Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2016)
    Energy Harvesting & Storage Tuesday Sessions
       Session EH-TuM

Paper EH-TuM8
Back Contact Passivation via Atomic Layer Deposition for Increased Device Performance of Earth-Abundant Cu2ZnSn(S,Se)4 Solar Cells

Tuesday, December 13, 2016, 10:20 am, Room Lehua

Session: Surfaces & Interfaces for Solar Cells and Solar Fuels
Presenter: Priscilla Antunez, IBM T.J. Watson Research Center, USA
Authors: P.D. Antunez, IBM T.J. Watson Research Center, USA
D.B. Farmer, IBM T.J. Watson Research Center, USA
D.M. Bishop, IBM T.J. Watson Research Center, USA
R.A. Haight, IBM T.J. Watson Research Center, USA
Correspondent: Click to Email
Thin film solar cell absorbers composed of earth-abundant elements such as Cu2ZnSn(S,Se)4 (CZTSSe) are particularly attractive due to their relative low toxicity and their record maximum power conversion efficiency of 12.6% using an antireflective coating. Despite rapid progress, further improvements in efficiency are needed to enable the commercial-scale implementation of CZTSSe as a solar cell absorber. Our recent efforts have identified the deleterious impact of recombination at the interface between the CZTSSe absorber and the molybdenum back contact, which results in decreased lifetime, compared to the bulk, and a reduced open circuit voltage (Voc), compared to theoretical expectations. To address this limitation, we have employed two approaches designed to increase device performance. The first approach involves the deposition of Al2O3, via ALD, onto the Mo/glass substrate prior to the CZTSSe growth. In the second approach, the CZTSSe device is exfoliated to expose the back surface of the absorber, and a thin Al2O3 layer is then deposited to passivate the back of the solar cell. The passivating ALD step is then followed by the deposition of a high work function back contact. The high work function material further reduces recombination by imposing an electrostatic field, which drives the separation of electrons and holes to increase device performance. These effects are supported by device simulations and confirmed with experimental results that show an increase in several performance parameters, like Voc and Jsc, when high work function back contacts are employed in conjunction with careful control of absorber thickness. With this approach, along with the inclusion of the Al2O3 passivating layer designed to inhibit recombination, efficiencies as high as 11.6% have been achieved without the use of an antireflective coating.