaic devices to convert sunlight into usable energy. Previously, our group characterized persistent photocurrents over nine months using PSI multilayer films in an aqueous solution of redox mediators. However, the loss of periphery PSI proteins upon exposure to mediator solutions is known to affect the photocatalytic performance of the overall film. The cross-linker 2-iminothiolane (2IT) is capable of connecting protein molecules with covalent bonds, and is herein used to stabilize PSI multilayer films on gold substrates against significant desorption/degradation. Results showed that the thickness retainment of the cross linked PSI films was superior to that of non-cross-linked films. PSI films modified by 21T maintained production of photocurrent with long-term exposure to aqueous solutions in contrast to non-cross linked control films. (C) 2016 Elsevier Ltd. All rights reserved.