Efficiency Of Silicon Solar Cells Research Articles

Efficiency enhancement of silicon solar cells covered by GeO2-PbO glasses doped with Eu3+ and TiO2 nanoparticles

An objective of the solar industry is to improve the efficiency of the light -electricity conversion process of photovoltaic solar cells. An alternative to achieve this purpose is to manage the solar spectrum that is absorbed by the solar cell in order to match it with the solar cell responsivity. It can be done, for example through the downconversion process, covering the solar cell with photonic materials that can convert photons of the UV region to photons with energy close to the band gap energy of the solar cell. This process can be observed, for example, through the UV excitation of transparent glasses with low phonon energy hosting luminescent ions with energy levels in the VIS region. The luminescence from these energetic levels can be improved siting the luminescent ions in places with low symmetry. In the present study the optical response to the solar spectrum of GeO2-PbO glasses containing Eu3+ ions and titanium dioxide nanoparticles was explored to enhance the efficiency of polycrystalline silicon solar cells. Results revealed a maximum efficiency enhancement of 15.92% for the silicon solar cell covered with GeO2-PbO glass doped with 1% of Eu2O3 and 0.5% of TiO2 heat treated for 24 h. This efficiency enhancement was attributed to the location of the Eu3+ ions in sites of low symmetry of TiO2 nanoparticles.

Photon Absorption Efficiency for Crystalline Silicon Solar Cell and Optimizing the Thickness of the Absorptive Layer

Highly efficient Crystalline silicon (c-Si) solar cells increasingly feature complex electron and hole contacts aimed at minimizing losses of electron-hole pair combination. Here, we are simulating the fate of the photon using an arbitrary variable and developing an algorithm. As the fate of the photon is a function of the absorption coefficient of the material, refractive index and thickness of the absorption layer, In this paper we developed an algorithm based on Monte Carlo Ray Tracing to track the photon packets and propose an accurate yet simple method to optimize the thickness of the absorption layer for the maximum absorption of electron-hole pair.

Green-laser-doped selective emitters with separate BBr3 diffusion processes for high-efficiency n-type silicon solar cells

Laser-doped boron selective emitters are an ideal candidate for enabling less emitter recombination, lower contact resistance and better blue response of efficient n-type silicon solar cells. However, the low boron concentration of the borosilicate glasses formed during boron diffusion processes and the implementation of ultraviolet lasers have hindered the commercialization of laser-doped boron selective emitters. In this contribution, separate BBr3 diffusion processes for green-laser-doped selective emitters are demonstrated. Laser doping processes were conducted between (1) borosilicate glass deposition and boron driving in and (2) post-oxidation, achieving the optimized laser doped selective emitter with the Rsheet,p+/Rsheet,p++ of 95.0 Ω/□/54.3 Ω/□, accompanying with the p+ profile of Nmax < 1.4× 1019 cm−3. By comparison to the homogeneous emitter with sheet resistance of 88.9 Ω/□, J0e, total of 45.3 fA/cm2 and ρc, metal of 2.9 mΩ/cm2, the employment of the optimum laser doped selective emitter has resulted in the J0e, total of 31.1 fA/cm2 and the ρc, metal of 1.0 mΩ/cm2. Finally, the improvement of simulated VOC (699.6 mV), FF (81.38%) and efficiency (23.13%) were obtained by using the optimized laser doped SEs, compared with the simulated VOC (694.5 mV), FF (81.14%) and efficiency (22.89%) of the reference. Separate BBr3 diffusion processes for green-laser-doped selective emitters demonstrate the employment of industrial green laser and boron diffusion furnace, instead of expensive ultraviolet laser and other complex boron resources, indicating a promising potential for industrial feasibility.

The influence of the pyramidal texture uniformity and process optimization on monocrystalline silicon solar cells

To improve the photoelectric conversion efficiency of monocrystalline silicon solar cells, the influence of the pyramidal texture uniformity on the defects in the monocrystalline silicon cells was analyzed by simulation, and the uniformity of the pyramidal texture was quantitatively characterized with the uniformity coefficient. The texturing process parameters were optimized by fitting and optimizing the uniformity coefficient. In the experiments herein, four groups of textured monocrystalline silicon wafers were obtained by treating them with a 1.2% sodium hydroxide (NaOH) solution for four different times. The uniformity coefficient of each monocrystalline silicon wafer group was obtained. By fitting the uniformity coefficient, we obtained the texturing process parameters corresponding to the maximum uniformity coefficient. The experimental results show that the optimized monocrystalline silicon cell achieved a pyramidal texture with a maximum uniformity coefficient. In addition, the reflectivity of the monocrystalline silicon cell reached a minimum value, and the photoelectric conversion efficiency reached a maximum value. The uniformity coefficient can not only effectively quantify the uniformity of the pyramidal texture but also effectively optimize the texturing process parameters to improve the photoelectric conversion efficiency of monocrystalline silicon cells.

Efficient tandem solar cells with solution-processed perovskite on textured crystalline silicon.

Stacking solar cells with decreasing band gaps to form tandems presents the possibility of overcoming the single-junction Shockley-Queisser limit in photovoltaics. The rapid development of solution-processed perovskites has brought perovskite single-junction efficiencies >20%. However, this process has yet to enable monolithic integration with industry-relevant textured crystalline silicon solar cells. We report tandems that combine solution-processed micrometer-thick perovskite top cells with fully textured silicon heterojunction bottom cells. To overcome the charge-collection challenges in micrometer-thick perovskites, we enhanced threefold the depletion width at the bases of silicon pyramids. Moreover, by anchoring a self-limiting passivant (1-butanethiol) on the perovskite surfaces, we enhanced the diffusion length and further suppressed phase segregation. These combined enhancements enabled an independently certified power conversion efficiency of 25.7% for perovskite-silicon tandem solar cells. These devices exhibited negligible performance loss after a 400-hour thermal stability test at 85°C and also after 400 hours under maximum power point tracking at 40°C.

Growing perovskite on textured silicon

Solar Cells Wide–band gap perovskites could boost the efficiency of silicon solar cells by forming tandem cells, but usually the perovskite must be grown on a smoothed side of the silicon cell because the material grown on the rough light-trapping side often does not fully coat the silicon surface and its rough texture is prone to phase separation. Hou et al. grew thick films of a perovskite with a band gap of ∼1.68 electron volts and used a passivant, 1-butanethiol, to limit its phase separation. The tandem cells had a certified power conversion efficiency of 25.7% and had negligible losses after 400 hours of operation. Science , this issue p. [1135][1] [1]: /lookup/doi/10.1126/science.aaz3691

Study of Nano Texturing on Multi-crystalline Silicon Solar Cells

Nano texturing has been confirmed as an effective structure to improve the efficiency of multi-crystalline silicon solar cells by reducing optical loss. In this study, nano textured solar cells are fabricated by the Reactive Ion Etching (RIE) method based on a conventional production line. Several characterization methods are employed to evaluate the morphology, minority carrier lifetime, quantum efficiency and electricity performance of both nano textured and micro textured solar cells. The results show that nano textured solar cell has the highest efficiency of 19.21 % and an average efficiency of 18.86%, which is 0.57 % higher than that of micro textured solar cells. Thus, the RIE method is an effective way to manufacture nano textured solar cells. It can demonstrably improve the photoelectric conversion efficiency of mass-produced solar cells and reduce the production cost, which is significant to the development of solar cell industry.

Development of aluminum paste with/without boron content for crystalline silicon solar cells

Improvement of aluminum alloyed p + back surface fields (p + BSF) which is an essential requirement for achieving high efficiency silicon solar cells has been an important task. One of the ways to have better quality BSFs can be to introduce screen printable aluminum pastes with boron content. Two type of pastes were developed in this work and recipes were provided in detail: screen-printable aluminum paste without boron content (B-free-Al-paste), screen-printable aluminum paste with boron content (Al-B-paste). The ingredients of the pastes were optimized and basically evaluated in terms of alloying and impurity characteristics by measurement of sheet resistances, carrier lifetimes and SIMS analysis. Carrier lifetimes of the wafers processed by Al-B-paste maintained at around 300 μs relatively higher than the wafers processed by B-free-Al-paste. P-type silicon solar cells were fabricated using developed pastes and were compared with those of the cells fabricated by commercial aluminum pastes. Best efficiency of 17.8% was achieved with totally vacuum-less cell production process and Suns-Voc analysis were also carried out for fabricated solar cells.

Layer-by-Layer Self-Assembly of Hollow Nitrogen-Doped Carbon Quantum Dots on Cationized Textured Crystalline Silicon Solar Cells for an Efficient Energy Down-Shift.

Enhancing the efficiency of the crystalline silicon solar cell (c-Si SC) by coating the energy shifting layer with quantum dots (QDs) is a recent approach to efficiently utilize the high-energy spectrum of light. Carbon QDs are an attractive candidate for such applications; however, a small Stokes shift and nonuniform coating due to high aggregation are the bottlenecks to fully utilize their potential. For this purpose, here, we propose a layer-by-layer self-assembled uniform coating of eco-friendly red-emissive hollow nitrogen-doped carbon QDs (NR-CQDs) as an efficient energy-down-shifting layer. A unique hollow and conjugated structure of NR-CQDs was designed to achieve a large Stokes shift (UV-excited red emission) with a quantum yield (QY) comparable to Cd/Pb QDs. A highly uniform coating of intrinsically negatively charged NR-CQDs on c-Si SCs was achieved by cationizing the c-Si SC by bovine serum albumin (BSA) under mildly acidic conditions. By an opposite-charge-assisted, self-assembled overlayer, the short-circuit current density (Jsc) and power-conversion efficiency were increased by 5.8%, which is attributed to the large Stokes shift (255 nm) and high QY. Blue-emissive undoped carbon QDs were synthesized for comparison with the proposed NR-CQDs to elucidate the significance of the novel proposed structure.

Development of ultra-thin doped poly-Si via LPCVD and ex-situ tube diffusion for passivated contact solar cell applications

Rear side application of polycrystalline silicon (poly-Si) passivated contacts has demonstrated very high efficiencies for single-junction monocrystalline silicon (mono-Si) solar cells. To further improve the device performance, one possible approach is to apply the passivated contact concept to the front side of the solar cell as well. The front side application requires the use of ultra-thin poly-Si layer in order to suppress parasitic absorption. Suitable ex-situ diffusion process should be developed accordingly without damaging the passivation provided by the very thin interface oxide (iOx). In this work, we prepared symmetric lifetime samples of ultra-thin poly-Si (<30 nm) via low pressure chemical vapour deposition (LPCVD) method. Then we studied and optimised the ex-situ POCl3/BBr3 diffusion doping processes. An excellent passivation quality was demonstrated with a high implied open-circuit voltage (iVoc) of up to 730 mV (on symmetric n+ poly-Si lifetime samples) and 700 mV (on symmetric p+ poly-Si lifetime samples). For possible contact formation, we capped the poly-Si with sputter-deposited ZnO:Al, which shows good opto-electrical properties and firing stability at 650 °C.

Efficient and stable thin-film crystalline silicon solar cell by introducing rotation factor in surface square pillar array grating

To obtain efficient and stable light trapping, angle rotation is introduced to form rotated square pillar array grating (SPAG) solar cells. Compared with the unpatterned stack slab and the optimized uniform SPAG cells, the maximum short-circuit current ( J sc) of the optimized rotated SPAG is increased by 78.54% and 3.21%, respectively. Moreover, besides the fact that the low-incidence angular sensitivity of J sc could be maintained, J sc of the optimized rotated SPAG will always be larger than that of the optimized uniform SPAG at any incident angle. Furthermore, when the structural parameters of the subsquare pillar slightly deviate from the optimum, the absorption only deceases slightly as well, which indicates both a high structural tolerance and a stable absorption performance. In addition, our results show not only that the proposed rotated SPAG is promising to make light trapping efficient and stable but also that introducing rotation disorders is promising for other high-absorption pseudounordered surface structures.

Photonic crystal light trapping: Beyond 30% conversion efficiency for silicon photovoltaics

The power conversion efficiency of single-junction silicon solar cells has increased only by 1.5% despite extensive efforts over the past two decades. The current world-record efficiencies of silicon solar cells, within the 25%–26.7% range, fall well below the thermodynamic limit of 32.3%. We review the recent progress in photonic crystal light-trapping architectures poised to achieve 28%–31% conversion efficiency in flexible 3–20 μm-thick, single-junction crystalline-silicon solar cells. These photonic crystals utilize wave-interference based light-trapping, enabling solar absorption well beyond the Lambertian limit in the 300–1200 nm wavelength range. Using experimentally feasible doping profiles, carrier lifetimes, surface recombination velocities, and established Auger recombination losses, we review considerations leading to the prediction of 31% efficiency in a 15 μm-thick silicon photonic crystal cell with interdigitated back-contacts. This is beyond the conversion efficiency of any single-material photovoltaic device of any thickness.

Efficient Luminescence of Sr2Si5N8:Eu2+ nanophosphor and its film applications to LED and Solar cell as a downconverter

Here we present the synthesis of the efficient nanophosphor Sr2Si5N8:Eu2+ (D50 = 144 nm) by a simple milling approach, its strong Rayleigh scattering, and its film applications to white LED and silicon solar cell as a downshifting medium. The final nanophosphor product showed the quantum efficiency comparable to the bulk phosphor which is, to our knowledge, the highest record of nitride nanophosphors. Especially the nanophosphor showed the more tail emission at the shorter-wavelength side of the emission spectrum and the faster thermal quenching with the more spectral broadening along with the temperature due to Rayleigh scattering. Also the lowering in the excitation spectrum was observed due to lower absorbance. Finally, the nanophosphor-dispersed polyvinyl alcohol (PVA) film was made, and its applications to white LED and silicon solar cell as a downshifting medium demonstrated that it gave the high color rendering property in white LED in spite of still lower luminous efficiency, and it caused the increase in efficiency of silicon solar cell.

Investigation and simulation of the effect of silver, aluminum, gold, and platinum nano-ribbons on the efficiency of amorphous silicon solar cell

In this paper, we considered a silicon solar cell with some ribbon nanoparticles including silver (Ag), aluminum (Al), gold (Au), and platinum (Pt) ribbon nanoparticles. The dimensions of nanoparticles affect the absorption and efficiency of solar cells. Here, various dimensions were examined, and the width, height, and period of the ribbon nanoparticle were taken into account. In this paper, we investigated the effect of height, width, period, and materials of ribbon nanoparticles by finite-difference time-domain method. The simulation results show that the maximum absorption was obtained equal to 12.90% by using the silver ribbon nanoparticles having width (x) of 25 nm, height (h) of 50 nm, and period (p) of 50 nm. In this case, the fill factor was obtained as 81.31%.

23.5%-efficient silicon heterojunction silicon solar cell using molybdenum oxide as hole-selective contact

Interest in silicon heterojunction solar cells is growing due to their manufacturing simplicity and record efficiencies. However, a significant limitation of these devices still stems from parasitic light absorption in the amorphous silicon layers. This can be mitigated by replacing the traditional (p) and (n) doped amorphous silicon selective layers by other materials. While promising results have been achieved using molybdenum oxide (MoOx) as a front-side hole-selective layer, charge transport mechanisms in that contact stack have remained elusive and device efficiencies below predictions. We carefully analyze the influence of the MoOx and intrinsic a-Si:H thicknesses on current-voltage properties and discuss transport and performance-loss mechanisms. In particular, we find that thinning down the MoOx and (i)a-Si:H layers (down to 4 nm and 6 nm respectively) mitigates parasitic sub-bandgap MoOx optical absorption and drastically enhances charge transport, while still providing excellent passivation and selectivity. High-resolution transmission microscopy reveals that such thin MoOx layer remains continuous and, while slightly sub-stoechiometric, exhibits a chemistry close to MoO3. A screen-printed device reaching a certified efficiency of 23.5% and a fill factor of 81.8% is demonstrated, bridging the gap with traditional Si-based contacts and demonstrating that dopant-free selective contacts can rival traditional approaches.

EFFECT OF PHOSPHOROUS/BORON DOPING PROFILE DIFFERENCES ON THE PERFORMANCE OF SILICON SOLAR CELLS

This research work was done under title “Effect of phosphorous/boron doping profile differences on the performance of silicon solar cells”. Emitter diffusion either phosphorous or boron is quite challenging in photovoltaic industry. It directly affects the emitter saturation current density and the emitter quantum efficiency of silicon solar cells. Our main objective was to make the comparison of both phosphorous and boron diffused emitters for different peak dopant concentrations in silicon solar cells. It was done by using EDNA 2 simulations. We used different parameters in EDNA 2 and simulated the high efficiency solar cells with boron as back ground and phosphorous as emitter. Then we simulated the solar cells with phosphorous as back ground and boron as emitter. We varied the peak dopant concentration of phosphorous as well boron from 1.6E+17 to 3.9E+20. The best internal quantum efficiency of emitter for phosphorous diffused emitters was 95.1 %, obtained at 1.6E19 (cm-3 ) with an effective emitter depth of 0.675 (µm). However, the best internal quantum efficiency of emitter for boron diffused emitters was 80.6 %, obtained at 3.9E19 (cm-3 ). It has an effective emitter depth of 0.732 (µm) that is greater than obtained from phosphorous diffused emitters. We concluded that the phosphorous diffused emitters have much better performance than boron diffused emitter in silicon solar cells. They have better internal quantum efficiency of emitters at lower peak dopant concentration. They have lower emitter sheet resistance with lower effective emitter depth, as also required during silicon solar cell fabrication.

Progress in perovskite based solar cells: scientific and engineering state of the art

AbstractPerovskite solar cells (PSCs) are one of the most promising photovoltaic technologies undergoing rapid developments. PSC efficiency has reached 25.2% in only seven years, which is close to the record efficiency of silicon solar cells. In addition, the use of PSCs in tandem solar cells either in the 4-terminal or monolithic configuration, can lead to a significant increase conversion efficiency. However, the stability and the scalability are the main issues that still hinder the commercialization of the perovskite technology.The present review focusses on the recent development in perovskite solar cells materials, cell architectures and fabrication methods and their effect on the conversion efficiency and stability of the devices. In addition, solutions proposed to overcome the main challenges and to make tandem solar cells are discussed.

Fabrication and degradation performance analysis of perovskite solar cells

Methyl–ammonium lead–halide perovskites are acknowledged as highly promising materials for photovoltaic applications.The popularity of these materials is due to the high efficiency of ready photovoltaic devices comparable to the efficiency of industrial silicon solar cells as well as the possibility of significant reduction in production cost. Perovskite materials have a straight and narrow bandgap, as a result of which they have a high light absorption efficiency comparable to silicon;&nbsp; and to obtain solar cells requires a thin layer of a solution obtained from solutions, which significantly reduces the production of solar cells from perovskite. The fabrication process for perovskite solar cells is rather simple and does not require high temperatures. Also, the ease of manufacturing of laboratory samples gives an opportunity to develop this technology with low capital expenditures and to join to the global research and trends in this field. The paper describes the results of fabrication and study of degradation under the influence of external factors, the atmosphere of perovskite films and solar cells obtained at a temperature of 100° C by centrifugation, which makes it possible to apply uniform films with a thickness of several nanometers to several microns easy and quickly. Key words: alternative energy, photovoltaics, perovskite solar cells.

Increasing the silicon solar cell efficiency with transition metal oxide nano-thin films as anti-reflection coatings

Herein, we report the study on RF-sputtered transition metal oxide thin films of Zinc oxide, Magnesium oxide, and Aluminum oxide as an antireflection coating on silicon-based solar cells and their influence on energy conversion. The transmission spectrum of all sputtered metal oxides was studied using a UV-visible spectrophotometer. The phase formation and microstructure analysis of these sputtered oxides were studied using glass for the destructive test along with the device. The x-ray diffraction and cross-section scanning electron microscopy of sputtered glass confirmed a single-phase structure along with nearly equal desired deposition thickness. The thicknesses of sputtered films were estimated using variable angle ellipsometry and the same was confirmed from cross-section scanning electron micrograph. The chemical composition and oxidation state of thin films deposited on glass were established from x-ray photoemission spectroscopy. The ability of a fabricated device deposited with the antireflection layer in converting photon energy to electrical energy was studied using a solar simulator under 1 sun condition. The ability to collect charge carriers of the anti-reflection coated device as a function of wavelength was also studied using quantum efficiency measurement.

Synthesis, Structural and Optical Characterization of Titanium Dioxide Doped by (Ce, Yb) Dedicated to Photonic Conversion

The synthesis of TiO2 co-doped by (Ce, Yb) rare earth couple has been realized. This couple of rare earth can convert a high-energy photon to two low energy photons to enhance the energy efficiency of silicon solar cells. The undoped, 2% Ce doped- and (2% Ce, 4% Yb) Codoped- Titanium oxide were prepared by the co-precipitation method. The Infrared spectroscopy FTIR-ATR analysis indicates a continuous visible absorption in the 750–400 cm–1 region, confirming the formation of a titanium-oxygen bond. The X-Ray Diffraction characterization showed the dominance of the rutile crystalline phase with the presence of anatase one and the calculated crystallite size is between 7 to 13 nm. The X-Ray Fluorescence confirms the insertion of the dopants while the Inductively Coupled Plasma Mass Spectrometry ICP-MS showed the ratio 2 between Ce and Yb concentration. The thermogravimetric analysis indicated that Ce/Yb doped titanium was thermally stable. The absorption in the UV-visible (200 and 1000 nm) has been improved proportionally with the dopants.