CuInSe₂ nanotube arrays for efficient solar energy conversion

Highly uniform and vertically aligned p-type CuInSe₂ (CISe) nanotube arrays were fabricated through a unique protocol, incorporating confined electrodeposition on lithographically patterned nanoelectrodes. This protocol can be readily adapted to fabricate nanotube arrays of other photoabsorber and functional materials with precisely controllable design parameters. Ternary CISe nanotube arrays were electrodeposited congruently from a single electrolytic bath and the resulting nanotube arrays were studied through powder X-ray diffraction as well as elemental analysis which revealed compositional purity. Detailed photoelectrochemical (PEC) characterizations in a liquid junction cell were also carried out to investigate the photoconversion efficiency. It was observed that the tubular geometry had a strong influence on the photocurrent response and a 29.9% improvement of the photoconversion efficiency was observed with the nanotube array compared to a thin film geometry fabricated by the same process. More interestingly such enhancement in photoconversion efficiency was obtained when the electrode coverage with the nanotube arrays as photoactive material was only a fraction (~10%) of that for the thin film device. Apart from enhancement in photoconversion efficiency, this versatile technique provides ample opportunities to study novel photovoltaic materials and device design architectures where structural parameters play a key role such as resonant light trapping.