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The hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) double p-type window layer has been developed and applied for improving microcrystalline silicon-germanium p-i-n single-junction thin-film solar cells deposited on textured SnO2:F-coated glass substrates. The substrates of SnO2:F, SnO2:F/μc-Si:H(p), and SnO2:F/a-Si:H(p) were exposed to H2plasma to investigate the property change. Our results showed that capping a thin layer of a-Si:H(p) on SnO2:F can minimize the Sn reduction during the deposition process which had H2-containing plasma. Optical measurement has also revealed that a-Si:H(p) capped SnO2:F glass had a higher optical transmittance. When the 20 nmμc-Si:H(p) layer was replaced by a 3 nm a-Si:H(p)/17 nmμc-Si:H(p) double window layer in the cell, the conversion efficiency (η) and the short-circuit current density (JSC) were increased by 16.6% and 16.4%, respectively. Compared to the standard cell with the 20 nmμc-Si:H(p) window layer, an improved conversion efficiency of 6.19% can be obtained for the cell having a-Si:H(p)/μc-Si:H(p) window layer, withVOC = 490 mV,JSC = 19.50 mA/cm2, and FF = 64.83%.

Effects of RF power on optical, electrical, and structural properties ofμc-Si1−xGex:H films was reported. Raman and FTIR spectra fromμc-Si1−xGex:H films reflected the variation in microstructure and bonding configuration. Unlike increasing the germane concentration for Ge incorporation, low RF power enhanced Ge incorporation efficiency inμc-Si1−xGex:H alloy. By decreasing RF power from 100 to 50 W at a fixed reactant gas ratio, the optical bandgap ofμc-Si1−xGex:H was reduced owing to the increase in Ge content from 11.2 to 23.8 at.%, while Ge-related defects and amorphous phase were increased. Consequently, photo conductivity of 1.62 × 10−5 S/cm was obtained for theμc-Si1−xGex:H film deposited at 60 W. By applying 0.9 μm thickμc-Si1−xGex:H absorber withXCof 48% and [Ge] of 16.4 at.% in the single-junction cell, efficiency of 6.18% was obtained. The long-wavelength response ofμc-Si1−xGex:H cell was significantly enhanced compared with theμc-Si:H cell. In the case of tandem cells, 0.24 μm a-Si:H/0.9 μmμc-Si1−xGex:H tandem cell exhibited a comparable spectral response as 0.24 μm a-Si:H/1.4 μmμc-Si:H tandem cell and achieved an efficiency of 9.44%.

This paper presents a feasibility study of a large simulated stadium-scale photovoltaic generation system (PVGS) on a small island. Both the PVGS contribution to the energy demand on the island and its financial analysis were analysed in this study. The maximum allowable PVGS installation capacity is obtained by executing load flow analysis without violating the voltage magnitude and voltage variation ratio limits. However, the estimated power generation of PVGS is applied to know its impact on the power system according to the hourly solar irradiation and temperature. After that, the cost-benefit analysis of payback years (PBY) and net present value (NPV) method is derived considering the cash flow from utilities annual fuel and loss saving, the operation and maintenance (O&M) cost, and the capital investment cost. The power network in Kiribati (PUB DNST) is selected for study in this paper. The simulation results are very valuable and can be applied to the other small islands for reducing the usage of fossil fuel and greenhouse gas emissions.

The enhancement of optical absorption of silicon thin-film solar cells by the p- and n-typeμc-SiOx:H as doped and functional layers was presented. The effects of deposition conditions and oxygen content on optical, electrical, and structural properties ofμc-SiOx:H films were also discussed. Regarding the dopedμc-SiOx:H films, the wide optical band gap (E04) of 2.33 eV while maintaining a high conductivity of 0.2 S/cm could be obtained with oxygen incorporation of 20 at.%. Compared to the conventionalμc-Si:H(p) as window layer inμc-Si:H single-junction solar cells, the application ofμc-SiOx:H(p) increased theVOCand led to a significant enhancement in the short-wavelength spectral response. Meanwhile, the employment ofμc-SiOx:H(n) instead of conventional ITO as back reflecting layer (BRL) enhanced the external quantum efficiency (EQE) ofμc-Si:H single-junction cell in the long-wavelength region, leading to a relative efficiency gain of 10%. Compared to the reference cell, the optimized a-Si:H/μc-Si:H tandem cell by applying p- and n-typeμc-SiOx:H films achieved aVOCof 1.37 V,JSCof 10.55 mA/cm2, FF of 73.67%, and efficiency of 10.51%, which was a relative enhancement of 16%.

Hydrogenated microcrystalline silicon-germanium (μc-Si1-xGex:H) alloys were developed for application in Si-based thin-film solar cells. The effects of thegermane concentration(RGeH4)and thehydrogen ratio(RH2)on theμc-Si1-xGex:H alloys and the corresponding single-junction thin-film solar cells were studied. The behaviors of Ge incorporation in a-Si1-xGex:H andμc-Si1-xGex:H were also compared. Similar to a-Si1-xGex:H, the preferential Ge incorporation was observed inμc-Si1-xGex:H. Moreover, a higherRH2significantly promoted Ge incorporation for a-Si1-xGex:H, while the Ge content was not affected byRH2inμc-Si1-xGex:H growth. Furthermore, to eliminate the crystallization effect, the 0.9 μm thick absorbers with a similar crystalline volume fraction were applied. With the increasingRGeH4, the accompanied increase in Ge content ofμc-Si1-xGex:H narrowed the bandgap and markedly enhanced the long-wavelength absorption. However, the bias-dependent EQE measurement revealed that too much Ge incorporation in absorber deteriorated carrier collection and cell performance. With the optimization ofRH2andRGeH4, the single-junctionμc-Si1-xGex:H cell achieved an efficiency of 5.48%, corresponding to the crystalline volume fraction of 50.5% and Ge content of 13.2 at.%. Compared toμc-Si:H cell, the external quantum efficiency at 800 nm had a relative increase by 33.1%.

We reported the effect of bandgap grading of absorbers on the performance of a-Si1−xGex:H cells employingμc-SiOx:Hn-layer. The influence of bandgap grading widths extended from thep-layer (thep/igrading) and then-layer (thei/ngrading) to the absorber on the cell performance which were systematically studied. Thep/igrading reduced the interface defects and thus improved theVOC. The reducedJSCand FF were presumably due to the degraded hole transport by the potential gradient ofp/igrading. Increasing thei/ngrading width improved the carrier collection significantly. The EQE, theJSC, and the FF were improved substantially. Bias-dependent EQE revealed that the carrier collection is efficient in the cell employing optimali/ngrading. On the other hand, increasing thei/ngrading width was accompanied by the decrease in long-wavelength response which potentially constrained thei/ngrading width. Compared to the cell without grading, the a-Si1−xGex:H cells with optimalp/iandi/ngrading width improved the efficiency from 5.5 to 7.5%.

The effects of H2plasma exposure on optical, electrical, and structural properties of fluorine-doped tin oxide (FTO) and AZO/FTO substrates have been investigated. With increasing the time of H2-plasma exposure, the hydrogen radical and ions penetrated through the FTO surface to form more suboxides such as SnO and metallic Sn, which was confirmed by the XPS analysis. The Sn reduction on the FTO surface can be effectively eliminated by capping the FTO with a very thin layer of sputtered aluminum-doped zinc oxide (AZO), as confirmed by the XPS analysis. By using the AZO/FTO as front TCO with the subsequent annealing, the p-i-nμc-Si:H cell exhibited a significantly enhancedJSCfrom 15.97 to 19.40 mA/cm2and an increased conversion efficiency from 5.69% to 7.09%. This significant enhancement was ascribed to the effective elimination of the Sn reduction on the FTO surface by the thin AZO layer during the Si-based thin-film deposition with hydrogen-rich plasma exposure. Moreover, the subsequent annealing of the sputtered AZO could lead to less defects as well as a better interface of AZO/FTO.