Enhanced optical absorbance of epitaxial emitter silicon solar cells with a back germanium epilayer

• Published in: 2011 37th IEEE Photovoltaic Specialists Conference pp. 003022 - 003025
• Main Authors: Lai, D., Yew Heng Tan, Chuan Seng Tan
• Format: Conference Proceeding
• Language: English
• Published: IEEE 01-06-2011
• Subjects: Absorption; Epitaxial growth; Metals; Photovoltaic cells; Silicon; Substrates
• ISBN: 9781424499663; 1424499666
• ISSN: 0160-8371
• DOI: 10.1109/PVSC.2011.6186581

Direct germanium (Ge) epilayer growth on silicon (Si) solar cells offers the potential of improving the power conversion efficiency (PCE) as a result of enhancement in optical absorbance, particularly at longer wavelength. The realization of this potential depends critically on the competing effects between the short circuit current density (J SC ) gain due to the improved infrared absorption and the reduction in open circuit voltage (V OC ) due to smaller bandgap in the Ge layer, as well as imperfection at the Ge - Si interface. This paper investigates the feasibility of growing a thin Ge epilayer, by rapid thermal chemical vapor deposition (RTCVD), on the backside of a Si solar cell with epitaxial emitter. Experimental results of the solar cell with such configuration yield a remarkably high J SC of 35.1 mA/cm 2 , V OC of 445 mV, and a respectable PCE of 4.6% under one sun and AM 1.5G illumination with no surface texturization or antireflective coating. A high fill factor (FF) could be realized in the cell with further optimization in surface passivation, contact resistance and reduction of misfit dislocations at the Ge - Si interface.