Modeling and Simulation of Heterojunction Solar Cell with Mono Crystalline Silicon

The monocrystalline silicon is a promising material that could be used in solar cells that convert light into electricity. Although the cost of ordinary silicon (Si) solar cells has decreased significantly over the past two decades, the conversion efficiency of these cells has remained relatively high. While solar cells have a great potential as a device of renewable energy, the high cost they incur per Watt continues to be a significant barrier to their widespread implementation. As a consequence, it is vital to conduct research into alternate materials that may be used in the construction of solar cells. The heterojunction solar cell (HJSC), which is based on n-type zinc oxide (n-ZnO) and p-type silicon (p-Si), is one of the numerous alternatives of the typical Si single homojunction solar cell. There are many deficiencies that can be found in the published research on n-ZnO/p-Si heterojunction solar cell. Inconsistencies in the stated value of open circuit voltage (Voc) of the solar cell are one example of deficiency. The absence of a full theoretical study to evaluate the potential of the solar cell structure is another deficiency that can be found in these researches. A lower value of experimentally obtained VOC in comparison to the theoretical prediction based on the band-gap between n-ZnO and p-Si. There needs to be more consensus among scientists regarding the optimal conditions for the growth of zinc oxide. Many software’s are available for simulating and optimizing the solar cells based on these parameters. For this purpose, in this dissertation, I provide computational results relevant to n-ZnO/p-Si HJSC to overcome deficiencies that have been identified. While modeling and simulating the potential of the solar cell structure with AFORS-HET, it is essential to consider the constraints that exist in the real world. AFORS-HET was explicitly designed to mimic the multilayer solar cell arrangement. In AFORS-HET, we can add up to seven layers for solar cell layout. By using this software, we can figure out the open circuit voltage (VOC), the short circuit current (JSC), the quantum efficiency (QE, %), the heterojunction energy band structure, and the power conversion efficiency (PCE).

Improving the UV-light stability of silicon heterojunction solar cells through plasmon-enhanced luminescence downshifting of YVO_(4):Eu^(3+),Bi^(3+)nanophosphors decorated with Ag nanoparticles

The ultraviolet(UV)light stability of silicon heterojunction(SHJ)solar cells should be addressed before large-scale production and applications.Introducing downshifting(DS)nanophosphors on top of solar cells that can convert UV light to visible light may reduce UV-induced degradation(UVID)without sacrificing the power conversion efficiency(PCE).Herein,a novel composite DS nanomaterial composed of YVO_(4):Eu^(3+),Bi^(3+)nanoparticles(NPs)and AgNPs was synthesized and introduced onto the incident light side of industrial SHJ solar cells to achieve UV shielding.The YVO_(4):Eu^(3+),Bi^(3+)NPs and Ag NPs were synthesized via a sol-gel method and a wet chemical reduction method,respectively.Then,a composite structure of the YVO_(4):Eu^(3+),Bi^(3+)NPs decorated with Ag NPs was synthesized by an ultrasonic method.The emission intensities of the YVO_(4):Eu^(3+),Bi^(3+)nanophosphors were significantly enhanced upon decoration with an appropriate amount of~20 nm Ag NPs due to the localized surface plasmon resonance(LSPR)effect.Upon the introduction of LSPR-enhanced downshifting,the SHJ solar cells exhibited an~0.54%relative decrease in PCE degradation under UV irradiation with a cumulative dose of 45 k W h compared to their counterparts,suggesting excellent potential for application in UV-light stability enhancement of solar cells or modules.

Indium–tin oxide films obtained by DC magnetron sputtering for improved Si heterojunction solar cell applications

The indium-tin oxide （ITO） film as the antireflection layer and front electrodes is of key importance to obtaining high efficiency Si heterojunction （HJ） solar cells. To obtain high transmittance and low resistivity ITO films by direct-current （DC） magnetron sputtering, we studied the impacts of the ITO film deposition conditions, such as the oxygen flow rate, pressure, and sputter power, on the electrical and optical properties of the ITO films. ITO films of resistivity of 4 x 10-4 ~.m and average transmittance of 89% in the wavelength range of 380-780 nm were obtained under the optimized conditions： oxygen flow rate of 0.1 sccm, pressure of 0.8 Pa, and sputtering power of 110 W. These ITO films were used to fabricate the single-side HJ solar cell without an intrinsic a-Si：H layer. However, the best HJ solar cell was fabricated with a lower sputtering power of 95 W, which had an efficiency of 11.47%, an open circuit voltage （Voc） of 0.626 V, a filling factor （FF） of 0.50, and a short circuit current density （Jsc） of 36.4 mA/cm2. The decrease in the performance of the solar cell fabricated with high sputtering power of 110 W is attributed to the ion bombardment to the emitter. The Voc was improved to 0.673 V when a 5 nm thick intrinsic a-Si：H layer was inserted between the （p） a-Si：H and （n） c-Si layer. The higher Voc of 0.673 V for the single-side HJ solar cell implies the excellent c-Si surface passivation by a-Si：H.

Influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H(n)/c-Si(p)heterojunction solar cells

P-type silicon heterojunction（SHJ） solar cells with a-SiC：H（n） emitters were studied by numerical computer simulation in this paper. The influence of interface states, conduction band offset, and front contact on the performance of a-SiC：H（n）/c-Si（p） SHJ solar cells was investigated systematically. It is shown that the open circuit voltage（Voc） and fill factor（F F） are very sensitive to these parameters. In addition, by analyzing equilibrium energy band diagram and electric field distribution, the influence mechanisms that interface states, conduction band offset, and front contact impact on the carrier transport, interface recombination and cell performance were studied in detail. Finally, the optimum parameters for the a-SiC：H（n）/c-Si（p） SHJ solar cells were provided. By employing these optimum parameters, the efficiency of SHJ solar cell based on p-type c-Si was significantly improved.

Effect of emitter layer doping concentration on the performance of a silicon thin film heterojunction solar cell

A novel type of n/i/i/p heterojunction solar cell with a-Si：H（15 nm）/a-Si：H（10 nm）/epitaxial c-Si（47 p.m）/epitaxial c-Si（3 um） structure is fabricated by using the layer transfer technique, and the emitter layer is deposited by hot wire chemical vapour deposition. The effect of the doping concentration of the emitter layer Sd （Sd=PH3/（PH3 ＋SiH4＋H2）） on the performance of the solar cell is studied by means of current density-voltage and external quantum efficiency. The results show that the conversion efficiency of the solar cell first increases to a maximum value and then decreases with Sd increasing from 0.1% to 0.4%. The best performance of the solar cell is obtained at Sd = 0.2% with an open circuit voltage of 534 mV, a short circuit current density of 23.35 mA/cm2, a fill factor of 63.3%, and a conversion efficiency of 7.9%.

Sub-stochiometric MoO_(x) by radio-frequency magnetron sputtering as hole-selective passivating contacts for silicon heterojunction solar cells

The silicon heterojunction(SHJ)solar cell has long been considered as one of the most promising candidates for the next-generation PV market.Transition metal oxides(TMOs)show good carrier selectivity when combined with c-Si solar cells.This has led to the rapid demonstration of the remarkable potential of TMOs(especially MoO_(x))with high work function to replace the p-type a-Si:H emitting layer.MoO_(x) can induce a strong inversion layer on the interface of n-type c-Si,which is beneficial to the extraction and conduction of holes.In this paper,the radio-frequency(RF)magnetron sputtering is used to deposit MoO_(x) films.The optical,electrical and structural properties of MoO_(x) films are measured and analyzed,with focus on the inherent compositions and work function.Then the MoO_(x) films are applied into SHJ solar cells.When the MoO_(x) works as a buffer layer between ITO/p-a-Si:H interface in the reference SHJ solar cell,a conversion efficiency of 19.1%can be obtained.When the MoOx is used as a hole transport layer(HTL),the device indicates a desirable conversion efficiency of 17.5%.To the best of our knowledge,this current efficiency is the highest one for the MoO_(x) film as HTL by RF sputtering.

Orthogonal Solubility in Fully Conjugated Donor-Acceptor Block Copolymers： Compatibilizers for Polymer/Fullerene Bulk-Heterojunction Solar Cells

Donor-acceptor （D-A） type fully conjugated block copolymer systems have been rarely reported due to the challenges in synthetic approaches to prepare well-defined low-polydispersity products. In this work, fully conjugated block copolymers are synthesized in a one-pot reaction through Stille coupling polycondensation, by utilizing the end-functional polymer copolymerization method. End-functional P3HT are copolymerized with AA （2,7-dihromo-9-（heptadecan-9-yl）-9H- carbazole） and BB （4,7-bis（5-（trimethylstannyl）thiophen-2-yl）benzo[c][1,2,5]thiadiazole, TBT） type monomers, respectively. The orthogonal solubility between the very soluble P3HT donor and the insoluble PCDTBT acceptor block improves the purity of block copolymers as well as distinct nano-scale phase-separation compared with other reports on miscibility of donor and acceptor polymer block. Further purification via preparative GPC is carried out to remove the excess of unreacted P3HT and free PCDTBT as well as to achieve low polydispersity of block copolymers. The chemical structure of the P3HT- b-PCDTBT block copolymers are verified via IH-NMR, and further confirmed by FTIR spectra. The block copolymer shows broad absorption and moderate optical band gap of 1.8 eV. Furthermore, the fully conjugated block copolymer films exhibit significant fine structures, much smoother film morphology compared to P3HT/PCDTBT polymer blends. By adding a small amount of block copolymer P3HT-b-PCDTBT as a compatibilizer into the bulk-heterojunction of P3HT：PC61BM blends, polymer solar ceils with an 8% increase of short circuit current （Jse） and 10% increase of power conversion efficiency （PCE） are achieved owing to the improvement of the active-layer film morphology. To the best of our knowledge, this is the first report on donor-acceptor type fully conjugated block copolymer as an effective ternary additive in polymer： fullerene bulk heterojunction solar cells.

Simulation of a high-efficiency silicon-based heterojunction solar cell

The basic parameters of a-Si：H/c-Si heterojunction solar cells, such as layer thickness, doping concen- tration, a-Si：H/c-Si interface defect density, and the work functions of the transparent conducting oxide （TCO） and back surface field （BSF） layer, are crucial factors that influence the carrier transport properties and the efficiency of the solar cells. The correlations between the carrier transport properties and these parameters and the performance of a-Si：H/c-Si heterojunction solar cells were investigated using the AFORS-HET program. Through the analysis and optimization of a TCO/n-a-Si：H/i-a-Si：H/p-c-Si/p＋-a-Si：H/Ag solar cell, a photoelectric conversion efficiency of 27.07% （Voc： 749 mV, Jsc： 42.86 mA/cm2, FF： 84.33%） was obtained through simulation. An in-depth understanding of the transport properties can help to improve the efficiency of a-Si：H/c-Si heterojunction solar cells, and provide useful guidance for actual heterojunction with intrinsic thin layer （HIT） solar cell manufacturing.

Plasma enhanced chemical vapor deposition of excellent a-Si：H passivation layers for a-Si：H/c-Si heterojunction solar cells at high pressure and high power

The intrinsic a-Si：H passivation layer inserted between the doped a-Si：H layer and the c-Si substrate is very crucial for improving the performance of the a-Si：H/c- Si heterojunction （SHJ） solar cell. The passivation performance of the a-Si：H layer is strongly dependent on its microstructure. Usually, the compact a-Si：H deposited near the transition from the amorphous phase to the nanocrystalline phase by plasma enhanced chemical vapor deposition （PECVD） can provide excellent passivation. However, at the low deposition pressure and low deposition power, such an a-Si：H layer can be only prepared in a narrow region. The deposition condition must be controlled very carefully. In this paper, intrinsic a- Si：H layers were prepared on n-type Cz c-Si substrates by 27.12 MHz PECVD at a high deposition pressure and high deposition power. The corresponding passivation perfor- mance on c-Si was investigated by minority carrier lifetime measurement. It was found that an excellent a-Si：H passivation layer could be obtained in a very wide deposition pressure and power region. Such wide process window would be very beneficial for improving the uniformity and the yield for the solar cell fabrication. The a-Si：H layer microstructure was further investigated by Raman and Fourier transform infrared （FTIR） spectro-scopy characterization. The correlation between the microstructure and the passivation performance was revealed. According to the above findings, the a-Si：H passivation performance was optimized more elaborately. Finally, a large-area SHJ solar cell with an efficiency of 22.25% was fabricated on the commercial 156 mm pseudo-square n-type Cz c-Si substrate with the opencircuit voltage （Voc） of up to 0.732 V.

Simulation approach for optimization of ZnO/c-WSe2 heterojunction solar cells

Taking into account defect density in WSe2,interface recombination between ZnO and WSe2,we presented a simulation study of ZnO/crystalline WSe2 heterojunction（HJ） solar cell using wxAMPS simulation software.The optimal conversion efficiency 39.07%for n-ZnO/p-c-WSe2 HJ solar cell can be realized without considering the impact of defects.High defect density（〉 1.0×10^11cm^-2） in c-WSe2 and large trap cross-section（〉 1.0×10^-10cm^2） have serious impact on solar cell efficiency.A thin p-WSe2 layer is intentionally inserted between ZnO layer and c-WSe2 to investigate the effect of the interface recombination.The interface properties are very crucial to the performance of ZnO/c-WSe2 HJ solar cell.The affinity of ZnO value range between 3.7-4.5 eV gives the best conversion efficiency.

Simulation study of the losses and influences of geminate and bimolecular recombination on the performances of bulk heterojunction organic solar cells

We use the method of device simulation to study the losses and influences of geminate and bimolecular recombinations on the performances and properties of the bulk heterojunction organic solar cells. We find that a fraction of electrons（holes）in the device are collected by anode（cathode）. The direction of the corresponding current is opposite to the direction of photocurrent. And the current density increases with the bias increasing but decreases as bimolecular recombination（BR）or geminate recombination（GR） intensity increases. The maximum power, short circuit current, and fill factor display a stronger dependence on GR than on BR. While the influences of GR and BR on open circuit voltage are about the same.Our studies shed a new light on the loss mechanism and may provide a new way of improving the efficiency of bulk heterojunction organic solar cells.

Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

Polymer solar cells （PSCs） based on poly（3-hexylthiophene） （P3HT） and [6,6]-phenyl-C61-butyric acid methyl ester （PCBM） are fabricated by using 1,8-diiodooctane （DIO） as a solvent additive to control the doping density of the PSCs. It is shown that the processing of DIO does not change the doping density of the P3HT phase, while it causes a dramatic reduction of the doping density of the PCBM phase, which decreases the doping density of the whole blend layer from 3.7 × 10^16 cm-3 to 1.2 ×10^16 cm-3. The reduction of the doping density in the PCBM phase originates from the increasing crystallinity of PCBM with DIO addition, and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.

Application of TiO_2 with different structures in solar cells

The application of TiO2-based devices is mainly dependent on their crystalline structure, morphology, size, and exposed facets. Two kinds of TiO2 with different structures, namely TiO2 pompons and TiO2 nanotubes, have been prepared by the hydrothermal method. TiO2 with different structures is characterized by scanning electron microscopy （SEM）, X-ray diffraction （XRD）, and Brunauer Emmett-Teller （BET） surface area analysis. Solar cells based on poly（3-hexylthiophene） （P3HT） and TiO2 with different structures are fabricated. In the device ITO/TiO2/P3HT/Au, the P3HT is designed to act as the electron donor, and TiO2 pompons and TiO2 nanotubes act as the electron acceptor. The effects of the TiO2 structure on the performance of hybrid heterojunction solar cells are investigated. The device with TiO2 pompons has an open circuit voltage （Voc） of 0.51 V, a short circuit current （Jsc） of 0.21 mA/cm2, and a fill factor （FF） of 28.3%. Another device with TiO2 nanotubes has a Voc of 0.5 V, Jsc of 0.27 mA/cm2, and FF of 28.4%. The results indicate that the TiO2 nanotubes with a unidimensional structure have better carrier transport and light absorption properties than TiO2 pompons. Consequently, the solar cell based on TiO2 nanotubes has a better performance.

Influence of small-molecule material on performance of polymer solar cells based on MEH-PPV:PCBM blend

In this work, the influence of a small-molecule material, tris（8-hydroxyquinoline） aluminum （Alq3）, on bulk heterojunction （BHJ） polymer solar cells （PSCs） is investigated in devices based on the blend of poly（2-methoxy-5-（2- ethylhexyloxy）-1,4-phenylenevinylene） （MEH-PPV） and [6,6]-phenyl-C61-butyric acid methyl ester （PCBM）. By doping Alq3 into MEH-PPV：PCBM solution, the number of MEH-PPV excitons can be effectively increased due to the energy transfer from Alq3 to MEH-PPV, which probably induces the increase of photocurrent generated by excitons dissociation. However, the low carrier mobility of Alq3 is detrimental to the efficient charge transport, thereby blocking the charge collection by the respective electrodes. The balance between photon absorption and charge transport in the active layer plays a key role in the performance of PSCs. For the case of 5 wt.% Alq3 doping, the device performance is deteriorated rather than improved as compared with that of the undoped device. On the other hand, we adopt Alq3 as a buffer layer instead of commonly used LiF. All the photovoltaic parameters are improved, yielding an 80% increase in power conversion efficiency （PCE） at the optimum thickness （1 nm） as compared with that of the device without any buffer layer. Even for the 5 wt.% Alq3 doped device, the PCE has a slight enhancement compared with that of the standard device after modification with 1 nm （or 2 nm） thermally evaporated Alq3. The performance deterioration of Alq3-doped devices can be explained by the low solubility of Alq3, which probably deteriorates the bicontinuous D-A network morphology; while the performance improvement of the devices with Alq3 as a buffer layer is attributed to the increased light harvesting, as well as blocking the hole leakage from MEH-PPV to the aluminum （Al） electrode due to the lower highest occupied molecular orbital （HOMO） level of Alq3 compared with that of MEH-PPV.

Designing novel thin film polycrystalline solar cells for high efficiency:sandwich CIGS and heterojunction perovskite

Heterojunction and sandwich architectures are two new-type structures with great potential for solar cells.Specifically,the heterojunction structure possesses the advantages of efficient charge separation but suffers from band offset and large interface recombination;the sandwich configuration is favorable for transferring carriers but requires complex fabrication process.Here,we have designed two thin-film polycrystalline solar cells with novel structures：sandwich CIGS and heterojunction perovskite,referring to the advantages of the architectures of sandwich perovskite（standard）and heterojunction CIGS（standard）solar cells,respectively.A reliable simulation software wxAMPS is used to investigate their inherent characteristics with variation of the thickness and doping density of absorber layer.The results reveal that sandwich CIGS solar cell is able to exhibit an optimized efficiency of 20.7%,which is much higher than the standard heterojunction CIGS structure（18.48%）.The heterojunction perovskite solar cell can be more efficient employing thick and doped perovskite films（16.9%）than these typically utilizing thin and weak-doping/intrinsic perovskite films（9.6%）.This concept of structure modulation proves to be useful and can be applicable for other solar cells.

Enhanced Power Conversion Efficiency in Bulk Heterojunction Polymer Solar Cells Through Dual-Interface Morphology Modification

Efficient bulk heterojunction（BHJ） polymer solar cells with a poly（3,4-ethylenedioxythiophene）：poly（styrenesulfonate） hole transfer layer（HTL） were fabricated via controlling the spin coating speed of the HTL solution on a particular fluorinated tin oxide substrates of a high roughness.It shows that the functions of the photovoltaic devices increase with the increase of the HTL surface roughness.Then,an imprinting technique was employed to transfer a suitable pattern of nanostructure arrays to the surface of active layers.At the optimized spin coating speed,the photovoltaic devices exhibited a 28.4% increase in efficiency after this imprinting treatment compared with that of nonimprinted photovoltaic devices.It is mainly attributed to the achievement of high interface areas between active layers and electrodes,which not only increases optical absorption by scattering but also facilitates charge carrier collection.

Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications

The application of molybdenum oxide in the photovoltaic field is gaining traction as this material can be deployed in doping-free heterojunction solar cells in the role of hole selective contact.For modeling-based optimization of such contact,knowledge of the molybdenum oxide defect density of states(DOS)is crucial.In this paper,we report a method to extract the defect density through nondestructive optical measures,including the contribution given by small polaron optical transitions.The presence of defects related to oxygen-vacancy and of polaron is supported by the results of our opto-electrical characterizations along with the evaluation of previous observations.As part of the study,molybdenum oxide samples have been evaluated after post-deposition thermal treatments.Quantitative results are in agreement with the result of density functional theory showing the presence of a defect band fixed at 1.1 eV below the conduction band edge of the oxide.Moreover,the distribution of defects is affected by post-deposition treatment.

Conjugated Polymers as Hole Transporting Materials for Solar Cells

In principle,conjugated polymers can work as electron donors and thus as low-cost p-type organic semiconductors to transport holes in photovoltaic devices.With the booming interests in high-efficiency and low-cost solar cells to tackle global climate change and energy shortage,hole transporting materials(HTMs)based on conjugated polymers have received increasing attention in the past decade.In this perspective,recent advances in HTMs for a range of photovoltaic devices including dye-sensitized solar cells(DSSCs),perovskite solar cells(PSCs),and silicon(Si)/organic heterojunction solar cells(HSCs)are summarized and perspectives on their future development are also presented.

Cu_2O-based solar cells using oxide semiconductors

We describe significant improvements of the photovoltaic properties that were achieved in Al-doped ZnO（AZO）/n-type oxide semiconductor/p-type Cu_2O heterojunction solar cells fabricated using p-type Cu_2O sheets prepared by thermally oxidizing Cu sheets. The multicomponent oxide thin film used as the n-type semiconductor layer was prepared with various chemical compositions on non-intentionally heated Cu_2O sheets under various deposition conditions using a pulsed laser deposition method. In Cu_2O-based heterojunction solar cells fabricated using various ternary compounds as the n-type oxide thin-film layer, the best photovoltaic performance was obtained with an n-ZnGa_2O_4 thin-film layer. In most of the Cu_2O-based heterojunction solar cells using multicomponent oxides composed of combinations of various binary compounds, the obtained photovoltaic properties changed gradually as the chemical composition was varied. However, with the ZnO–MgO and Ga_2O_3–Al_2O_3systems, higher conversion efficiencies（á/ as well as a high open circuit voltage（Voc/ were obtained by using a relatively small amount of MgO or Al_2O_3, e.g.,（ZnO）0：91–（MgO）0：09 and（Ga_2O_3/0：975–（Al_2O_3/0：025, respectively. When Cu_2O-based heterojunction solar cells were fabricated using Al_2O_3–Ga_2O_3–MgO–ZnO（AGMZO）multicomponent oxide thin films deposited with metal atomic ratios of 10, 60, 10 and 20 at.% for the Al, Ga, Mg and Zn, respectively, a high Vocof 0.98 V and an á of 4.82% were obtained. In addition, an enhanced á and an improved fill factor could be achieved in AZO/n-type multicomponent oxide/p-type Cu_2O heterojunction solar cells fabricated using Na-doped Cu_2O（Cu_2O：Na） sheets that featured a resistivity controlled by optimizing the post-annealing temperature and duration. Consequently, an á of 6.25% and a Vocof 0.84 V were obtained in a Mg F2/AZO/n-（Ga_2O_3–Al_2O_3//p-Cu_2O：Na heterojunction solar cell fabricated using a Cu_2O：Na sheet with a resistivity of approximately 10 cm and a（Ga_（0：975）A_（l0：025）/2O3 thin film with a thickness of approximately 60 nm.In addition, a Vocof 0.96 V and an á of 5.4% were obtained in a Mg F_2/AZO/n-AGMZO/p-Cu_2O：Na heterojunction solar cell.

D-A structural protean small molecule donor materials for solution-processed organic solar cells

Under the synergistic effect of molecular design and devices engineering, small molecular organic solar cells have presented an unstoppable tendency for rapid development with putting forward donor- acceptor （D-A） structures. Up to now, the highest power conversion efficiency of small molecules has exceeded 11%, comparable to that of polymers. In this review, we summarize the high performance small molecule donors in various classes of typical donor-acceptor （D-A） structures and discuss their relationships briefly.