Passivation ability of graphene oxide demonstrated by two-different-metal solar cells
© Hsu et al.; licensee Springer. 2014
Received: 27 June 2014
Accepted: 10 December 2014
Published: 23 December 2014
The study on graphene oxide (GO) grows rapidly in recent years. We find that graphene oxide could act as the passivation material in photovoltaic applications. Graphene oxide has been applied on Si two-different-metal solar cells. The suitable introduction of graphene oxide could result in obvious enhancement on the efficiency. The simple chemical process to deposit graphene oxide makes low thermal budget, large-area deposition, and fast production of surface passivation possible. The different procedures to incorporate graphene oxide in Si two-different-metal solar cells are compared, and 21% enhancement on the efficiency is possible with a suitable deposition method.
KeywordsPassivation Solar cell Graphene oxide Two-different-metal Hummers method
Energy from solar cells has been thought as the possible alternative to the traditional fuel energy. In order to compete with the traditional energy, increase on the efficiency of solar cells in a cost-effective way is important. For a solar module with an efficiency of 20%, 1% improvement on efficiency can correspond to 5% reduction in cost. Surface structures[1–3] and passivation[4–7] can be utilized to improve the efficiency. Passivation of bare Si surfaces can be easily achieved with hydrogen termination, alkylation, and so on, but the effect may deteriorate in a certain time. Passivation by dielectric films, such as SiO2, SiNx, and Al2O3 could overcome the stability issue. The high-quality SiO2 is common oxide for surface passivation of Si solar cells. Al2O3 prepared by atomic layer deposition is also used due to its promising ability of passivation for Si, especially for the p-type Si. Since various oxide materials have been used for passivation of solar cells, we would like to investigate the effect of graphene oxide (GO) as the passivation layer. GO is broadly studied after the developing of graphene in recent years[9–11]. The above mentioned oxide passivation films are almost demonstrated in chambers, and GO deposited in chemical solution may be a much simpler method. For the photovoltaic applications, GO has been adopted in organic solar cells as the hole transport layer. We will apply GO to Si solar cells with the purpose of surface passivation. The different procedures to incorporate GO in Si two-different-metal solar cells are compared. To the best of our knowledge, GO has not been utilized on the applications of solar cell passivation. The chemical solution method makes the low thermal budget, large-area deposition, and fast production possible.
Results and discussion
The passivation effect of GO is supposed due to the field effect passivation contributed by the negative fixed charge in GO as verified in ref.. In ref., the capacitance verse voltage relation of GO and control metal-insulator-semiconductor (MIS) capacitors were compared. The curves of MIS capacitors with GO coated shifted to the positive-bias direction, and it meant that extra negative charge existed in GO. Such a dielectric GO film with negative fixed charge could be used to passivate solar cells, especially for the p-side. For our two-different-metal solar cells, GO can be coated on the rear side of the p-type Si substrate. Without GO being coated, many of the photo-generated electron-hole pairs may easily recombine at the rear surface due to the termination of the periodic Si structure. With GO coated, minority carriers (electrons) can be repelled from the surface. Since recombination should only occur between an electron and a hole, the repulsion of electron from the surface could contribute to the decrease of recombination. More electrons can be collected by the Al electrode successfully, and hence, more holes can be collected by the Au electrode. That is why SiGb1 and SiGb2 show the better performance as compared with the ConSi.
Silicon nitride (SiNx) is a common passivation film for solar cells. We have also prepared a two-different-metal solar cell with SiNx on the rear side for comparison. First, we demonstrated another control two-different-metal solar cell, ConSi2, and its IV characteristic under AM 1.5 G illumination was obtained as shown in the inset of Figure 2. Then, the native oxide on the rear side of ConSi2 was removed by buffered oxide etch (BOE). SiNx was subsequently deposited on the rear side by the sputter. Its IV characteristic is also shown in the inset of Figure 2 as the curve of ‘ConSi2 with SiNx’. It can be found that the performance of ‘ConSi2 with SiNx’ is even worse than ConSi2. One reason for the degradation may be due to the un-optimized facility for passivation. The sputter SiNx might have poor quality as compared with the commercial PECVD SiNx. The other reason is that SiNx with positive fixed charge is more suitable for passivation of n-Si substrates instead of p-Si substrates in our case.
Because the best GO cell, SiGb1, has been immersed in the GO suspension for 40 min, it may be suspected that the performance enhancement is due to the more oxidation in water (in GO suspension) but not GO deposition. We prepared two extra control samples. One was immersed in DI water, and the other was rear-side down floating on the water surface of GO suspension to have the similar immersion condition but avoid GO deposition. These two control samples after immersion did not show better cell performance than the results before immersion (not shown here), indicating that the improvement was indeed only due to the GO passivation on the surface.
GO is first-time proven to have the ability to enhance the performance of a solar cell by surface passivation due to its negative fixed charge. GO provides the potential on low-cost and large-area passivation. In the current stage, the simple two-different-metal structure is adopted as the beginning. Further optimization on deposition conditions and light transmission is deserved. More efforts should be made to incorporate the benefit of GO in commercial Si pn solar cells.
This work is supported by National Science Council of R.O.C. under contract no. NSC 101-2221-E-259-023-MY3.
- Cacciato A, Duerinckx F, Baert K, Moors M, Caremans T, Leys G, Keersmaecker K, De Szlufcik J: Investigating manufacturing options for industrial PERL-type Si solar cells. Sol Energy Mater Sol Cells 2013, 113: 153–159.View ArticleGoogle Scholar
- Chen TG, Huang BY, Chen EC, Yu P, Meng HF: Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency. Appl Phys Lett 2012, 101: 033301. 10.1063/1.4734240View ArticleGoogle Scholar
- Ha JM, Yoo SH, Cho JH, Cho YH, Cho SO: Enhancement of antireflection property of silicon using nanostructured surface combined with a polymer deposition. Nanoscale Res Lett 2014, 9: 9. 10.1186/1556-276X-9-9View ArticleGoogle Scholar
- Sameshima T, Kogure K, Hasumi M: High-quality surface passivation of silicon using native oxide and silicon nitride layers. Appl Phys Lett 2012, 101: 021601. 10.1063/1.4733336View ArticleGoogle Scholar
- Chen J, Cornagliotti E, Loozen X, Simoen E, Vanhellemont J, Lauwaert J, Vrielinck H, Poortmans J: Impact of firing on surface passivation of p-Si by SiO2/Al and SiO2/SiNx/Al stacks. J Appl Phys 2011, 110: 126101. 10.1063/1.3669405View ArticleGoogle Scholar
- Schmidt J, Merkle A, Brendel R, Hoex B, van de Sanden MCM, Kessels WMM: Surface passivation of high-efficiency silicon solar cells by atomic-layer-deposited Al2O3. Prog Photovolt 2008, 16: 461–466. 10.1002/pip.823View ArticleGoogle Scholar
- Zhao Y, Zhou C, Zhang X, Zhang P, Dou Y, Wang W, Cao X, Wang B, Tang Y, Zhou S: Passivation mechanism of thermal atomic layer-deposited Al2O3 films on silicon at different annealing temperatures. Nanoscale Res Lett 2013, 8: 114. 10.1186/1556-276X-8-114View ArticleGoogle Scholar
- Royea WJ, Juang A, Lewis NS: Preparation of air-stable, low recombination velocity Si(111) surfaces through alkyl termination. Appl Phys Lett 2000, 77: 1988–1990. 10.1063/1.1312203View ArticleGoogle Scholar
- Joshi RK, Carbone P, Wang FC, Kravets VG, Su Y, Grigorieva IV, Wu HA: Precise and ultrafast molecular sieving through graphene oxide membranes. Science 2014, 343: 752–754. 10.1126/science.1245711View ArticleGoogle Scholar
- Wang W, Li Z, Duan J, Wang C, Fang Y, Yang XD: In vitro enhancement of dendritic cell-mediated anti-glioma immune response by graphene oxide. Nanoscale Res Lett 2014, 9: 311. 10.1186/1556-276X-9-311View ArticleGoogle Scholar
- Liu J, Kim GH, Xue Y, Kim JY, Baek JB, Durstock M: Graphene oxide nanoribbon as hole extraction layer to enhance efficiency and stability of polymer solar cells. Adv Mater 2014, 26: 786–790. 10.1002/adma.201302987View ArticleGoogle Scholar
- Li SS, Tu KH, Lin CC, Chen CW, Chhowalla M: Solution-processable graphene oxide as an efficient hole transport layer in polymer solar cells. ACS Nano 2010, 4: 3169–3174. 10.1021/nn100551jView ArticleGoogle Scholar
- Sameshima T, Kogure K, Hasumi M: Crystalline silicon solar cells with two different metals. Jpn J Appl Phys 2010, 49: 110205. 10.1143/JJAP.49.110205View ArticleGoogle Scholar
- Lin CH, Yeh WT, Chan CH, Lin CC: Influence of graphene oxide on metal-insulator-semiconductor tunneling diodes. Nanoscale Res Lett 2012, 7: 343. 10.1186/1556-276X-7-343View ArticleGoogle Scholar
- Lin CH, Yeh WT, Chen MH: Metal-insulator-semiconductor photodetectors with different coverage ratios of graphene oxide. IEEE J Sel Top Quantum Electron 2014, 20: 3800105.Google Scholar
- Wang X, Zhi L, Müllen K: Transparent, conductive graphene electrodes for dye-sensitized solar cells. Nano Lett 2008, 8: 323–327. 10.1021/nl072838rView ArticleGoogle Scholar
- Singh P, Ravindra NM: Temperature dependence of solar cell performance-an analysis. Sol Energy Mater Sol Cells 2012, 101: 36–45.View ArticleGoogle Scholar
- Hoex B, Schmidt J, Pohl P, van de Sanden MCM, Kessels WMM: Silicon surface passivation by atomic layer deposited Al2O3. J Appl Phys 2008, 104: 044903. 10.1063/1.2963707View ArticleGoogle Scholar
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited.