共查询到20条相似文献,搜索用时 31 毫秒
1.
The effect of injection and extraction barriers on flat heterojunction (FHJ) and bulk heterojunction (BHJ) organic solar cells is analyzed. The barriers are realized by a combination of p‐type materials with HOMOs varying between –5.0 and –5.6 eV as hole‐transport layer (HTL) and as donor in vacuum‐evaporated multilayer p‐i‐metal small‐molecule solar cells. The HTL/donor interface can be seen as a model for the influence of contacts in organic solar cells in general. Using drift‐diffusion simulations we are well able to reproduce and explain the experimental I–V curves qualitatively. In FHJ solar cells the open‐circuit voltage (Voc) is determined by the donor and is independent of the HTL. In BHJ solar cells, however, Voc decreases if injection barriers are present. This different behavior is caused by a blocking of the charge carriers at a spatially localized donor/acceptor heterojunction, which is only present in the FHJ solar cells. The forward current is dominated by the choice of HTL. An energy mismatch in the HOMOs leads to kinks in the I–V curves in the cases for which Voc is independent of the HTL. 相似文献
2.
Mikio Taguchi Akira Terakawa Eiji Maruyama Makoto Tanaka 《Progress in Photovoltaics: Research and Applications》2005,13(6):481-488
We have achieved a very high conversion efficiency of 21·5% in HIT cells with a size of 100·3 cm2. One of the most striking features of the HIT cell is its high open‐circuit voltage Voc, in excess of 710 mV. This is due to the excellent surface passivation at the a‐Si/c‐Si heterointerface realized by Sanyo's successful technologies for fabricating high‐quality a‐Si films and solar cells with low plasma damage processes. We have studied ways to treat the surface to produce a good interface throughout our fabrication processes. We have also investigated the deposition conditions of a‐Si layers for optimizing the barrier height for the minority carriers in the heterojunction. Our approach for obtaining HIT cells with a high Voc is reviewed here. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
3.
Bernhard Michl Davide Impera Martin Bivour Wilhelm Warta Martin C. Schubert 《Progress in Photovoltaics: Research and Applications》2014,22(5):581-586
We show the benefits of spatially resolved pseudo fill factor analysis on multicrystalline silicon solar cells. Hereby, we present a method based on quasi‐steady‐state photoluminescence‐calibrated photoluminescence images at varying generation rate. We verify the method by a comparison with global and local Suns‐Voc measurements and apply Suns‐PLI to multicrystalline heterojunction samples with and without conductive top layer, the latter being not accessible by Suns‐Voc. Thereby, we obtain detailed insight into the influence of injection‐dependent local recombination on fill factor and of losses only due to recombination‐driven lateral balancing currents. The conclusions are supported by Spice network simulations. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
4.
Shui‐Yang Lien Dong‐Sing Wuu 《Progress in Photovoltaics: Research and Applications》2009,17(7):489-501
In this paper, we will present a Pc1D numerical simulation for heterojunction (HJ) silicon solar cells, and discuss their possibilities and limitations. By means of modeling and numerical computer simulation, the influence of emitter‐layer/intrinsic‐layer/crystalline‐Si heterostructures with different thickness and crystallinity on the solar cell performance is investigated and compared with hot wire chemical vapor deposition (HWCVD) experimental results. A new technique for characterization of n‐type microcrystalline silicon (n‐µc‐Si)/intrinsic amorphous silicon (i‐a‐Si)/crystalline silicon (c‐Si) heterojunction solar cells from Pc1D is developed. Results of numerical modeling as well as experimental data obtained using HWCVD on µc‐Si (n)/a‐Si (i)/c‐Si (p) heterojunction are presented. This work improves the understanding of HJ solar cells to derive arguments for design optimization. Some simulated parameters of solar cells were obtained: the best results for Jsc = 39·4 mA/cm2, Voc = 0·64 V, FF = 83%, and η = 21% have been achieved. After optimizing the deposition parameters of the n‐layer and the H2 pretreatment of solar cell, the single‐side HJ solar cells with Jsc = 34·6 mA/cm2, Voc = 0·615 V, FF = 71%, and an efficiency of 15·2% have been achieved. The double‐side HJ solar cell with Jsc = 34·8 mA/cm2, Voc = 0·645 V, FF = 73%, and an efficiency of 16·4% has been fabricated. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
5.
Youngseok Lee Vinh Ai Dao S. M. Iftiquar Sangho Kim Junsin Yi 《Progress in Photovoltaics: Research and Applications》2016,24(1):52-58
This paper presents an understanding of the fundamental carrier transport mechanism in hydrogenated amorphous silicon (a‐Si:H)‐based n/p junctions. These n/p junctions are, then, used as tunneling and recombination junctions (TRJ) in tandem solar cells, which were constructed by stacking the a‐Si:H‐based solar cell on the heterojunction with intrinsic thin layer (HIT) cell. First, the effect of activation energy (Ea) and Urbach parameter (Eu) of n‐type hydrogenated amorphous silicon (a‐Si:H(n)) on current transport in an a‐Si:H‐based n/p TRJ has been investigated. The photoluminescence spectra and temperature‐dependent current–voltage characteristics in dark condition indicates that the tunneling is the dominant carrier transport mechanism in our a‐Si:H‐based n/p‐type TRJ. The fabrication of a tandem cell structure consists of an a‐Si:H‐based top cell and an HIT‐type bottom cell with the a‐Si:H‐based n/p junction developed as a TRJ in between. The development of a‐Si:H‐based n/p junction as a TRJ leads to an improved a‐Si:H/HIT‐type tandem cell with a better open circuit voltage (Voc), fill factor (FF), and efficiency. The improvements in the cell performance was attributed to the wider band‐tail states in the a‐Si:H(n) layer that helps to an enhanced tunneling and recombination process in the TRJ. The best photovoltage parameters of the tandem cell were found to be Voc = 1430 mV, short circuit current density = 10.51 mA/cm2, FF = 0.65, and efficiency = 9.75%. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
6.
Elucidating the Origins of Subgap Tail States and Open‐Circuit Voltage in Methylammonium Lead Triiodide Perovskite Solar Cells
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tian Du Jinhyun Kim Jonathan Ngiam Shengda Xu Piers R. F. Barnes James R. Durrant Martyn A. McLachlan 《Advanced functional materials》2018,28(32)
Recombination via subgap trap states is considered a limiting factor in the development of organometal halide perovskite solar cells. Here, the impact of active layer crystallinity on the accumulated charge and open‐circuit voltage (Voc) in solar cells based on methylammonium lead triiodide (CH3NH3PbI3, MAPI) is demonstrated. It is shown that MAPI crystallinity can be systematically tailored by modulating the stoichiometry of the precursor mix, where small quantities of excess methylammonium iodide (MAI) improve crystallinity, increasing device Voc by ≈200 mV. Using in situ differential charging and transient photovoltage measurements, charge density and charge carrier recombination lifetime are determined under operational conditions. Increased Voc is correlated to improved active layer crystallinity and a reduction in the density of trap states in MAPI. Photoluminescence spectroscopy shows that an increase in trap state density correlates with faster carrier trapping and more nonradiative recombination pathways. Fundamental insights into the origin of Voc in perovskite photovoltaics are provided and it is demonstrated why highly crystalline perovskite films are paramount for high‐performance devices. 相似文献
7.
Petr P. Khlyabich Andrey E. Rudenko Barry C. Thompson Yueh‐Lin Loo 《Advanced functional materials》2015,25(34):5557-5563
Ternary‐blend bulk‐heterojunction solar cells have provided a unique opportunity for tuning the open‐circuit voltage (Voc) as the “effective” highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) energy levels shift with active‐layer composition. Grazing‐incidence X‐ray diffraction (GIXD) measurements performed on such ternary‐blend thin films reveal evidence that the two polymer donors interact intimately; their ionization potentials are thus reflections of the blend compositions. In ternary‐blend thin films in which the two polymer donors do not interact physically, the polymer donors each retain their molecular electronic character; solar cells constructed with these ternary blends thus exhibit Vocs that are pinned to the energy level difference between the highest of the two lying HOMO and the LUMO of the electron acceptor. These observations are consistent with the organic alloy model proposed earlier. Quantification of the square of the square‐root differences of the surface energies of the components provides a proxy for the Flory–Huggins interaction parameter for polymer donor pairs in these ternary‐blend systems. Of the three ternary‐blend systems examined herein, this quantity has to be below 0.094 in order for ternary‐blend solar cells to exhibit tunable Voc. 相似文献
8.
Functionalization of Graphene Oxide Films with Au and MoOx Nanoparticles as Efficient p‐Contact Electrodes for Inverted Planar Perovskite Solar Cells
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Sumit S. Bhosale Efat Jokar Amir Fathi Cheng‐Min Tsai Chi‐Yung Wang Eric Wei‐Guang Diau 《Advanced functional materials》2018,28(37)
A graphene oxide (GO) film is functionalized with metal (Au) and metal‐oxide (MoOx) nanoparticles (NPs) as a hole‐extraction layer for high‐performance inverted planar‐heterojunction perovskite solar cells (PSCs). These NPs can increase the work function of GO, which is confirmed with X‐ray photoelectron spectra, Kelvin probe force microscopy, and ultraviolet photoelectron spectra measurements. The down‐shifts of work functions lead to a decreased level of potential energy and hence increased Voc of the PSC devices. Although the GO‐AuNP film shows rapid hole extraction and increased Voc, a Jsc improvement is not observed because of localization of the extracted holes inside the AuNP that leads to rapid charge recombination, which is confirmed with transient photoelectric measurements. The power conversion efficiency (PCE) of the GO‐AuNP device attains 14.6%, which is comparable with that of the GO‐based device (14.4%). In contrast, the rapid hole extraction from perovskite to the GO‐MoOx layer does not cause trapping of holes and delocalization of holes in the GO film accelerates rapid charge transfer to the indium tin oxide substrate; charge recombination in the perovskite/GO‐MoOx interface is hence significantly retarded. The GO‐MoOx device consequently shows significantly enhanced Voc and Jsc, for which its device performance attains PCE of 16.7% with great reproducibility and enduring stability. 相似文献
9.
Surface modification of indium tin oxide (ITO)‐coated substrates through the use of self‐assembled monolayers (SAMs) of molecules with permanent dipole moments has been used to control the anode work function and device performance in molecular solar cells based on a CuPc:C60 (CuPc: copper phthalocyanine) heterojunction. Use of SAMs increases both the short‐circuit current density (Jsc) and fill factor, increasing the power‐conversion efficiency by up to an order of magnitude. This improvement is attributed primarily to an enhanced interfacial charge transfer rate at the anode, due to both a decrease in the interfacial energy step between the anode work function and the highest occupied molecular orbital (HOMO) level of the organic layer, and a better compatibility of the SAM‐modified electrodes with the initial CuPc layers, which leads to a higher density of active sites for charge transfer. An additional factor may be the influence of increasing electric field at the heterojunction on the exciton‐dissociation efficiency. This is supported by calculations of the electric potential distribution for the structures. Work‐function modification has virtually no effect on the open‐circuit voltage (Voc), in accordance with the idea that Voc is controlled primarily by the energy levels of the donor and acceptor materials. 相似文献
10.
Ji Wan Lifu Zhang Qiannan He Siqi Liu Bin Huang Lei Hu Weihua Zhou Yiwang Chen 《Advanced functional materials》2020,30(14)
The vast majority of ternary organic solar cells are obtained by simply fabricating bulk heterojunction (BHJ) active layers. Due to the inappropriate distribution of donors and acceptors in the vertical direction, a new method by fabricating pseudoplanar heterojunction (PPHJ) ternary organic solar cells is proposed to better modulate the morphology of active layer. The pseudoplanar heterojunction ternary organic solar cells (P‐ternary) are fabricated by a sequential solution treatment technique, in which the donor and acceptor mixture blends are sequentially spin‐coated. As a consequence, a higher power conversion efficiency (PCE) of 14.2% is achieved with a Voc of 0.79 V, Jsc of 25.6 mA cm?2, and fill factor (FF) of 69.8% compared with the ternary BHJ system of 13.8%. At the same time, the alloyed acceptor is likely formed between two the acceptors through a series of in‐depth explorations. This work suggests that nonfullerene alloyed acceptor may have great potential to realize effective P‐ternary organic solar cells. 相似文献
11.
Effects of Nonradiative Losses at Charge Transfer States and Energetic Disorder on the Open‐Circuit Voltage in Nonfullerene Organic Solar Cells
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Shenkun Xie Yuxin Xia Zhong Zheng Xuning Zhang Jianyu Yuan Huiqiong Zhou Yuan Zhang 《Advanced functional materials》2018,28(5)
The considerable improvement on the power conversion efficiency (PCE) for emerging nonfullerene polymer solar cells is still limited by considerable voltage losses that have become one of the most significant obstacles in further boosting desired photovoltaic performance. Here, a comprehensive study is reported to understand the impacts of charge transport, energetic disorder, and charge transfer states (CTS) on the losses in open‐circuit voltage (Voc) based on three high performing bulk heterojunction solar cells with the best PCE exceeding 11%. It is found that the champion poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo[1,2‐b:4,5‐b′]dithiophene)‐co‐(1,3‐di(5‐thiophene‐2‐yl)‐5,7‐bis(2‐ethylhexyl)‐benzo[1,2‐c:4,5‐c′]dithiophene‐4,8‐dione))] (PBDB‐T):IT‐M solar cell (PCE = 11.5%) is associated with the least disorder. The determined energetic disorder in part reconciles the difference in Voc between the solar cells. A reduction is observed in the nonradiative losses (ΔVnonrad) coupled with the increase of energy of CTS for the PBDB‐T:IT‐M device, which may be related to the improved balance in carrier mobilities, and partially can explain the gain in Voc. The determined radiative limit for Voc combined with the ΔVnonrad generates an excellent agreement for the Voc with the experimental values. The results suggest that minimizing the energetic disorder related to transport and CTS is critical for the mitigation of Voc losses and improvements on the device performance. 相似文献
12.
I. Gordon L. Carnel D. Van Gestel G. Beaucarne J. Poortmans 《Progress in Photovoltaics: Research and Applications》2007,15(7):575-586
A considerable cost reduction could be achieved in photovoltaics if efficient solar cells could be made from polycrystalline‐silicon (pc‐Si) thin films on inexpensive substrates. We recently showed promising solar cell results using pc‐Si layers obtained by aluminum‐induced crystallization (AIC) of amorphous silicon in combination with thermal chemical vapor deposition (CVD). To obtain highly efficient pc‐Si solar cells, however, the material quality has to be optimized and cell processes different from those applied for standard bulk‐Si solar cells have to be developed. In this work, we present the different process steps that we recently developed to enhance the efficiency of pc‐Si solar cells on alumina substrates made by AIC in combination with thermal CVD. Our present pc‐Si solar cell process yields cells in substrate configuration with efficiencies so far of up to 8·0%. Spin‐on oxides are used to smoothen the alumina substrate surface to enhance the electronic quality of the absorber layers. The cells have heterojunction emitters consisting of thin a‐Si layers that yield much higher Voc values than classical diffused emitters. Base and emitter contacts are on top of the cell in interdigitated finger patterns, leading to fill factors above 70%. The front surface of the cells is plasma textured to increase the current density. Our present pc‐Si solar cell efficiency of 8% together with the fast progression that we have made over the last few years indicate the large potential of pc‐Si solar cells based on the AIC seed layer approach. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
13.
Bofei Liu Lisha Bai Ze Chen Xiaodan Zhang Dekun Zhang Jian Ni Qian Huang Changchun Wei Jian Sun Xinliang Chen Huizhi Ren Guofu Hou Guangcai Wang Ying Zhao 《Progress in Photovoltaics: Research and Applications》2015,23(10):1313-1322
We report on improving the performance of pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells and corresponding single‐junction solar cells in this paper. Based on wet‐etching sputtered aluminum‐doped zinc oxide (ZnO:Al) substrates with optimized surface morphologies and photo‐electrical material properties, after adjusting individual single‐junction solar cells utilized in triple‐junction solar cells with various optimization techniques, we pay close attention to the optimization of tunnel recombination junctions (TRJs). By means of the optimization of individual a‐Si:H/a‐SiGe:H and a‐SiGe:H/µc‐Si:H double‐junction solar cells, we compensated for the open circuit voltage (Voc) loss at the a‐Si:H/a‐SiGe:H TRJ by adopting a p‐type µc‐Si:H layer with a low activation energy. By combining the optimized single‐junction solar cells and top/middle, middle/bottom TRJs with little electrical losses, an initial efficiency of 15.06% was achieved for pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
14.
Saeid Masudy‐Panah Goutam Kumar Dalapati K. Radhakrishnan Avishek Kumar Hui Ru Tan Elumalai Naveen Kumar Chellappan Vijila Cheng Cheh Tan DongZhi Chi 《Progress in Photovoltaics: Research and Applications》2015,23(5):637-645
Heterojunction solar cells of p‐type cupric oxide (CuO) and n‐type silicon (Si), p‐CuO/n‐Si, have been fabricated using conventional sputter and rapid thermal annealing techniques. Photovoltaic properties with an open‐circuit voltage (Voc) of 380 mV, short circuit current (Jsc) of 1.2 mA/cm2, and a photocurrent of 2.9 mA/cm2 were observed for the solar cell annealed at 300 °C for 1 min. When the annealing duration was increased, the photocurrent increased, but the Voc was found to reduce because of the degradation of interface quality. An improvement in the Voc resulting to a record value of 509 mV and Jsc of 4 mA/cm2 with a high photocurrent of ~12 mA/cm2 was achieved through interface engineering and controlling the phase transformation of CuO film. X‐ray diffraction, X‐ray photoelectron spectroscopy, and high‐resolution transmission electron microscopy analysis have been used to investigate the interface properties and crystal quality of sputter‐deposited CuO thin film. The improvement in Voc is mainly due to the enhancement of crystal quality of CuO thin film and interface properties between p‐CuO and n‐Si substrate. The enhancement of photocurrent is found to be due to the reduction of carrier recombination rate as revealed by transient photovoltage spectroscopy analysis. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
15.
Koen Vandewal Abay Gadisa Wibren D. Oosterbaan Sabine Bertho Fateme Banishoeib Ineke Van Severen Laurence Lutsen Thomas J. Cleij Dirk Vanderzande Jean V. Manca 《Advanced functional materials》2008,18(14):2064-2070
Photocurrent generation by charge‐transfer (CT) absorption is detected in a range of conjugated polymer–[6,6]‐phenyl C61 butyric acid methyl ester (PCBM) based solar cells. The low intensity CT absorption bands are observed using a highly sensitive measurement of the external quantum efficiency (EQE) spectrum by means of Fourier‐transform photocurrent spectroscopy (FTPS). The presence of these CT bands implies the formation of weak ground‐state charge‐transfer complexes in the studied polymer–fullerene blends. The effective band gap (Eg) of the material blends used in these photovoltaic devices is determined from the energetic onset of the photocurrent generated by CT absorption. It is shown that for all devices, under various preparation conditions, the open‐circuit voltage (Voc) scales linearly with Eg. The redshift of the CT band upon thermal annealing of regioregular poly(3‐hexylthiophene):PCBM and thermal aging of poly(phenylenevinylene)(PPV):PCBM photovoltaic devices correlates with the observed drop in open‐circuit voltage of high‐temperature treated versus untreated devices. Increasing the weight fraction of PCBM also results in a redshift of Eg, proportional with the observed changes in Voc for different PPV:PCBM ratios. As Eg corresponds with the effective bandgap of the material blends, a measurement of the EQE spectrum by FTPS allows us to measure this energy directly on photovoltaic devices, and makes it a valuable technique in the study of organic bulk heterojunction solar cells. 相似文献
16.
Efficient and Stable Perovskite Solar Cells via Dual Functionalization of Dopamine Semiquinone Radical with Improved Trap Passivation Capabilities
下载免费PDF全文
![点击此处可从《Advanced functional materials》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Qifan Xue Meiyue Liu Zhenchao Li Lei Yan Zhicheng Hu Jiawen Zhou Wenqiang Li Xiao‐Fang Jiang Baomin Xu Fei Huang Yuan Li Hin‐Lap Yip Yong Cao 《Advanced functional materials》2018,28(18)
Highly efficient planar heterojunction perovskite solar cells (PVSCs) with dopamine (DA) semiquinone radical modified poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) (DA‐PEDOT:PSS) as a hole transporting layer (HTL) were fabricated. A combination of characterization techniques were employed to investigate the effects of DA doping on the electron donating capability of DA‐PEDOT:PSS, perovskite film quality and charge recombination kinetics in the solar cells. Our study shows that DA doping endows the DA‐PEDOT:PSS‐modified PVSCs with a higher radical content and greater perovskite to HTL charge extraction capability. In addition, the DA doping also improves work function of the HTL, increases perovskite film crystallinity, and the amino and hydroxyl groups in DA can interact with the undercoordinated Pb atoms on the perovskite crystal, reducing charge‐recombination rate and increasing charge‐extraction efficiency. Therefore, the DA‐PEDOT:PSS‐modified solar cells outperform those based on PEDOT:PSS, increasing open‐circuit voltage (V oc) and power conversion efficiency (PCE) to 1.08 V and 18.5%, respectively. Even more importantly, the efficiency of the unencapsulated DA‐PEDOT:PSS‐based PVSCs are well retained with only 20% PCE loss after exposure to air for 250 hours. These in‐depth insights into structure and performance provide clear and novel guidelines for the design of effective HTLs to facilitate the practical application of inverted planar heterojunction PVSCs. 相似文献
17.
Do Yun Kim Erwin Guijt Ren A. C. M. M. van Swaaij Miro Zeman 《Progress in Photovoltaics: Research and Applications》2015,23(6):671-684
In this study, deposition conditions for making a‐SiOx:H are investigated systematically in order to obtain a high band gap material. We found that at given optical band gap, a‐SiOx:H with favorable opto‐electronic properties can be obtained when deposited using low CO2 flow rates and deposition pressures. We also found that a low radio frequency power density is required in order to limit the effect of ion bombardment on the material properties of i‐a‐SiOx:H and thereby the solar cell performance. In addition, by decreasing the heater temperature from 300 to 200°C when making the i‐a‐SiOx:H, the Voc can be increased. We employed optimized p‐doped and n‐doped a‐SiOx:H films into the p‐i‐n solar cells, and as a consequence, a high Voc of over 1 V and high fill factor (FF) are obtained. When depositing on texture‐etched ZnO:Al substrates, a high efficiency a‐SiOx:H single junction solar cell having a high Voc × FF product of 0.761 (Voc: 1.042 V, Jsc: 10.3 mA/cm2, FF: 0.73, efficiency: 7.83%) was obtained. The a‐SiOx:H solar cell shows comparable light degradation characteristics to standard a‐Si:H solar cells. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
18.
Koen Vandewal Zaifei Ma Jonas Bergqvist Zheng Tang Ergang Wang Patrik Henriksson Kristofer Tvingstedt Mats R. Andersson Fengling Zhang Olle Inganäs 《Advanced functional materials》2012,22(16):3480-3490
In organic solar cells based on polymer:fullerene blends, energy is lost due to electron transfer from polymer to fullerene. Minimizing the difference between the energy of the polymer exciton (ED*) and the energy of the charge transfer state (ECT) will optimize the open‐circuit voltage (Voc). In this work, this energy loss ED*‐ECT is measured directly via Fourier‐transform photocurrent spectroscopy and electroluminescence measurements. Polymer:fullerene photovoltaic devices comprising two different isoindigo containing polymers: P3TI and PTI‐1, are studied. Even though the chemical structures and the optical gaps of P3TI and PTI‐1 are similar (1.4 eV–1.5 eV), the optimized photovoltaic devices show large differences in Voc and internal quantum efficiency (IQE). For P3TI:PC71BM blends a ED*‐ECT of ~ 0.1 eV, a Voc of 0.7 V and an IQE of 87% are found. For PTI‐1:PC61BM blends an absence of sub‐gap charge transfer absorption and emission bands is found, indicating almost no energy loss in the electron transfer step. Hence a higher Voc of 0.92 V, but low IQE of 45% is obtained. Morphological studies and field dependent photoluminescence quenching indicate that the lower IQE for the PTI‐1 system is not due to a too coarse morphology, but is related to interfacial energetics. Losses between ECT and qVoc due to radiative and non‐radiative recombination are quantified for both material systems, indicating that for the PTI‐1:PC61BM material system, Voc can only be increased by decreasing the non‐radiative recombination pathways. This work demonstrates the possibility of obtaining modestly high IQE values for material systems with a small energy offset (<0.1 eV) and a high Voc. 相似文献
19.
Antonio Sánchez‐Díaz Marta Izquierdo Salvatore Filippone Nazario Martin Emilio Palomares 《Advanced functional materials》2010,20(16):2695-2700
Organic solar cells made using a blend of DPM12 and P3HT are studied. The results show that higher Voc can be obtained when using DPM12 in comparison to the usual mono‐substituted PCBM electron acceptor. Moreover, better device performances are also registered when the cells are irradiated with sun‐simulated light of 10–50 mW cm?2 intensity. Electrochemical and time‐resolved spectroscopic measurements are compared for both devices and a 100‐mV shift in the density of states (DOS) is observed for DPM12/P3HT devices with respect to PCBM/P3HT solar cells and slow polaron‐recombination dynamics are found for the DPM12/P3HT devices. These observations can be directly correlated with the observed increase in Voc, which is in contrast with previous results that correlated the higher Voc with different ideality factors obtained using dark‐diode measurements. The origin for the shift in the DOS can be correlated to the crystallinity of the blend that is influenced by the properties of the included fullerene. 相似文献
20.
Meijun Lu Ujjwal Das Stuart Bowden Steven Hegedus Robert Birkmire 《Progress in Photovoltaics: Research and Applications》2011,19(3):326-338
Interdigitated back contact silicon heterojunction (IBC‐SHJ) solar cells have the potential for high open circuit voltage (VOC) due to the surface passivation and heterojunction contacts, and high short circuit current density (JSC) due to all back contact design. Intrinsic amorphous silicon (a‐Si:H) buffer layer at the rear surface improve the surface passivation hence VOC and JSC, but degrade fill factor (FF) from an “S” shape J–V curve. Two‐dimensional (2D) simulation using “Sentaurus device” demonstrates that the low FF is related to the valence band offset (energy barrier) at the hetero‐interface. Three approaches to the buffer layer are suggested to improve the FF: (1) reduced thickness, (2) increased conductivity, and/or (3) reduced band gap. Experimental IBC‐SHJ solar cells with reduced buffer thickness (<5 nm) and increased conductivity with low boron doping significantly improves FF, consistent with simulation. However, this has only marginal effect on efficiency since JSC and VOC also decrease due to poor surface passivation. A narrow band gap a‐Si:H buffer layer improves cell efficiency to 13.5% with unoptimized passivation quality. These results demonstrate that tailoring the hetero‐interface band structure is critical for achieving high FF. Simulations predicts that efficiences >23% are possible on planar devices with optimized pitch dimensions and achievable surface passivation, and 26% with light trapping. This work provides criterion to design IBC‐SHJ solar cell structures and optimize cell performance. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献