Designing band offset of a-SiO:H solar cells for very high open-circuit voltage (1.06 V) by adjusting band gap of p–i–n junction

Abstract

We have matched the world's highest open-circuit voltage (V oc : 1.06 V) achieved to date for a layered structure comprised of a glass/tin oxide (SnO 2 )/hydrogenated amorphous silicon oxide (a-SiO:H) (p-i-n)/back electrode. For the purposes of this study, we adjusted the band gaps of each layer (p-i-n) to improve overall film quality. Fine-tuning of band profiles with reference to activation energy and optical band gap allowed us to offset the conduction band and the valence band of each layer (p-i-n) and thus improve the built-in potential rather than the electron conductivity, Fourier transform infrared spectroscopy, transmittance or reflectance ratio, resulting in a high V oc . To fully exploit the characteristics of wide-bandgap materials and prevent problems with absorbance, we employed commercially available SnO 2 in the front transparent conductive oxide instead of zinc oxide. Using our deposition and evaluation technologies to build a wide-band-gap single solar cell, we succeeded in matching the world's highest V oc of 1.06 V (Eff : 5.38%, J sc : 8.15 mA/cm 2 , FF: 0.624).

Wide bandgap p-type nanocrystalline silicon oxide as window layer for high performance thin-film silicon multi-junction solar cells

“…The V oc improvement with p-SiO x as p-layer can be explained by the increase of the build-in voltage, which is associated with the work function of p-layer and the conduction band offset (CBO) at the p/i interface [15,41]. Since the majority of the p-layer is the p-doped a-SiO x matrix, its work function and CBO with i-layer determine the V bi .…”

High pressure processing of hydrogenated amorphous silicon solar cells: Relation between nanostructure and high open-circuit voltage

“…The same principle may also be applied to engineer the bandgap of hydrogenated amorphous silicon oxide and hydrogenated amorphous silicon carbide alloys which have the potential to achieve higher V oc than a-Si:H in solar cells. [34][35][36][37] FIG. 5.…”

Light management of a-SiOx:H thin film solar cells with hydrogen-reduced p+ buffer at TiO2/p-layer interface

“…On the basis of these light managing techniques, the J sc increased from 9.88 to 11.42 mA/cm 2 . This contributed to the remarkable efficiency of 8.15% by maintaining the absorber thickness of 100 nm that is thinner than that used in any other study (120-350 nm) reported to date [12,14,15,30].…”

“…To further the efficiency, we sought to enhance characteristics of the top cell in terms of open circuit voltage (V oc ) and the response at short-wavelength regions by employing intrinsic amorphous silicon oxide (a-SiO x :H) thin films with wide bandgaps. The a-SiO x :H solar cells delivered better V oc than conventional a-Si:H solar cells [11][12][13][14][15]. However, the efficiency itself was relatively lower than that of a-Si:H cells because of low J sc .…”