Abstract
A heterostructure of Sn-doped In2O3 (ITO)/Al-doped ZnO (AZO)/n-Si was proposed and studied for photovoltaics. The top ITO worked as a transparent conducting layer for excellent optical transparency and current collection. The AZO/n-Si served as the active junction and provided the built-in potential (qVbi) for the photovoltaic devices. To achieve a higher open circuit voltage (Voc), which is the main challenge for AZO/Si heterojunctions due to the junction interfacial defects, the AZO and AZO/Si junction properties were systematically investigated. By modulating the Al doping in the AZO thin films via a dual beam co-sputtering technique, the AZO/n-Si junction quality was significantly improved with qVbi increased from 0.21 eV to 0.74 eV. As a result, the Voc of our best device was enhanced from 0.14 V to 0.42 V, with a short circuit current (Jsc) of 26.04 mA/cm2 and a conversion efficiency (Eff) of 5.03%. To our best knowledge, this is the highest Voc reported for ZnO/Si heterojunctions prepared by the sputtering method. The results confirmed the validity of our proposed structure and junction engineering approach and provided new insights and opportunities for ZnO/Si heterojunction optoelectronics.
Highlights
ZnO, a transparent conducting oxide (TCO) material with a wide direct bandgap and a high exciton binding energy has been widely studied for various optoelectronic applications such as light emitting diodes (LEDs), laser diodes, photodetectors, and photovaltics [1,2,3,4,5,6,7,8,9]
ITO/Al-doped ZnO (AZO)/n-Si heterostructure was proposed for enhanced photovoltaic applications
It allowed junction engineering by introducing uniform Al doping in AZO with precise control of the doping concentrations
Summary
ZnO, a transparent conducting oxide (TCO) material with a wide direct bandgap and a high exciton binding energy has been widely studied for various optoelectronic applications such as light emitting diodes (LEDs), laser diodes, photodetectors, and photovaltics [1,2,3,4,5,6,7,8,9]. Undoped ZnO has an electron affinity of 4.35 eV and direct bandgap energy of 3.28 eV with ~ 1017 cm−3 of an electron concentration. Transparent heavily Al-doped and Ga-doped ZnO have been demonstrated to have low resistivity with 1020 ~ 1021 cm−3 of electron concentration. ZnO (AZO) and Ga doped ZnO (GZO) were reported to be ~ 8.5 × 10−5 Ω·cm and ~ 8.1 × 10−5 Ω·cm, respectively, which are comparable with ~ 7.7 × 10−5 Ω·cm of resistivity of In2 O3 (ITO) [10]. ZnO-based TCOs have a relatively large refractive index in the range of
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