Performance Enhancement of a Graphene-Zinc Phosphide Solar Cell Using the Electric Field-Effect

Abstract

ABSTRACT:The optical transparency and high electron mobility of graphene make it an attractive material for photovoltaics. We present a field-effect solar cell using graphene to form a tunable junction barrier with an Earth-abundant and low cost zinc phosphide (Zn 3 P 2 ) thin-film light absorber. Adding a semitransparent top electrostatic gate allows for tuning of the graphene Fermi level and hence the energy barrier at the graphene-Zn 3 P 2 junction, going from an ohmic contact at negative gate voltages to a rectifying barrier at positive gate voltages. We perform current and capacitance measurements at different gate voltages in order to demonstrate the control of the energy barrier and depletion width in the zinc phosphide. Our photovoltaic measurements show that the efficiency conversion is increased 2-fold when we increase the gate voltage and the junction barrier to maximize the photovoltaic response. At an optimal gate voltage of +2 V, we obtain an open-circuit voltage of V oc = 0.53 V and an efficiency of 1.9% under AM 1.5 1-sun solar illumination. This work demonstrates that the field effect can be used to modulate and optimize the response of photovoltaic devices incorporating graphene. KEYWORDS: Graphene, zinc phosphide, field effect solar cell, Schottky barrier, earth-abundant materials, photovoltaics T he extraordinary properties of graphene, such as its high carrier mobility, Fermi-level tuning and its high optical transparency, make it an attractive candidate to improve the performance of optoelectronic and photovoltaic devices. 1−3 These properties can be exploited for tackling some of the major challenges in solar energy. One challenge is to exploit Earth-abundant and low-cost synthesis materials with band gaps suitable for solar energy conversion. Besides common PV absorbers like Si, CdTe, and CIGS, there are other materials that have the potential for large scale solar implementation at lower costs, such as zinc phosphide (Zn 3 P 2 ), copper zinc tin sulfide (CZTS), cuprous oxide (Cu 2 O), and iron sulfide (FeS 2 ). 4 However, the lack of doping processes necessary to form homojuntions and the absence of complementary emitter materials to form high quality p−n heterojunction have limited the conversion efficiency of devices incorporating these materials. These limitations can be addressed using graphene, which has previously been used to form graphene−semiconductor junctions 5 and solar cells with CdS and CdSe 6,7 semiconductors as well as with Si,5,[8][9][10][11] demonstrating Schottky barrier behavior. 5 Further advances on graphene−semiconductor junctions were demonstrated by building gate-controlled devices in order to modify the Schottky barrier height and the electrical transport across the junction. This design has been used to build a graphene−Si transistor (barristor) 12 and a graphene−organic thin film junction transistors. 9,13 Herein, we study the barrier tuning of a graphene−Zn 3 P 2 field-effect solar cell with a semitransparent top-gate electrode and demonstrate that this tunin...

18.5% efficient graphene/GaAs van der Waals heterostructure solar cell

“…[25][26][27][28][29] Distinct from traditional Schottky diode, the barrier height of graphene/semiconductor Schottky diode is tunable as the Fermi level of graphene and semiconductor can be adjusted independently benefiting from the nature of van der Waals contact, the low density of energy states near Dirac point and small screening length of graphene. [30,31] Although the tunable barrier height is the key to the physical picture of graphene/semiconductor Schottky diode, and structures with thin metal, ferroelectric polymer and ionic liquid as gating layer have been employed in graphene based electronic and optoelectronic devices [32][33][34][35][36][37][38][39][40], its applications in solar cell has not been explored systemically and the performance needs to further improved. Recently, Vazquez-Mena et al reported thin Au layer gated graphene/zinc phosphide solar cell with power conversion efficiency (PCE) of 1.9%, which is still low considering the relatively large band gap of zinc phosphide of 1.5 eV.…”

“…Recently, Vazquez-Mena et al reported thin Au layer gated graphene/zinc phosphide solar cell with power conversion efficiency (PCE) of 1.9%, which is still low considering the relatively large band gap of zinc phosphide of 1.5 eV. [32] We have achieved PCE of 5.6% in graphene/InP heterostructure solar cell through tuning the Fermi level of graphene by gating effect [41]. The state of art PCE of graphene/semiconductor Schottky diode is 15.6% as achieved in graphene/Si system.…”

Human‐Like Sensing and Reflexes of Graphene‐Based Films

“…Copyright 2015, Royal Society of Chemistry. d) Reproduced with permission 81. Copyright 2014, American Chemical Society.…”

“…Zettl et al presented a new type of field‐effect SC utilizing graphene and zinc phosphide (Zn 3 P 2 ) to form a tunable junction barrier thin‐film light absorber 81. To control the junction barrier between the graphene and a semiconductor, the Fermi level tuning of graphene is the key point.…”

Effects of Sulfurization Pressure on the Conversion Efficiency of Cosputtered Cu2ZnSnS4Thin Film Solar Cells

“…Meanwhile, several fabrication techniques have been adopted to prepare high performance thin film solar cells by using abundant materials. The absorber layer for the thin film solar cells can be prepared by various methods like sputtering, evaporation, electrodeposition, sol gel techniques, and spray pyrolysis [1][2][3][4][5][6][7][8][9][10][11], using abundant materials such as kesterite Cu 2 ZnSnS 4 (CZTS) [2], Cu 2 SnS 3 [12], Cu 2 S [13], SnS [14], Zn 3 P 2 [15], and hybrid perovskite CH 3 NH 3 PbI 3 [16][17][18]. In particular, the sputtering deposition technique has the advantages of easy control and tuning of the material composition of the film.…”