共查询到20条相似文献,搜索用时 15 毫秒
1.
Disorder‐Induced Open‐Circuit Voltage Losses in Organic Solar Cells During Photoinduced Burn‐In
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Thomas Heumueller Timothy M. Burke William R. Mateker Isaac T. Sachs‐Quintana Koen Vandewal Christoph J. Brabec Michael D. McGehee 《Liver Transplantation》2015,5(14)
The photoinduced open‐circuit voltage (Voc) loss commonly observed in bulk heterojunction organic solar cells made from amorphous polymers is investigated. It is observed that the total charge carrier density and, importantly, the recombination dynamics are unchanged by photoinduced burn‐in. Charge extraction is used to monitor changes in the density of states (DOS) during degradation of the solar cells, and a broadening over time is observed. It is proposed that the Voc losses observed during burn‐in are caused by a redistribution of charge carriers in a broader DOS. The temperature and light intensity dependence of the Voc losses can be described with an analytical model that contains the amount of disorder broadening in a Gaussian DOS as the only fit parameter. Finally, the Voc loss in solar cells made from amorphous and crystalline polymers is compared and an increased stability observed in crystalline polymer solar cells is investigated. It is found that solar cells made from crystalline materials have a considerably higher charge carrier density than those with amorphous materials. The effects of a DOS broadening upon aging are suppressed in solar cells with crystalline materials due to their higher carrier density, making crystalline materials more stable against Voc losses during burn‐in. 相似文献
2.
Reducing Voltage Losses in Cascade Organic Solar Cells while Maintaining High External Quantum Efficiencies
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Vasileios C. Nikolis Johannes Benduhn Felix Holzmueller Fortunato Piersimoni Matthias Lau Olaf Zeika Dieter Neher Christian Koerner Donato Spoltore Koen Vandewal 《Liver Transplantation》2017,7(21)
High photon energy losses limit the open‐circuit voltage (VOC) and power conversion efficiency of organic solar cells (OSCs). In this work, an optimization route is presented which increases the VOC by reducing the interfacial area between donor (D) and acceptor (A). This optimization route concerns a cascade device architecture in which the introduction of discontinuous interlayers between alpha‐sexithiophene (α‐6T) (D) and chloroboron subnaphthalocyanine (SubNc) (A) increases the VOC of an α‐6T/SubNc/SubPc fullerene‐free cascade OSC from 0.98 V to 1.16 V. This increase of 0.18 V is attributed solely to the suppression of nonradiative recombination at the D–A interface. By accurately measuring the optical gap (Eopt) and the energy of the charge‐transfer state (ECT) of the studied OSC, a detailed analysis of the overall voltage losses is performed. Eopt – qVOC losses of 0.58 eV, which are among the lowest observed for OSCs, are obtained. Most importantly, for the VOC‐optimized devices, the low‐energy (700 nm) external quantum efficiency (EQE) peak remains high at 79%, despite a minimal driving force for charge separation of less than 10 meV. This work shows that low‐voltage losses can be combined with a high EQE in organic photovoltaic devices. 相似文献
3.
Andrej Classen Lukas Einsiedler Thomas Heumueller Arko Graf Maximilian Brohmann Felix Berger Simon Kahmann Moses Richter Gebhard J. Matt Karen Forberich Jana Zaumseil Christoph J. Brabec 《Liver Transplantation》2019,9(1)
Current state‐of‐the‐art organic solar cells (OSCs) still suffer from high losses of open‐circuit voltage (VOC). Conventional polymer:fullerene solar cells usually exhibit bandgap to VOC losses greater than 0.8 V. Here a detailed investigation of VOC is presented for solution‐processed OSCs based on (6,5) single‐walled carbon nanotube (SWCNT): [6,6]‐phenyl‐C71‐butyric acid methyl ester active layers. Considering the very small optical bandgap of only 1.22 eV of (6,5) SWCNTs, a high VOC of 0.59 V leading to a low Egap/q ? VOC = 0.63 V loss is observed. The low voltage losses are partly due to the lack of a measurable charge transfer state and partly due to the narrow absorption edge of SWCNTs. Consequently, VOC losses attributed to a broadening of the band edge are very small, resulting in VOC,SQ ? VOC,rad = 0.12 V. Interestingly, this loss is mainly caused by minor amounts of SWCNTs with smaller bandgaps as well as (6,5) SWCNT trions, all of which are experimentally well resolved employing Fourier transform photocurrent spectroscopy. In addition, the low losses due to band edge broadening, a very low voltage loss are also found due to nonradiative recombination, ΔVOC,nonrad = 0.26 V, which is exceptional for fullerene‐based OSCs. 相似文献
4.
Beyond Langevin Recombination: How Equilibrium Between Free Carriers and Charge Transfer States Determines the Open‐Circuit Voltage of Organic Solar Cells
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Organic solar cells lag behind their inorganic counterparts in efficiency due largely to low open‐circuit voltages (Voc). In this work, a comprehensive framework for understanding and improving the open‐circuit voltage of organic solar cells is developed based on equilibrium between charge transfer (CT) states and free carriers. It is first shown that the ubiquitous reduced Langevin recombination observed in organic solar cells implies equilibrium and then statistical mechanics is used to calculate the CT state population density at each voltage. This general result permits the quantitative assignment of Voc losses to a combination of interfacial energetic disorder, non‐negligible CT state binding energies, large degrees of mixing, and sub‐ns recombination at the donor/acceptor interface. To quantify the impact of energetic disorder, a new temperature‐dependent CT state absorption measurement is developed. By analyzing how the apparent CT energy varies with temperature, the interfacial disorder can be directly extracted. 63–104 meV of disorder is found in five systems, contributing 75–210 mV of Voc loss. This work provides an intuitive explanation for why qVoc is almost always 500–700 meV below the energy of the CT state and shows how the voltage can be improved. 相似文献
5.
Open‐Circuit Voltage in Organic Solar Cells: The Impacts of Donor Semicrystallinity and Coexistence of Multiple Interfacial Charge‐Transfer Bands
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Guy O. Ngongang Ndjawa Kenneth R. Graham Sonya Mollinger Di M. Wu David Hanifi Rohit Prasanna Bradley D. Rose Sukumar Dey Liyang Yu Jean‐Luc Brédas Michael D. McGehee Alberto Salleo Aram Amassian 《Liver Transplantation》2017,7(12)
In organic solar cells (OSCs), the energy of the charge‐transfer (CT) complexes at the donor–acceptor interface, E CT, determines the maximum open‐circuit voltage (V OC). The coexistence of phases with different degrees of order in the donor or the acceptor, as in blends of semi‐crystalline donors and fullerenes in bulk heterojunction layers, influences the distribution of CT states and the V OC enormously. Yet, the question of how structural heterogeneities alter CT states and the V OC is seldom addressed systematically. In this work, we combine experimental measurements of vacuum‐deposited rubrene/C60 bilayer OSCs, with varying microstructure and texture, with density functional theory calculations to determine how relative molecular orientations and extents of structural order influence E CT and V OC. We find that varying the microstructure of rubrene gives rise to CT bands with varying energies. The CT band that originates from crystalline rubrene lies up to ≈0.4 eV lower in energy compared to the one that arises from amorphous rubrene. These low‐lying CT states contribute strongly to V OC losses and result mainly from hole delocalization in aggregated rubrene. This work points to the importance of realizing interfacial structural control that prevents the formation of low E CT configurations and maximizes V OC. 相似文献
6.
Enhancement of VOC without Loss of JSC in Organic Solar Cells by Modification of Donor/Acceptor Interfaces
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Yufei Zhong Akira Tada Seiichiro Izawa Kazuhito Hashimoto Keisuke Tajima 《Liver Transplantation》2014,4(5)
Organic solar cells (OSCs) are promising low‐cost devices for generating electricity. In addition to fill factor, the short circuit current density (JSC) and the open circuit voltage (VOC) are two key factors that have critical influence on the device performance. The energy levels of the donor and acceptor materials are crucial for achieving a high JSC and VOC. However, the interfacial structures between the organic materials substantially affect the JSC and VOC through the energy of the charge transfer (CT) states and the charge separation and recombination reaction kinetics. Here, it is reported that separating the donor and acceptor layer in bilayer OSCs with a thin insulating layer increases the energy of the CT state by weakening the Coulomb interaction at the interface and this also suppresses photoinduced CT and recombination. Although these effects usually increase VOC and decrease JSC, the trade‐off is avoided by doping the insulating layer with a dye to utilize the energy transfer process. The increase in VOC without the reduction in JSC enhances the conversion efficiency of the OSCs by 30%. 相似文献
7.
Investigation of Charge Carrier Behavior in High Performance Ternary Blend Polymer Solar Cells
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Tack Ho Lee Mohammad Afsar Uddin Chengmei Zhong Seo‐Jin Ko Bright Walker Taehyo Kim Yung Jin Yoon Song Yi Park Alan J. Heeger Han Young Woo Jin Young Kim 《Liver Transplantation》2016,6(19)
This study demonstrates high‐performance, ternary‐blend polymer solar cells by modifying a binary blend bulk heterojunction (PPDT2FBT:PC71BM) with the addition of a ternary component, PPDT2CNBT. PPDT2CNBT is designed to have complementary absorption and deeper frontier energy levels compared to PPDT2FBT, while being based on the same polymeric backbone. A power conversion efficiency of 9.46% is achieved via improvements in both short‐circuit current density (JSC) and open‐circuit voltage (VOC). Interestingly, the VOC increases with increasing the PPDT2CNBT content in ternary blends. In‐depth studies using ultraviolet photoelectron spectroscopy and transient absorption spectroscopy indicate that the two polymers are not electronically homogeneous and function as discrete light harvesting species. The structural similarity between PPDT2CNBT and PPDT2FBT allows the merits of a ternary system to be fully utilized to enhance both JSC and VOC without detriment to fill‐factor via minimized disruption of semi‐crystalline morphology of binary PPDT2FBT:PC71BM blend. Further, by careful analysis, charge carrier transport in this ternary blend is clearly verified to follow parallel‐like behavior. 相似文献
8.
Trade‐Off between Trap Filling,Trap Creation,and Charge Recombination Results in Performance Increase at Ultralow Doping Levels in Bulk Heterojunction Solar Cells
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Zhengrong Shang Thomas Heumueller Rohit Prasanna George F. Burkhard Benjamin D. Naab Zhenan Bao Michael D. McGehee Alberto Salleo 《Liver Transplantation》2016,6(24)
Doping of organic bulk heterojunction solar cells has the potential to improve their power conversion efficiency (PCE). Deconvoluting the effect of doping on charge transport, recombination, and energetic disorder remains challenging. It is demonstrated that molecular doping has two competing effects: on one hand, dopant ions create additional traps while on the other hand free dopant‐induced charges fill deep states possibly leading to V OC and mobility increases. It is shown that molar dopant concentrations as low as a few parts per million can improve the PCE of organic bulk heterojunctions. Higher concentrations degrade the performance of the cells. In doped cells where PCE is observed to increase, such improvement cannot be attributed to better charge transport. Instead, the V OC increase in unannealed P3HT:PCBM cells upon doping is indeed due to trap filling, while for annealed P3HT:PCBM cells the change in V OC is related to morphology changes and dopant segregation. In PCDTBT:PC70BM cells, the enhanced PCE upon doping is explained by changes in the thickness of the active layer. This study highlights the complexity of bulk doping in organic solar cells due to the generally low doping efficiency and the constraint on doping concentrations to avoid carrier recombination and adverse morphology changes. 相似文献
9.
Saba Gharibzadeh Bahram Abdollahi Nejand Marius Jakoby Tobias Abzieher Dirk Hauschild Somayeh Moghadamzadeh Jonas A. Schwenzer Philipp Brenner Raphael Schmager Amir Abbas Haghighirad Lothar Weinhardt Uli Lemmer Bryce S. Richards Ian A. Howard Ulrich W. Paetzold 《Liver Transplantation》2019,9(21)
In this work, the authors realize stable and highly efficient wide‐bandgap perovskite solar cells that promise high power conversion efficiencies (PCE) and are likely to play a key role in next generation multi‐junction photovoltaics (PV). This work reports on wide‐bandgap (≈1.72 eV) perovskite solar cells exhibiting stable PCEs of up to 19.4% and a remarkably high open‐circuit voltage (VOC) of 1.31 V. The VOC‐to‐bandgap ratio is the highest reported for wide‐bandgap organic?inorganic hybrid perovskite solar cells and the VOC also exceeds 90% of the theoretical maximum, defined by the Shockley–Queisser limit. This advance is based on creating a hybrid 2D/3D perovskite heterostructure. By spin coating n‐butylammonium bromide on the double‐cation perovskite absorber layer, a thin 2D Ruddlesden–Popper perovskite layer of intermediate phases is formed, which mitigates nonradiative recombination in the perovskite absorber layer. As a result, VOC is enhanced by 80 mV. 相似文献
10.
Shunsuke Yamamoto Akiko Orimo Hideo Ohkita Hiroaki Benten Shinzaburo Ito 《Liver Transplantation》2012,2(2):229-237
The origin of open‐circuit voltage (VOC) was studied for polymer solar cells based on a blend of poly(3‐hexylthiophene) (P3HT) and seven fullerene derivatives with different LUMO energy levels and side chains. The temperature dependence of J–V characteristics was analyzed by an equivalent circuit model. As a result, VOC increased with the decrease in the saturation current density J0 of the device. Furthermore, J0 was dependent on the activation energy EA for J0, which is related to the HOMO–LUMO energy gap between P3HT and fullerene. Interestingly, the pre‐exponential term J00 for J0 was larger for pristine fullerenes than for substituted fullerene derivatives, suggesting that the electronic coupling between molecules also has substantial impact on VOC. This is probably because the recombination is non‐diffusion‐lmilited reaction depending on electron transfer at the P3HT/fullerene interface. In summary, the origin of VOC is ascribed not only to the relative HOMO–LUMO energy gap but also to the electronic couplings between fullerene/fullerene and polymer/fullerene. 相似文献
11.
Gongchu Liu Jianchao Jia Kai Zhang Xiao'e Jia Qingwu Yin Wenkai Zhong Li Li Fei Huang Yong Cao 《Liver Transplantation》2019,9(11)
A tandem organic solar cell (OSC) is a valid structure to widen the photon response range and suppress the transmission loss and thermalization loss. In the past few years, the development of low‐bandgap materials with broad absorption in long‐wavelength region for back subcells has attracted considerable attention. However, wide‐bandgap materials for front cells that have both high short‐circuit current density (JSC) and open‐circuit voltage (VOC) are scarce. In this work, a new fluorine‐substituted wide‐bandgap small molecule nonfullerene acceptor TfIF‐4FIC is reported, which has an optical bandgap of 1.61 eV. When PBDB‐T‐2F is selected as the donor, the device offers an extremely high VOC of 0.98 V, a high JSC of 17.6 mA cm?2, and a power conversion efficiency of 13.1%. This is the best performing acceptor with such a wide bandgap. More importantly, the energy loss in this combination is 0.63 eV. These properties ensure that PBDB‐T‐2F:TfIF‐4FIC is an ideal candidate for the fabrication of tandem OSCs. When PBDB‐T‐2F:TfIF‐4FIC and PTB7‐Th:PCDTBT:IEICO‐4F are used as the front cell and the back cell to construct tandem solar cells, a PCE of 15% is obtained, which is one of best results reported to date in the field of organic solar cells. 相似文献
12.
Mark Gruber Julia Wagner Konrad Klein Ulrich Hörmann Andreas Opitz Martin Stutzmann Wolfgang Brütting 《Liver Transplantation》2012,2(9):1100-1108
In organic photovoltaic (PV) cells, the well‐established donor‐acceptor (D/A) concept enabling photo‐induced charge transfer between two partners with suitable energy level alignment has proven extremely successful. Nevertheless, the introduction of such a heterojunction is accompanied with additional energy losses as compared to an inorganic homojunction cell, owing to the presence of a charge‐transfer (CT) state at the D/A interface. Based on the principle of detailed balance, a modified Shockley‐Queisser theory is developed including the essential effects of interfacial CT states, that allows for a quantitative assessment of the thermodynamic efficiency limits of molecular D/A solar cells. Key parameters, apart from the optical gap of the absorber material, entering the model are the energy (ECT) and relative absorption strength (αCT) of the CT state. It is demonstrated how the open‐circuit voltage (VOC) and thus the power conversion efficiency are affected by different parameter values. Furthermore, it is shown that temperature dependent device characteristics can serve to determine the CT energy, and thus the upper limit of VOC for a given D/A combination, as well as to quantify non‐radiative recombination losses. The model is applied to diindenoperylene (DIP)‐based photovoltaic devices, with open‐circuit voltages between 0.9 and 1.4 V, depending on the partner, that have recently been reported. 相似文献
13.
Terthieno[3,2‐b]Thiophene (6T) Based Low Bandgap Fused‐Ring Electron Acceptor for Highly Efficient Solar Cells with a High Short‐Circuit Current Density and Low Open‐Circuit Voltage Loss
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Xueliang Shi Jingde Chen Ke Gao Lijian Zuo Zhaoyang Yao Feng Liu Jianxin Tang Alex K.‐Y. Jen 《Liver Transplantation》2018,8(12)
A terthieno[3,2‐b]thiophene ( 6T ) based fused‐ring low bandgap electron acceptor, 6TIC , is designed and synthesized for highly efficient nonfullerene solar cells. The chemical, optical, and physical properties, device characteristics, and film morphology of 6TIC are intensively studied. 6TIC shows a narrow bandgap with band edge reaching 905 nm due to the electron‐rich π‐conjugated 6T core and reduced resonance stabilization energy. The rigid, π‐conjugated 6T also offers lower reorganization energy to facilitate very low VOC loss in the 6TIC system. The analysis of film morphology shows that PTB7‐Th and 6TIC can form crystalline domains and a bicontinuous network. These domains are enlarged when thermal annealing is applied. Consequently, the device based on PTB7‐Th : 6TIC exhibits a high power conversion efficiency (PCE) of 11.07% with a high JSC > 20 mA cm?2 and a high VOC of 0.83 V with a relatively low VOC loss (≈0.55 V). Moreover, a semitransparent solar cell based on PTB7‐Th : 6TIC exhibits a relatively high PCE (7.62%). The device can have combined high PCE and high JSC is quite rare for organic solar cells. 相似文献
14.
Temperature Dependence of Ideality Factors in Organic Solar Cells and the Relation to Radiative Efficiency
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The value and temperature dependence of the ideality factor provides essential information about the dominant recombination route in solar cells. This study presents experimental results of accurate ideality factor determination for representative organic photovoltaic cells (OPV) evaluated at different temperatures over a large current density regime. It is noted that standard dark I–V curves strongly deviate from those obtained by evaluations based on short circuit current density (J SC)–open circuit voltage (V OC) pairs. This is attributed to the applied external voltage in a dark I–V measurement not being representative of internal chemical potential, particularly at lower temperatures. Complementary electroluminescence measurements attest that the current density dependence of the ability of the solar cell to emit light is better correlated to the series resistance free ideality factor. For the studied set of OPV devices it is observed that the ideality factors are quite low, and with very weak temperature dependence. The J SC–V OC method to determine ideality factors further allows good estimates of activation energies as well as recombination current prefactors J 00. The findings imply that the principal OPV non‐radiative recombination mechanism is not recombination of free carriers with trapped carriers in an exponential density of tail states as previously reported. 相似文献
15.
Improved Open‐ Circuit Voltage in ZnO–PbSe Quantum Dot Solar Cells by Understanding and Reducing Losses Arising from the ZnO Conduction Band Tail
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Robert L. Z. Hoye Bruno Ehrler Marcus L. Böhm David Muñoz‐Rojas Rashid M. Altamimi Ahmed Y. Alyamani Yana Vaynzof Aditya Sadhanala Giorgio Ercolano Neil C. Greenham Richard H. Friend Judith L. MacManus‐Driscoll Kevin P. Musselman 《Liver Transplantation》2014,4(8)
Colloidal quantum dot solar cells (CQDSCs) are attracting growing attention owing to significant improvements in efficiency. However, even the best depleted‐heterojunction CQDSCs currently display open‐circuit voltages (VOCs) at least 0.5 V below the voltage corresponding to the bandgap. We find that the tail of states in the conduction band of the metal oxide layer can limit the achievable device efficiency. By continuously tuning the zinc oxide conduction band position via magnesium doping, we probe this critical loss pathway in ZnO–PbSe CQDSCs and optimize the energetic position of the tail of states, thereby increasing both the VOC (from 408 mV to 608 mV) and the device efficiency. 相似文献
16.
Zhenghui Luo Tao Liu Yiling Wang Guangye Zhang Rui Sun Zhangxiang Chen Cheng Zhong Jingnan Wu Yuzhong Chen Maojie Zhang Yang Zou Wei Ma He Yan Jie Min Yongfang Li Chuluo Yang 《Liver Transplantation》2019,9(18)
Generally, highly efficient organic solar cells require both a high open‐circuit voltage (VOC) and a high short‐circuit current density (JSC). Reducing the energy loss (Eloss) is an effective way to achieve a high VOC without compromising the photocurrent, which is ideal for enhancing the power conversion efficiencies (PCEs). Herein, a new chlorinated nonfullerene acceptor (ITC‐2Cl) with chlorinated thiophene‐fused end groups is developed. In comparison with the unchlorinated counterpart (ITCPTC), the introduction of Cl improves not only the electronic properties by redshifting the absorption spectra and deepening the lowest unoccupied molecular orbital energy levels, but also the molecular packing and thus thin‐film morphology. The PM6:ITC‐2Cl‐based device yields a significantly higher PCE (13.6%) with a lower Eloss (0.67 eV) than the ITCPTC‐based device (PCE of 12.3% with Eloss of 0.70 eV). More importantly, compared to the archetypal nonfullerene acceptors such as IT‐4F (PCE of 12.9% with Eloss of 0.73 eV) and IT‐4Cl (PCE of 12.7% with Eloss of 0.76 eV), the ITC‐2Cl‐based device shows a higher PCE and a lower Eloss. These results demonstrate that the chlorinated thiophene‐fused end group is a promising candidate for a high‐performance nonfullerene acceptors with low energy loss. 相似文献
17.
Comparing the Device Physics and Morphology of Polymer Solar Cells Employing Fullerenes and Non‐Fullerene Acceptors
下载免费PDF全文
![点击此处可从《Liver Transplantation》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Jason T. Bloking Tommaso Giovenzana Andrew T. Higgs Andrew J. Ponec Eric T. Hoke Koen Vandewal Sangwon Ko Zhenan Bao Alan Sellinger Michael D. McGehee 《Liver Transplantation》2014,4(12)
There is a need to find electron acceptors for organic photovoltaics that are not based on fullerene derivatives since fullerenes have a small band gap that limits the open‐circuit voltage (VOC), do not absorb strongly and are expensive. Here, a phenylimide‐based acceptor molecule, 4,7‐bis(4‐(N‐hexyl‐phthalimide)vinyl)benzo[c]1,2,5‐thiadiazole (HPI‐BT), that can be used to make solar cells with VOC values up to 1.11 V and power conversion efficiencies up to 3.7% with two thiophene polymers is demonstrated. An internal quantum efficiency of 56%, compared to 75–90% for polymer‐fullerene devices, results from less efficient separation of geminate charge pairs. While favorable energetic offsets in the polymer‐fullerene devices due to the formation of a disordered mixed phase are thought to improve charge separation, the low miscibility (<5 wt%) of HPI‐BT in polymers is hypothesized to prevent the mixed phase and energetic offsets from forming, thus reducing the driving force for charges to separate into the pure donor and acceptor phases where they can be collected. 相似文献
18.
Niva A. Ran John A. Love Michael C. Heiber Xuechen Jiao Michael P. Hughes Akchheta Karki Ming Wang Viktor V. Brus Hengbin Wang Dieter Neher Harald Ade Guillermo C. Bazan Thuc‐Quyen Nguyen 《Liver Transplantation》2018,8(5)
Organic bulk heterojunction (BHJ) solar cells require energetic offsets between the donor and acceptor to obtain high short‐circuit currents (JSC) and fill factors (FF). However, it is necessary to reduce the energetic offsets to achieve high open‐circuit voltages (VOC). Recently, reports have highlighted BHJ blends that are pushing at the accepted limits of energetic offsets necessary for high efficiency. Unfortunately, most of these BHJs have modest FF values. How the energetic offset impacts the solar cell characteristics thus remains poorly understood. Here, a comprehensive characterization of the losses in a polymer:fullerene BHJ blend, PIPCP:phenyl‐C61‐butyric acid methyl ester (PC61BM), that achieves a high VOC (0.9 V) with very low energy losses (Eloss = 0.52 eV) from the energy of absorbed photons, a respectable JSC (13 mA cm?2), but a limited FF (54%) is reported. Despite the low energetic offset, the system does not suffer from field‐dependent generation and instead it is characterized by very fast nongeminate recombination and the presence of shallow traps. The charge‐carrier losses are attributed to suboptimal morphology due to high miscibility between PIPCP and PC61BM. These results hold promise that given the appropriate morphology, the JSC, VOC, and FF can all be improved, even with very low energetic offsets. 相似文献
19.
Erin L. Ratcliff Andres Garcia Sergio A. Paniagua Sarah R. Cowan Anthony J. Giordano David S. Ginley Seth R. Marder Joseph J. Berry Dana C. Olson 《Liver Transplantation》2013,3(5):647-656
The role of work function and thermodynamic selectivity of hole collecting contacts on the origin of open circuit voltage (VOC) in bulk heterojunction organic photovoltaics is examined for poly(N‐9′‐heptadecanyl‐2,7‐carbazole‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole) (PCDTBT) and [6,6]‐phenyl‐C71 butyric acid methyl ester (PC71BM) solar cells. In the absence of a charge selective, electron blocking contact, systematic variation of the work function of the contact directly dictates the VOC, as defined by the energetic separation between the relative Fermi levels for holes and electrons, with little change in the observed dark saturation current, J0. Improving the charge selectivity of the contact through an increased barrier to electron injection from the fullerene in the blend into the hole contact results in a decreased reverse saturation current (decreased J0 and increased shunt resistance, RSH) and improved VOC. Based on these observations, we provide a set of contact design criteria for tuning the VOC in bulk heterojunction organic photovoltaics. 相似文献
20.
Pietro Caprioglio Martin Stolterfoht Christian M. Wolff Thomas Unold Bernd Rech Steve Albrecht Dieter Neher 《Liver Transplantation》2019,9(33)
Today's perovskite solar cells (PSCs) are limited mainly by their open‐circuit voltage (VOC) due to nonradiative recombination. Therefore, a comprehensive understanding of the relevant recombination pathways is needed. Here, intensity‐dependent measurements of the quasi‐Fermi level splitting (QFLS) and of the VOC on the very same devices, including pin‐type PSCs with efficiencies above 20%, are performed. It is found that the QFLS in the perovskite lies significantly below its radiative limit for all intensities but also that the VOC is generally lower than the QFLS, violating one main assumption of the Shockley‐Queisser theory. This has far‐reaching implications for the applicability of some well‐established techniques, which use the VOC as a measure of the carrier densities in the absorber. By performing drift‐diffusion simulations, the intensity dependence of the QFLS, the QFLS‐VOC offset and the ideality factor are consistently explained by trap‐assisted recombination and energetic misalignment at the interfaces. Additionally, it is found that the saturation of the VOC at high intensities is caused by insufficient contact selectivity while heating effects are of minor importance. It is concluded that the analysis of the VOC does not provide reliable conclusions of the recombination pathways and that the knowledge of the QFLS‐VOC relation is of great importance. 相似文献