High quality perovskite films with large columnar grains are greatly desired for efficient perovskite solar cells. Here, low volatility N-methyl-2-pyrrolidone(NMP) was added in MAI/IPA solution in a two-step spin-coat...High quality perovskite films with large columnar grains are greatly desired for efficient perovskite solar cells. Here, low volatility N-methyl-2-pyrrolidone(NMP) was added in MAI/IPA solution in a two-step spin-coating method, which promoted the conversion of lead iodide to perovskite. The perovskite films were annealed by a closed-steam annealing method to prolong the recrystallization process of perovskite films assisted by the residual NMP. It leaded to high quality CH_3NH_3PbI_3 perovskite films with large columnar grains due to its enhancement of the Oswald ripening. The large grain perovskite film leaded to efficient carrier transformation and injection, and low recombination. The photovoltaic performance of the perovskite solar cells was improved significantly.展开更多
The AgCuInGa alloy precursors with different Ag concentrations are fabricated by sputtering an Ag target and a CuInGa target.The precursors are selenized in the H_(2)Se-containing atmosphere to prepare(Ag,Cu)(In,Ga)Se...The AgCuInGa alloy precursors with different Ag concentrations are fabricated by sputtering an Ag target and a CuInGa target.The precursors are selenized in the H_(2)Se-containing atmosphere to prepare(Ag,Cu)(In,Ga)Se_(2)(ACIGS)absorbers.The beneficial effects of Ag doping are demonstrated and their mechanism is explained.It is found that Ag doping significantly improves the films crystallinity.This is believed to be due to the lower melting point of chalcopyrite phase obtained by the Ag doping.This leads to a higher migration ability of the atoms that in turn promotes grain boundary migration and improves the film crystallinity.The Ga enrichment at the interface between the absorber and the back electrode is also alleviated during the selenization annealing.It is found that Ag doping within a specific range can passivate the band tail and improve the quality of the films.Therefore,carrier recombination is reduced and carrier transport is improved.The negative effects of excessive Ag are also demonstrated and their origin is revealed.Because the atomic size of Ag is different from that of Cu,for the Ag/(Ag+Cu)ratio(AAC)≥0.030,lattice distortion is aggravated,and significant micro-strain appears.The atomic radius of Ag is close to those of In and Ga,so that the continued increase in AAC will give rise to the Ag;or Ag;defects.Both the structural and compositional defects degrade the quality of the absorbers and the device performance.An excellent absorber can be obtained at AAC of 0.015.展开更多
With the combination of surfactant and freeze-drying, we have developed two kinds of graphene spongy structures. On the one hand, using foams of soap bubbles as templates, three-dimensional porous graphene sponges wit...With the combination of surfactant and freeze-drying, we have developed two kinds of graphene spongy structures. On the one hand, using foams of soap bubbles as templates, three-dimensional porous graphene sponges with rich hierarchical pores have been synthesized. Pores of the material contain three levels of length scales, including millimeter, micrometer and nanometer. The structure can be tuned by changing the freezing media, adjusting the stirring rate or adding functional additives. On the other hand, by direct freeze-drying of a graphene oxide/surfactant suspension, a porous framework with directionally aligned pores is prepared. The surfactant gives a better dispersion of graphene oxide sheets, resulting in a high specific surface area. Both of the obtained materials exhibit excellent absorption capacity and good compression performance, providing a broad range of possible applications, such as absorbents, storage media, and carriers.展开更多
A carbon nanotube (CNT) sponge contains a three-dimensional conductive nano- tube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique ...A carbon nanotube (CNT) sponge contains a three-dimensional conductive nano- tube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole (PPy) core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance (〉 90% of initial value). Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.展开更多
Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride (h-BN) can be used as bendable dielectric due to its wide band gap. He...Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride (h-BN) can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of -9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 F/cm^2, which is one order of magnitude higher than the calculated value.展开更多
Enhancing the mechanical strength of highly conductive pure metals usually causes significant reduction in their electrical conductivity.For example,introducing phase/matrix interfaces or more grain boundaries,are com...Enhancing the mechanical strength of highly conductive pure metals usually causes significant reduction in their electrical conductivity.For example,introducing phase/matrix interfaces or more grain boundaries,are common and effective methods to strengthen metals.But it simultaneously increases the electron scattering at the interface,thus reducing the electrical conductivity.In this study,we demonstrate that pure aluminum(Al)/carbon nanotubes(CNTs)nanocomposites prepared by friction stir processing have successfully broken through these limitations.The yield strength and tensile strength of Al/CNTs nanocomposites have improved by 104.7%and 51.8%compared to pure Al,while the electrical conductivity remained comparable to that of pure Al.To explore the potential mechanisms,the interface between CNTs and Al was examined and characterized by transmission electron microscopy(TEM)and Raman spectroscopy.Little interfacial reaction compounds were present and no visible physical gaps were observed at CNTs and Al interfaces.We defined it as a clean and tightly bonded interface.Although the quantity of phase interface has increased,the electrical conductivity of the nanocomposite remains approximately unchanged.We attribute the preserved electrical conductivity to the clean and tightly bonded CNTs/Al interface in the nanocomposite.展开更多
Detection and analysis of volatile organic compounds (VOCs) as pollutants in the atmosphere and liquids are of great significance because of the detrimental effects of VOCs. A polymer-coated graphene micro-tube pipi...Detection and analysis of volatile organic compounds (VOCs) as pollutants in the atmosphere and liquids are of great significance because of the detrimental effects of VOCs. A polymer-coated graphene micro-tube piping (GMP) structure with a cross-linked and interconnected channel network was synthesized for liquid sensing. By virtue of their unique cross-linked and interconnected channel network configuration, polycrystalline conformation, and the support of a polymer layer, the resistivity of the 3D hollow micro-tubing GMPs was sensitive to strain, ensuring high sensitivity of the liquid sensor (R/Ro of -4 × 10^3% for pure acetone and R/Ro of -105% for 0.01 wt.% acetone solution). Due to the capillary force, the interfaces of the 3D structures can speed up the penetration of solvents into the polymer, thus promote distinct selectivity within seconds and significantly decrease the response time. Owing to their good selectivity, high sensitivity, rapid response and flexibility, and the ease of use of the sensors and the simplicity of the fabrication processes, the GMP/polymer composites should be a good candidate for liquid sensing.展开更多
We have combined two planar nanostructures, graphene and CdSe nanobelts, to construct Schottky junction solar cells with open-circuit voltages of about 0.5 V and cell efficiencies on the order of 0.1%. By covering tra...We have combined two planar nanostructures, graphene and CdSe nanobelts, to construct Schottky junction solar cells with open-circuit voltages of about 0.5 V and cell efficiencies on the order of 0.1%. By covering transparent graphene or carbon nanotube (CNT) films on selected positions along macroscopically long CdSe nanobelts, we have demonstrated the fabrication of active solar cells with many different configurations and parallel connections from individual or multiple assembled nanobelts. The graphene-CdSe nanobelt solar cells reported here show a great flexibility in creating diverse device architectures, and might be scaled up for cell integration based on assembled nanobelt arrays and patterned graphene (or CNT) films.展开更多
The magnetic transitions in graphene oxide (GO) have been investigated experimentally. Micron-sized GO flakes exhibit dominant diamagnetism accompanied by weak ferromagnetism at room temperature. However, when the l...The magnetic transitions in graphene oxide (GO) have been investigated experimentally. Micron-sized GO flakes exhibit dominant diamagnetism accompanied by weak ferromagnetism at room temperature. However, when the lateral dimensions of GO flakes are reduced from micron-size to nano-size, a clear transition from dominant diamagnetism to ferromagnetism is observed. After reducing the GO chemically or thermally, the dominant magnetic properties are not altered markedly except for the gradual enhancement of ferromagnetic components. In contrast, at 2 K, significant paramagnetism is present in both the micron-sized and nano-sized GO sheets. The effects of different functional groups on magnetic transitions in graphene derivatives have been further investigated using on hydroxyl-, carboxyl-, amino- and thiol- functionalized graphene. The results reveal that significant diamagnetism with weak ferromagnetism is present at room temperature in all of these functionalized graphene derivatives and the ability of different functional groups to introduce magnetic moments follows the order -SH 〉 --OH 〉 -COOH, -NH2. Notably, at 5 K, diamagnetism, paramagnetism and ferromagnetism coexist in thiol-, hydroxyl- and carboxyl-functionalized graphene, while amino-graphene exhibits dominant paramagnetism, analogous to the low-temperature magnetism in GO. These results indicate that diamagnetism, paramagnetism and ferromagnetism can coexist in graphene derivatives and magnetic transitions among the three states can be achieved which depend on edge states, vacancies, chemical doping and the attached functional groups. The results obtained may help settle the current controversy about the magnetism of graphene-related materials.展开更多
Carbon nanotube-silicon(CNT-Si)solar cells represent one of the alternative photovoltaic techniques with potential for low cost and high efficiency.Here,we report a method to improve solar cell performance by depositi...Carbon nanotube-silicon(CNT-Si)solar cells represent one of the alternative photovoltaic techniques with potential for low cost and high efficiency.Here,we report a method to improve solar cell performance by depositing conventional transitional metal oxides such as WO_(3)and establishing a collaborative system,in which CNTs are well-embedded within the WO_(3)layer and both of them are in close contact to Si substrate.This unique collaborative system optimizes the overall energy conversion process including the light absorption(antireflection by WO_(3)),carrier separation(forming quasi p-n junction)and charge collection(CNT conductive network throughout the oxide layer).Combining with our previous TiO_(2)-coating and HNO_(3)-doping techniques,a solar cell efficiency of>18%at an active area of 0.09 cm 2(air mass 1.5,100 mW/cm^(2))was achieved.The oxide-enhanced CNT-Si solar cells which integrate the advantages of traditional semiconductors and novel nanostructures represent a promising route toward next-generation high-performance silicon-based photovoltaics.展开更多
We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes (CNTs) as a transparent electrode. A flexible CNT network was transferred onto tile top of a polycrystalline CuI layer, making a c...We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes (CNTs) as a transparent electrode. A flexible CNT network was transferred onto tile top of a polycrystalline CuI layer, making a conformal coating with good contact with the underlying CuI. The solar cells showed power conversion efficiencies in the range of 6% to 10.5%, while the efficiency degradation was less than 10% after the device was stored in air for 8 days. Compared with conventional rigid electrodes such as indium tin oxide (ITO) glass, the flexibility of the CNT films ensures better contact with the active layers and removes the need for press-contact electrodes. Degraded cells can recover their original performance by acid doping of the CNT electrode. Our results suggest that CNT films are suitable electrical contacts for rough materials and structures with an uneven surface.展开更多
基金financially supported by the National Natural Science Foundation of China(Grant No.21463002)Startup Funding of Distinguished Professorship of "1000 Talents Program"(31370086963030)+4 种基金Shenzhen Jiawei Photovoltaic Lighting Co.,Ltd.Tsinghua University Initiative Scientific Research Program(20161080165)Natural Science Foundation of Xinjiang Uygur Autonomous Region(No.2016D01C008)Opening Project of State Key laboratory of Crystal Material(No.KF1610)Scientific Research Program of the Higher Education Institution of Xinjiang(XJEDU2017M038)
文摘High quality perovskite films with large columnar grains are greatly desired for efficient perovskite solar cells. Here, low volatility N-methyl-2-pyrrolidone(NMP) was added in MAI/IPA solution in a two-step spin-coating method, which promoted the conversion of lead iodide to perovskite. The perovskite films were annealed by a closed-steam annealing method to prolong the recrystallization process of perovskite films assisted by the residual NMP. It leaded to high quality CH_3NH_3PbI_3 perovskite films with large columnar grains due to its enhancement of the Oswald ripening. The large grain perovskite film leaded to efficient carrier transformation and injection, and low recombination. The photovoltaic performance of the perovskite solar cells was improved significantly.
基金supported by the analysis support of the State Key Laboratory of New Ceramics and Fine Processing。
文摘The AgCuInGa alloy precursors with different Ag concentrations are fabricated by sputtering an Ag target and a CuInGa target.The precursors are selenized in the H_(2)Se-containing atmosphere to prepare(Ag,Cu)(In,Ga)Se_(2)(ACIGS)absorbers.The beneficial effects of Ag doping are demonstrated and their mechanism is explained.It is found that Ag doping significantly improves the films crystallinity.This is believed to be due to the lower melting point of chalcopyrite phase obtained by the Ag doping.This leads to a higher migration ability of the atoms that in turn promotes grain boundary migration and improves the film crystallinity.The Ga enrichment at the interface between the absorber and the back electrode is also alleviated during the selenization annealing.It is found that Ag doping within a specific range can passivate the band tail and improve the quality of the films.Therefore,carrier recombination is reduced and carrier transport is improved.The negative effects of excessive Ag are also demonstrated and their origin is revealed.Because the atomic size of Ag is different from that of Cu,for the Ag/(Ag+Cu)ratio(AAC)≥0.030,lattice distortion is aggravated,and significant micro-strain appears.The atomic radius of Ag is close to those of In and Ga,so that the continued increase in AAC will give rise to the Ag;or Ag;defects.Both the structural and compositional defects degrade the quality of the absorbers and the device performance.An excellent absorber can be obtained at AAC of 0.015.
基金This work is supported by Beijing Natural Science Foundation (No. 2122027), the National Basic Research Program of China (No. 2011CB013000), the National Natural Science Foundation of China (No. 51372133), and the Tsinghua University Initiative Scientific Research Program (No. 2012Z02102).
文摘With the combination of surfactant and freeze-drying, we have developed two kinds of graphene spongy structures. On the one hand, using foams of soap bubbles as templates, three-dimensional porous graphene sponges with rich hierarchical pores have been synthesized. Pores of the material contain three levels of length scales, including millimeter, micrometer and nanometer. The structure can be tuned by changing the freezing media, adjusting the stirring rate or adding functional additives. On the other hand, by direct freeze-drying of a graphene oxide/surfactant suspension, a porous framework with directionally aligned pores is prepared. The surfactant gives a better dispersion of graphene oxide sheets, resulting in a high specific surface area. Both of the obtained materials exhibit excellent absorption capacity and good compression performance, providing a broad range of possible applications, such as absorbents, storage media, and carriers.
基金This work was supported by the National Natural Science Foundation of China (NSFC, No. 91127004) and the Beijing City Science and Technology Program (No. Z121100001312005).
文摘A carbon nanotube (CNT) sponge contains a three-dimensional conductive nano- tube network, and can be used as a porous electrode for various energy devices. We present here a rational strategy to fabricate a unique CNT@polypyrrole (PPy) core-shell sponge, and demonstrate its application as a highly compressible supercapacitor electrode with high performance. A PPy layer with optimal thickness was coated uniformly on individual CNTs and inter-CNT contact points by electrochemical deposition and crosslinking of pyrrole monomers, resulting in a core-shell configuration. The PPy coating significantly improves specific capacitance of the CNT sponge to above 300 F/g, and simultaneously reinforces the porous structure to achieve better strength and fully elastic structural recovery after compression. The CNT@PPy sponge can sustain 1,000 compression cycles at a strain of 50% while maintaining a stable capacitance (〉 90% of initial value). Our CNT@PPy core-shell sponges with a highly porous network structure may serve as compressible, robust electrodes for supercapacitors and many other energy devices.
基金This work was supported by the National Natural Science Foundation of China (No. 51172122), the Foundation for the Author of National Excellent Doctoral Dissertation (No. 2007B37) and the Program for New Century Excellent Talents in University, the Tsinghua University Initiative Scientific Research Pro-gram (No. 20111080939), and the China Postdoctoral Science Foundation (No. 2011M500310). We thank Prof. Yonggang Zhao and Dr. Xingli Jiang for their help in testing the capacitors.
文摘Highly reliable and bendable dielectrics are desired in flexible or bendable electronic devices for future applications. Hexagonal boron nitride (h-BN) can be used as bendable dielectric due to its wide band gap. Here, we fabricate high quality h-BN films with controllable thickness by a low pressure chemical vapor deposition method. We demonstrate a parallel-plate capacitor using h-BN film as the dielectric. The h-BN capacitors are reliable with a high breakdown field strength of -9.0 MV/cm. Tunneling current across the h-BN film is inversely exponential to the thickness of dielectric, which makes the capacitance drop significantly. The h-BN capacitor shows a best specific capacitance of 6.8 F/cm^2, which is one order of magnitude higher than the calculated value.
文摘Enhancing the mechanical strength of highly conductive pure metals usually causes significant reduction in their electrical conductivity.For example,introducing phase/matrix interfaces or more grain boundaries,are common and effective methods to strengthen metals.But it simultaneously increases the electron scattering at the interface,thus reducing the electrical conductivity.In this study,we demonstrate that pure aluminum(Al)/carbon nanotubes(CNTs)nanocomposites prepared by friction stir processing have successfully broken through these limitations.The yield strength and tensile strength of Al/CNTs nanocomposites have improved by 104.7%and 51.8%compared to pure Al,while the electrical conductivity remained comparable to that of pure Al.To explore the potential mechanisms,the interface between CNTs and Al was examined and characterized by transmission electron microscopy(TEM)and Raman spectroscopy.Little interfacial reaction compounds were present and no visible physical gaps were observed at CNTs and Al interfaces.We defined it as a clean and tightly bonded interface.Although the quantity of phase interface has increased,the electrical conductivity of the nanocomposite remains approximately unchanged.We attribute the preserved electrical conductivity to the clean and tightly bonded CNTs/Al interface in the nanocomposite.
基金Acknowledgements This work was supported by National Science Foundation of China (Nos. 51372133 and 91323304), Beijing Science and Technology Program (No. D141100000514001), and Beijing Natural Science Foundation (No. 2122027).
文摘Detection and analysis of volatile organic compounds (VOCs) as pollutants in the atmosphere and liquids are of great significance because of the detrimental effects of VOCs. A polymer-coated graphene micro-tube piping (GMP) structure with a cross-linked and interconnected channel network was synthesized for liquid sensing. By virtue of their unique cross-linked and interconnected channel network configuration, polycrystalline conformation, and the support of a polymer layer, the resistivity of the 3D hollow micro-tubing GMPs was sensitive to strain, ensuring high sensitivity of the liquid sensor (R/Ro of -4 × 10^3% for pure acetone and R/Ro of -105% for 0.01 wt.% acetone solution). Due to the capillary force, the interfaces of the 3D structures can speed up the penetration of solvents into the polymer, thus promote distinct selectivity within seconds and significantly decrease the response time. Owing to their good selectivity, high sensitivity, rapid response and flexibility, and the ease of use of the sensors and the simplicity of the fabrication processes, the GMP/polymer composites should be a good candidate for liquid sensing.
基金This work was supported by the National Science Foundation of China (NSFC) under grant number 51072005. H. W. Zhu acknowledges the support by theNational Science Foundation of China (No. 50972067), Tsinghua National Laboratory for Information Science and Technology (TNList) Cross-discipline Foundation and Foundation for the Authors of National Excellent Doctoral Dissertations (No. 201038). We acknowledge Yan Li from College of Chemistry in Peking University for help in Raman measurement.
文摘We have combined two planar nanostructures, graphene and CdSe nanobelts, to construct Schottky junction solar cells with open-circuit voltages of about 0.5 V and cell efficiencies on the order of 0.1%. By covering transparent graphene or carbon nanotube (CNT) films on selected positions along macroscopically long CdSe nanobelts, we have demonstrated the fabrication of active solar cells with many different configurations and parallel connections from individual or multiple assembled nanobelts. The graphene-CdSe nanobelt solar cells reported here show a great flexibility in creating diverse device architectures, and might be scaled up for cell integration based on assembled nanobelt arrays and patterned graphene (or CNT) films.
基金This work is supported by the National Natural Science Foundation of China (No. 51372133), the Beijing Science and Technology Program (No. D141100000514001), the National Program on Key Basic Research Projects (Nos. 2013CB934201, 2011CB013000), and the Tsinghua University Initiative Scientific Research Program (No. 2012Z02102).
文摘The magnetic transitions in graphene oxide (GO) have been investigated experimentally. Micron-sized GO flakes exhibit dominant diamagnetism accompanied by weak ferromagnetism at room temperature. However, when the lateral dimensions of GO flakes are reduced from micron-size to nano-size, a clear transition from dominant diamagnetism to ferromagnetism is observed. After reducing the GO chemically or thermally, the dominant magnetic properties are not altered markedly except for the gradual enhancement of ferromagnetic components. In contrast, at 2 K, significant paramagnetism is present in both the micron-sized and nano-sized GO sheets. The effects of different functional groups on magnetic transitions in graphene derivatives have been further investigated using on hydroxyl-, carboxyl-, amino- and thiol- functionalized graphene. The results reveal that significant diamagnetism with weak ferromagnetism is present at room temperature in all of these functionalized graphene derivatives and the ability of different functional groups to introduce magnetic moments follows the order -SH 〉 --OH 〉 -COOH, -NH2. Notably, at 5 K, diamagnetism, paramagnetism and ferromagnetism coexist in thiol-, hydroxyl- and carboxyl-functionalized graphene, while amino-graphene exhibits dominant paramagnetism, analogous to the low-temperature magnetism in GO. These results indicate that diamagnetism, paramagnetism and ferromagnetism can coexist in graphene derivatives and magnetic transitions among the three states can be achieved which depend on edge states, vacancies, chemical doping and the attached functional groups. The results obtained may help settle the current controversy about the magnetism of graphene-related materials.
基金the Natural Science Foundation of Beijing(No.2212028)the Natural Science Foundation of Henan province(No.202300410371)+1 种基金the National Natural Science Foundation of China(Nos.51325202 and 51872267)the National Key Research and Development Program(No.2020YFA0210702).
文摘Carbon nanotube-silicon(CNT-Si)solar cells represent one of the alternative photovoltaic techniques with potential for low cost and high efficiency.Here,we report a method to improve solar cell performance by depositing conventional transitional metal oxides such as WO_(3)and establishing a collaborative system,in which CNTs are well-embedded within the WO_(3)layer and both of them are in close contact to Si substrate.This unique collaborative system optimizes the overall energy conversion process including the light absorption(antireflection by WO_(3)),carrier separation(forming quasi p-n junction)and charge collection(CNT conductive network throughout the oxide layer).Combining with our previous TiO_(2)-coating and HNO_(3)-doping techniques,a solar cell efficiency of>18%at an active area of 0.09 cm 2(air mass 1.5,100 mW/cm^(2))was achieved.The oxide-enhanced CNT-Si solar cells which integrate the advantages of traditional semiconductors and novel nanostructures represent a promising route toward next-generation high-performance silicon-based photovoltaics.
基金This work is supported by the National Natural Science Foundation of China (NSFC, Grant No.50972067) and the 863 Program (No. 2009AA05Z423). A. Cao acknowledges the support by the National Science Foundation of China (NSFC, No. 51072005) and C. Huang acknowledges NSFC No. 90922004 for financial support.
文摘We report the fabrication of CuI-Si heterojunction solar cells with carbon nanotubes (CNTs) as a transparent electrode. A flexible CNT network was transferred onto tile top of a polycrystalline CuI layer, making a conformal coating with good contact with the underlying CuI. The solar cells showed power conversion efficiencies in the range of 6% to 10.5%, while the efficiency degradation was less than 10% after the device was stored in air for 8 days. Compared with conventional rigid electrodes such as indium tin oxide (ITO) glass, the flexibility of the CNT films ensures better contact with the active layers and removes the need for press-contact electrodes. Degraded cells can recover their original performance by acid doping of the CNT electrode. Our results suggest that CNT films are suitable electrical contacts for rough materials and structures with an uneven surface.