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Room temperature photoluminescence (PL) and intensity dependent PL measurements were used as a tool to investigate alkali treatment (KF and RbF) of thin (< 500 nm) single-stage absorber layers and compared with similar 3-stage samples. Single-stage absorber layers have a clear distinguishable PL peak below the band gap, which is absent in 3-stage absorber layers. We attribute this peak to a defect band arising due to the planar defects and the small grains. We find that this low energy peak can be largely reduced with alkali treatment, leading to similar decay times and PL yield as thin 3 stage samples. This work received funding from the European Union’s H2020 research and innovation program under grant agreement No. 715027

We present a novel process sequence to simplify the rear-side patterning of the silicon heterojunction interdigitated back contact (HJ IBC) cells. In this approach, interdigitated strips of a-Si:H (i/p(+)) hole contact and a-Si:H (i/n(+)) electron contact are achieved by partially etching a blanket a-Si:H (i/p(+)) stack through an SiOx hard mask to remove only the p(+) a-Si:H layer and replace it with an n(+) a-Si:H layer, thereby switching from a hole contact to an electron contact in situ, without having to remove the entire passivation. This eliminates the ex situ wet clean after dry etching and also prevents re-exposure of the crystalline silicon surface during rear-side processing. Using a well-controlled process, high-quality passivation is maintained throughout the rear-side process sequence leading to high open-circuit voltages (V-OC). A slightly higher contact resistance at the electron contact leads to a slightly higher fill factor (FF) loss due to series resistance for cells from the partial etch route, but the FF loss due to J(02)-type recombination is lower, compared with reference cells. As a result, the best cell from the partial etch route has an efficiency of 22.9% and a V-OC of 729 mV, nearly identical to the best reference cell, demonstrating that the developed partial etch process can be successfully implemented to achieve cell performance comparable with reference, but with a simpler, cheaper, and faster process sequence. European Commission's Horizon 2020Framework Programme, Grant/Award Num-ber: 727523; IIAP‐SiPV; Kuwait Foundationfor the Advancement of Sciences, Grant/Award Number: P115‐15EE‐01

To guarantee a long lifetime of perovskite-based photovoltaics, the selected materials need to survive relatively hightemperature stress during the solar cell operation. Highly efficient ni-p perovskite solar cells (PSCs) often degrade at high operational temperatures due to morphological instability of the hole transport material 2,2',7,7'-tetrakis (N,N-di-p-methoxyphenyl-amine)9,9'-spirobifluorene (Spiro-OMeTAD). We discovered that the detrimental large-domain spiro-OMeTAD crystallization is caused by the simultaneous presence of tert-butylpyridine (tBP) additive and gold (Au) as a capping layer. Based on this discovery and our understanding, we demonstrated facile strategies that successfully stabilize the amorphous phase of spiro-OMeTAD film. As a result, the thermal stability of n- i-p PSCs is largely improved. After the spiro-OMeTAD films in the PSCs were stressed for 1032 h at 85 degrees C in the dark in nitrogen environment, reference PSCs retained only 22% of their initial average power conversion efficiency (PCE), while the best target PSCs retained 85% relative average PCE. Our work suggests facile ways to realize efficient and thermally stable spiro-OMeTAD containing n-i-p PSCs. European Union's H2020 Program for research, technological development, and demonstration [764047]; Kuwait Foundation for the Advancement of Sciences [CN18-15EE-01]; Research Foundation.Flanders (FWO)[G031416N]

With the growing competition of utility-scale photovoltaic (PV) plants to provide electricity to the grid, accurate energy yield simulation is becoming essential. Apart from irradiance, forced convection can have an equally significant impact on solar cell temperature, which in turn affects the power output, hence the energy yield. As a consequence, the wind must be taken into account for an accurate estimation of PV installations' energy yield. However, no earlier studies have systematically investigated the impact of wind on precise energy yield simulation. In this study, we investigate how sensitive is PV module's output to forced convection. First, we reveal a significant deviation between the simulated PV module's energy yield and cell temperature compared to experimental results in case dynamic wind effects are neglected. Secondly, for controlled incremental forced convection with a steady state scenario, we show that for higher wind speed the change of PV module's cell temperature and power output is small with different forced convection. Whereas, for the low wind speed, small changes of forced convection imply a larger variation of the PV module's cell temperature and power output. This shows that for high wind speed region energy yield estimation is less sensitive on modelling errors. Whereas for the low wind speed region it is highly sensitive. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 751159. Chowdhury, MG (corresponding author), Katholieke Univ Leuven, ELECTA ESAT MICAS, Kasteelpk Arenberg 10, B-3001 Leuven, Belgium ; IMEC, Kapeldreef 75, B-3001 Heverlee, Belgium ; Imec Partner EnergyVille, Thor Pk 8320, B-3600 Genk, Belgium.

Hybrid metal-halide perovskite-based thin-film photovoltaics (PVs) have the potential to become the next generation of commercialized PV technology with certified power conversion efficiencies reaching 24% on devices having 0.1 cm(2) area. Recent efforts in upscaling this technology result in an efficiency of 12.6% for 354 cm(2) modules. However, upscaling loss for perovskite-based PVs is higher than for any other PV technology. In this study, upscaling losses of devices with aperture area 0.1, 4, and 100 cm(2) are investigated, with a focus on layer inhomogeneities. Electroluminescence, dark lock-in thermography, microphotoluminescence spectroscopy, and electron spectroscopy are used to analyze and group layer inhomogeneities with a minimal size of 10 mu m and to compare loss mechanisms for radial and linear deposition techniques. Analysis results help to identify current processing pitfalls, where understanding and control of perovskite crystal formation plays the crucial role.

This paper proposes a kerfless wafer structure with built-in p-n junctions in n-type silicon wafers grown using Crystal Solar's high throughput epitaxy technology. Compared with a conventional p-type emitter by boron diffusion, ion implantation, or epitaxy, the built-in p-type emitter has a reduced and uniform doping concentration and increased thickness. The epitaxially grown wafers and conventional Czochralski (CZ) n-type wafers were processed into solar cells. A best efficiency of 22.5% with epitaxially grown wafers was achieved, with a 6 mV gain in open-circuit voltage, suggesting a high wafer quality and superiority of the deep epitaxial emitter over a standard boron-diffused emitter. Substrate reuse associated with the kerfless epitaxy technology is studied as well, with respect to its impact on solar cell efficiency. The data suggest no degradation in cell efficiency due to substrate reuse.

Partial shading causes power loss in a photovoltaic module by inducing a power mismatch within the module. This power loss can be significant in building-applied and building-integrated photovoltaic installations. Given the often repetitive nature of shade profiles in such applications, we propose to employ non-reconfigurable or static configurations. We use our simulation tool to precompute static configurations, apply shading scenarios, such as a chimney or tree shade, and make a comparison between the energy yields of different static configurations, which includes that of a conventional module. We then identify the configuration characteristics that consistently yield a higher energy. Copyright © 2016 John Wiley & Sons, Ltd.

The influence of the plasma ignition condition during PECVD deposition from a silane/hydrogen mixture on the amorphous silicon passivation of crystalline silicon surface is investigated. The changes in this process step mainly consist in varying the power density for very brief durations in between 1 s and 3 s. We find that the ignition phase contributes significantly in the film growth, especially in the a-Si:H/c-Si interface formation. In particular, the deposition rate increases with ignition power density. TEM cross-section inspection presents a rougher a-Si:H/c-Si interface with higher plasma power and thus, a tendency for nano-clusters formation caused by the crystalline nature of the substrate. In-situ plasma diagnostics reveal the gradual raise up of I Ha*/ I SiH* with the power density leading to worse SiH* abstraction to the surface. Whereas, time-resolved optical emission spectroscopy explains the possible recombination mechanism in the plasma due to higher-silane related reactive species (HSRS) formation via polymerization reactions. Our results point out that the ignition conditions with a rather low power for longer time give the best passivation, resulting an effective lifetime up to 9 ms.

In order to reduce the material cost for silicon solar cells, several research groups are investigating methods to minimize the silicon consumption for making monocrystalline silicon wafers. One promising approach is deposition of an epitaxial layer on porous silicon, followed by detachment of the layer. This contribution discusses improvements in the epitaxial wafer fabrication by optimization of the porosification process. The introduction of a layered porous silicon structure allows to independently improve both epitaxial layer quality and detachment yield. In this way, we have managed to obtain 100µm thick silicon wafers with effective lifetimes up to 1.3ms, and 40µm thick wafers with effective lifetimes up to 700µs. We will also review the current status of the process development for solar cells made on thin wafers. Two approaches are presented. In the first approach, heterojunction solar cells are fabricated on freestanding epitaxial wafers of 40µm thickness. In the second approach, high efficiency (21%) heterojunction back-contacted cells are fabricated on wafers that are bonded to a glass superstrate. Challenges for device processing and limitations in cell performance are discussed.

We report on a perovskite solar module with an aperture area of 4 cm2 and geometrical fill factor of 91%. The module exhibits an aperture area power conversion efficiency (PCE) of 13.6% from a current–voltage scan and 12.6% after 5 min of maximum power point tracking. High PCE originates in pinhole-free perovskite films made with a precursor combination of Pb(CH3CO2)2·3H2O, PbCl2, and CH3NH3I.

Ultrathin single- and three-stage Cu(In,Ga)Se-2 absorber layers were analyzed with room temperature photoluminescence (PL) spectra. An anomalous blueshift was observed upon increasing carrier injection for both samples. This blueshift was attributed to the presence of bandgap fluctuations that are of the same order as the minority carrier diffusion length. From time resolved measurements, a diffusion length of a few 100nms was deduced. The single-stage spectrum consists of two peaks, and the sample was, therefore, also analyzed by hyperspectral imaging, providing lateral PL and reflectance data with 1 mu m resolution. Marginal variations were observed in the PL yield and spectra. This homogeneity could again be attributed to an intermediate scale of the bandgap fluctuation with an upper limit of 1 mu m for the scale of the lateral bandgap fluctuations. The two peaks in the PL spectra of the single-stage sample could be attributed to interference, and correction methods were applied. The bandgap fluctuations were extracted for the three-stage and single-stage sample and were 45meV and 72 +/- 3meV, respectively. It is suggested that this difference is attributed to the smaller grains and larger amount of grain boundaries in the single-stage sample. This work received funding from the European Union's H2020 Research and Innovation Program under Grant Agreement No. 715027. We acknowledge Photon etc. and Professor Delphine Bouilly's research group from IRIC for the hyperspectral measurements and Erik Spaans for the python program.

In ultrathin Cu(In,Ga)Se-2(CIGS) film solar cells, the CdS/CIGS interface may become one of the limiting factors for efficiency. The first step toward reducing the impact of this problem could be a surface treatment process to improve the quality of the front interface. The purpose of this study is to have a better understanding of the effect of wet chemical surface treatment, using ammonium sulfide ((NH4)(2)S), on CIGS thin film layers with different Cu/(Ga + In) (CGI) ratios. Herein, photoluminescence (PL) and time-resolved PL (TRPL) studies are conducted on bare CIGS, ammonium sulfide-treated CIGS thin films, and samples with CdS. In bare CIGS, CGI ratio-dependent changes in PL are observed on both a low-energy (defect related transition) and a high-energy peak (band-to-band transition). After the surface treatment, the PL maximum increases by factors ranging from 4 to 11 depending on the CGI ratio, accompanied by a slower decay. Trends with similar improvement as in the PL study are observed in the performance of the solar cells. It is shown that the impact of the surface treatment is beneficial independently of the CGI ratio of the absorber layers. In all cases, the treatment is shown to improve the efficiency. This work received funding from the European Union's H2020 research and innovation program under grant agreement No. 715027. Buldu, DG (corresponding author), Hasselt Univ Partner Solliance, Inst Mat Res IMO, Agoralaan Gebouw H, B-3590 Diepenbeek, Belgium ; Imec Div IMOMEC Partner Solliance, Wetenschapspk 1, B-3590 Diepenbeek, Belgium ; EnergyVille, Thorpk,Poort Genk 8310 & 8320, B-3600 Genk, Belgium. Dilara.Gokcen.Buldu@imec.be

This work evaluates the potential of selective epitaxy to mitigate the recombination losses at the p-type contact regions of plated bifacial n-type PERT cells. Following the growth of a 500 nm, 2.5 10(19) cm(-3) boron doped epitaxial layer at the emitter contact regions defined by laser ablation of the passivating dielectrics, both an increase in V-oc (+6 mV) and FF (+ 1% absolute) are measured in the final cells compared to the reference with a homogeneous diffused emitter. These results come with an average efficiency gain of 0.3 and 0.5% absolute for front and rear side illumination, respectively. If the diffused, blanket emitter in the passivated regions is replaced by a thicker, lowly doped epitaxial profile (3 mu m, 5 10(18) cm(-3)) to further reduce recombination, an additional rise in implied V-oc after metallization of 10 mV is estimated. This increase would be the result of a reduction in J(0,pass, emitter) (down to 6 fA/cm(2)) and J(0,plated, emitter) (down to 1967 fA/cm(2)).

Copyright © 2018 John Wiley & Sons, Ltd. In this work, the ATOM (intrinsic a-Si:H/TiO x /low work function metal) structure is investigated to realize high-performance passivating electron-selective contacts for crystalline silicon solar cells. The absence of a highly doped Si region in this contact structure is meant to reduce the optoelectrical losses. We show that a low contact resistivity (ρ c ) can be obtained by the combined effect of a low work function metal, such as calcium (Φ 2.9 eV), and Fermi-level depinning in the metal-insulator-semiconductor contact structure (where in our case TiO x acts as the insulator on the intrinsic a-Si:H passivating layer). TiO x grown by ALD is effective to achieve not only a low ρ c but also good passivation properties. As an electron contact in silicon heterojunction solar cells, inserting interfacial TiO x at the i-a-Si:H/Ca interface significantly enhances the solar cell conversion efficiency. Consequently, the champion solar cell with the ATOM contact achieves a V OC of 711 mV, FF of 72.9%, J SC of 35.1 mA/cm 2 , and an efficiency of 18.2%. The achievement of a high V OC and reasonable FF without the need for a highly doped Si layer serves as a valuable proof of concept for future developments on passivating electron-selective contacts using this structure. ispartof: PROGRESS IN PHOTOVOLTAICS vol:26 issue:10 pages:835-845 status: published

© 2018 Elsevier B.V. In this paper a detailed study on the electrical characteristics of Ni/Cu/Ag plated p-type Passivated Emitter Rear Contact (PERC) silicon solar cells is reported. By comparing the cell performance of different cell groups, pseudo Fill Factor (pFF) degradation by laser-induced defects, is observed. High-power (hard) laser ablated cells exhibit a lower efficiency and faster degradation with thermal ageing. We also present structural and electrical characterization to further visualize and identify the responsible defects, which turn out to be laser-ablation-induced dislocations, penetrating the silicon emitter and base. Increasing the laser fluence gives rise to a higher dislocation density. These dislocations are further confirmed as active generation-recombination centers by Deep Level Transient Spectroscopy (DLTS) analysis. The laser ablation induced dislocations are unavoidable because even at insufficient laser fluence (0.48 J/cm2) to fully open the dielectric stack, the density is already at the level of 106/cm2. A substitutional nickel peak is also detected by DLTS, suggesting nickel diffusing into the silicon base during the sinter step. Whereas no copper levels are found in the p-type silicon base by DLTS even after thermal aging at 235 °C. ispartof: SOLAR ENERGY MATERIALS AND SOLAR CELLS vol:184 pages:57-66 status: published

Interface quality plays a key role in solar cell applications. Interface recombination at the front and rear surfaces, which determine this quality, have significant effects on open circuit voltage and fill factor values. In this work, several surface treatments were applied on Cu(In,Ga)Se2 (CIGS) surfaces to improve the interface quality. Besides, the passivation layer implementation was investigated to reduce interface recombination between the buffer and absorber layers.

The heterojunction interdigitated back-contact (HJ IBC) cell technology enables remarkably high cell efficiencies, but requirescomplex processing for the rear-side patterning of the interdigitated a-Si:H electron and hole hetero-contacts. Therefore, the HJ IBC process flow must be simplified into a sequence that is cost-effective and industrially-compatible. Towards this goal, a litho-free, all-dry process sequence is being developed. As part of this simplified process flow, a novel in situ dry clean process called “nano-envelope” clean is developed to replace the wet cleaning after dry etching of a-Si:H. Surface contaminationanalysis and passivation studies prove that the developed dry clean is as effective as the standard wet clean. Since the “nano-envelope” clean can bedone in the same PECVD tool, the sequence from dry etching to repassivation can be done fully in situ.

We present four-terminal perovskite-Si and perovskite-CIGS tandem solar modules that are fully scalable to commercial dimensions. Starting from small cells of 0.13 cm_2, we scale up the tandem devices by a factor of 30 to modules of 4 cm_2. By using a low-loss module design and optimized light coupling, we demonstrate perovskite-Si and perovskite-CIGS tandem solar modules which outperform the stand-alone devices on the large area, representing a key milestone for perovskite-based tandem photovoltaics. Moreover, the tandem solar module architecture is compatible with industrially scalable fabrication techniques, thus opening the route towards production of high-performance large-area perovskite-based tandem solar modules.

The replacement dynamics of Se by S is investigated in kesterite Cu 2 ZnSn(S,Se) 4 and Cu 2 ZnGe(S,Se) 4 . Two different post-sulphurization techniques yield the same results. In the initial stages of the replacement, the original selenium-rich phase coexists with a second mixed phase. This phase has an increased sulphur content of 30 %. In later stages of the reaction, the initial phase disappears in favor of the second phase. Thus, sulphur inclusions of less than 30% seem impossible while above 30% the sulphur amount is adjustable.

We present a novel approach to simplify the rearside a-Si:H patterning of silicon heterojunction interdigitated back-contact solar cells. In our current process, laser ablation and lift-off are used. Since lift-off is not industrially-viable, we propose to replace it with a selective deposition process which ensures a-Si: H is realised only on c-Si surface and not on the SiOx mask, at the end of the process, based on cycles of a-Si: H deposition and etching. While neither the deposition nor the etching is truly selective, this method relies on the difference of a-Si: H etch rates on c-Si and SiOx surfaces to achieve selectivity as the net end-result. The main challenge is addressing the trade-off between selectivity and c-Si surface passivation. The authors gratefully acknowledge the financial support of imec’s industrial affiliation program for Si-PV. This project has also received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement no. 727523 (NextBase).

© 2018 The Royal Society of Chemistry. Thin film perovskite photovoltaic devices combine high power conversion efficiencies with low weight, large area, high speed production capabilities and high versatility in form factor. With this paper, an additional feature is added to the device property portfolio: optical transparency. Results on translucent perovskite modules with selectively tuned levels of transparency are reported by applying the industrially established fabrication process of partial area ablation to high efficiency opaque devices. After process completion, the final devices consist of opaque areas that absorb the light, and transparent areas that permit neutral light transmission. We compare the effectiveness of using two active area removal techniques: mechanical scribing and laser ablation, and determine the factors that limit the maximum transparency and power conversion efficiency. Moreover, we show how the choice of the ablation method and design of the active area removal pattern affect and limit the maximum light utilization efficiency ratio that can be achieved with this fabrication process. The resulting 4 cm2 translucent modules cover a range of visible light transparency from 7 to 37% with a corresponding power conversion efficiency of 5 to 13%. ispartof: JOURNAL OF MATERIALS CHEMISTRY C vol:6 issue:12 pages:3034-3041 status: published

Encapsulants are known to have a large impact on the reliability of PV modules. Use of new materials such as low temperature solder can have an impact on how the encapsulant behaves in a module throughout its lifetime. A novel test methodology is used in this work to measure the adhesion strength between the encapsulant and its interfaces. The methodology is applied to both plated as screen printed metallization, low temperature SnBiAg solder and thermally evaporated Ag. The first steps in determining the underlying physical phenomena are studied experimentally for these interfaces as they can provide input for reliability models.

In this work, the addition of molar concentrations of Na+ and/or K+ in the form of fluorides during the processing of Cu2ZnSnSe4 absorber layers was investigated. The beneficial effect of alkali salts on the performance of CZTSe solar cells has been demonstrated through physical and electrical characterization. A maximum power conversion efficiency of 8.3% has been obtained through controlled addition of Na+ and K+ in the CZTSe absorber as opposed to 6.7% from uncontrolled addition of both. The open circuit voltage in both cases was very much the same but the devices with controlled addition showed lower p-type doping, a low density of charged defects and less band tailing compared to the rest.

This work proposes gallium oxide grown by plasma-enhanced atomic layer deposition, as a surface passivation material at the CdS buffer interface of Cu(In,Ga)Se-2 (CIGS) solar cells. In preliminary experiments, a metal-insulator-semiconductor (MIS) structure is used to compare aluminium oxide, gallium oxide, and hafnium oxide as passivation layers at the CIGS-CdS interface. The findings suggest that gallium oxide on CIGS may show a density of positive charges and qualitatively, the least interface trap density. Subsequent solar cell results with an estimated 0.5nm passivation layer show an substantial absolute improvement of 56mV in open-circuit voltage (V-OC), 1mAcm(-2) in short-circuit current density (J(SC)), and 2.6% in overall efficiency as compared to a reference (with the reference showing 8.5% under AM 1.5G). The work published in this paper was supported by the European Research Council (ERC) under the Union's Horizon 2020 research and innovation programme (grant agreement No 715027). The authors would also like to thank Dr. Marcel Simor (Solliance) for the CIGS layer fabrication and Prof. Johan Lauwaert (Universtiy of Ghent) for his guidance on DLTS measurements.

Using the thermal annealing of evaporated metallic precursors in successive H2Se and H2S atmospheres, it was possible to reproducibly manufacture kesterite absorber material for solar cell applications with a sulfur content varying from 30% to 100%. Respective band gaps for these sulfur inclusions were measured at approximately 1.45 eV and 2.0 eV. A recipe was devised for which results could be reproduced within an error margin of +/- 5% and the influence of the H2S pressure during the post sulfurization was negligible on all measurable and observable parameters. The evolution of the S/Se ratio in the sample was observed to be linearly dependent on the annealing time. It was also observed that at very early stages of the post-sulfurization, both the original Cu-2(Zn,Ge)Se-4 (CZGSe) and a primary Cu-2(Zn,Ge)(S,Se)(4) (CZGSSe) phase with a sulfur inclusion of similar to 30% coexist in the sample. The (112) x-ray diffraction (XRD) reflection of the CZGSe phase progressively disappears in favor for the first mixed CZGSSe phase. Using grazing incidence-XRD, the S/Se ratio was shown to be in homogeneous. Indeed, the XRD measurement of the top layers led to the calculation of higher sulfur inclusions than was the case when measuring the bulk material. Top-scanning electron microscopy (SEM) as well as cross-SEM measurements were taken in order to determine the impact of the sulfur inclusion on the crystal growth and the overall quality of the produced absorber layers. The obtained images revealed a reduction in crystal size and the appearance of numerous holes in the layer as the S/Se ratio is increased. This work was performed within the framework of the SWInG project funded by the European Union's Horizon 2020 research and innovation program, grant agreement No. 640868. M. Neuwirth gratefully acknowledges financial support by the German Federal Ministry of Education and Research (BMBF, FKZ: 03SF0530B) and the Karlsruhe School of Optics and Photonics (KSOP).

This paper compares the electrically active damage in dry-etched n-type float-zone silicon, using NF3/Ar or H2-plasma exposure and assessed by deep-level transient spectroscopy (DLTS) and recombination lifetime analysis. It is shown that the NF3/Ar-plasma damage consists of at least four different types of electron traps in the upper half of the band gap, which can be associated with vacancy- and vacancy-impurity-related complexes. In the case of H2-plasma damage, it is believed that the accumulation of point defects results in a gradual disordering of the near-surface layer. These defect levels also act as recombination centers, judged by the fact that they degrade the minority carrier lifetime. It is finally shown that lifetime measurements are more sensitive to the etching-induced damage than DLTS.This paper compares the electrically active damage in dry-etched n-type float-zone silicon, using NF3/Ar or H2-plasma exposure and assessed by deep-level transient spectroscopy (DLTS) and recombination lifetime analysis. It is shown that the NF3/Ar-plasma damage consists of at least four different types of electron traps in the upper half of the band gap, which can be associated with vacancy- and vacancy-impurity-related complexes. In the case of H2-plasma damage, it is believed that the accumulation of point defects results in a gradual disordering of the near-surface layer. These defect levels also act as recombination centers, judged by the fact that they degrade the minority carrier lifetime. It is finally shown that lifetime measurements are more sensitive to the etching-induced damage than DLTS.

One of the promising ways to increase the efficiency of silicon heterojunction (SHJ) cells is to replace the doped hydrogenated amorphous silicon (a-Si:H) contact layer by doped hydrogenated microcrystalline silicon (mu c-Si:H) which has better suited opto-electrical properties. In this work, we report on the development of a plasma-enhanced chemical vapor deposition process for mu c-Si:H. We demonstrate an n-type mu c-Si:H layer with high crystalline fraction and low parasitic absorption. The developed layer is implemented as the front electron contact of a SHJ cell. A significant improvement in J(sc) of 0.9 mA/cm(2) is achieved on device level while maintaining high V-OC values (> 725 mV), leading to an efficiency of 20.6% for the best cell. Cell efficiency is limited by a decreased FF which is attributed to the increased sensitivity of mu c-Si:H layers to ITO sputtering damage. The authors gratefully acknowledge the financial support of imec's industrial affiliation program for Si-PV. Part of this project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 657270.

A TiOx layer is well known as an electron-selective contact material because of its asymmetric band offsets with respect to c-Si. When applying TiOx layers as passivating electron-selective contacts, forming sub-stoichiometric TiOx is important to obtain a low contact resistivity because oxygen vacancies increase the conductivity of TiOx and provide n-type doping effects. In this work, oxygen vacancies at SiOx/TiOx interfaces are investigated by atomic depth profiling of XPS measurements. Three kinds of TiOx layers are studied grown by either e-beam evaporation, atomic layer deposition or sputtering on c-Si. In all three TiOx samples, a resulting stack of c-Si/SiOx/TiOx could be noticed XPS measurements that show SiOx peaks near the c-Si/TiOx interface. Moreover, clear TiO2 peaks, which can be measured at the surface of all three TiOx layer types, gradually change to Ti or TiSi2 peaks near the SiOx/TiOx interface. This indicates that many oxygen vacancies seem to exist at the SiOx/TiOx interface. This TiOx reduction may contribute to the formation of a dipole and increased downward band bending resulting in a lower contact resistivity in the electron-selective contacts. As a result, hetero-junction solar cells with i-a-Si:H/TiOx/Ca/Al contacts exhibit a significant series resistance reduction of about 40 % compared to solar cells with i-a-Si:H/Ca/Al contacts.

Dry plasma etching, commonly used by the Photonics community as the etching technique for the fabrication of photonic nanostructures, could be a source of device performance limitations when used in the frame of silicon photovoltaics. So far, the lack of silicon solar cells with state-of-the-art efficiencies utilizing nanophotonic concepts shows how challenging their integration is, owing to the trade-off between optical and electrical properties. In this study we show that dry plasma etching results in the degradation of the silicon material quality due to (i) a high density of dangling bonds and (ii) the presence of sub-surface defects, resulting in high surface recombination velocities and low minority carrier lifetimes. On the contrary, wet chemical anisotropic etching used as an alternative, leads to the formation of inverted nanopyramids that result in low surface recombination velocity and low density of dangling bonds. The proposed inverted nanopyramids could enable high efficiency photonic assisted solar cells by offering the potential to achieve higher short-circuit current without degrading the open circuit voltage. (© 2016 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

Numerous models have been developed to predict the power output of photovoltaic (PV) systems as a function of insolation and ambient conditions. However, the effect of wind on module temperature, and hence performance, is only poorly incorporated into these models, and spatially distributed and (fast-varying) transient wind effects have not yet been studied in detail. In this paper, spatial distribution of temperature over a 156 × 156 mm PV mini-module is studied together with fine-time-scale temporal evolution. Tests were performed on a 2 × 3 mini-module mounted in a wind tunnel. Results show that the temperature differences can amount to 21 °C and more, depending on the wind speed and the location on the module. Apart from cooling caused by heat convection, a temperature increase generated by wind friction also occurs at the module’s surface although it remains very low compared to the cooling caused by convection.

We discuss the effect of out-of-plane excess carrier density variations on contact recombination currents extracted from quasi steady state photoconductance (QSSPC) measurements on a dedicated test structure. The test structure features lattices of point contacts. The contacts are thick and non-transparent. Therefore, asymmetric test structures are generally used to ensure a homogeneous in-plane generation rate. As a result, the QSSPC measurements are relatively prone to out-of-plane excess carrier density variations. Their effect on the extracted contact recombination characteristic is discussed theoretically and the theory is confirmed by experiment. The resulting framework contributes to the set of design rules and best practices for contact recombination current characterization using QSSPC measurements on point contact lattice based test structures.

Cu2ZnSi(S,Se)4 and Cu2Si(S,Se)3 are potential materials to obtain cost effective high band gap absorbers for tandem thin film solar cell devices. A method to synthesize Cu2SiS3, Cu2SiSe3and Cu2ZnSiSe4thin film absorbers is proposed. This method is based on a multistep process, using sequential deposition and annealing processes. X-ray diffraction analysis performed on the final thin films have confirmed the presence of the Cu2Si(S,Se)3 and Cu2ZnSiSe4phases. Scanning electron microscopy images revealed the formation of polycrystalline layers with grains size up to 1 µm. The band gap of the ternary Cu2SiSe3 and Cu2SiS3, and quaternary Cu2ZnSiSe4 based thin films as determined from optical and photoluminescence measurements are found to be close to their theoretical values. (© 2015 WILEY-VCH Verlag GmbH &Co. KGaA, Weinheim)

We report on the electrical, optical and physical properties of Cu2ZnSnSe4 solar cells using an absorber layer fabricated by selenization of sputtered Cu, Zn and Cu10Sn90 multilayers. A maximum active-area conversion efficiency of 10.4% under AM1.5G was measured with a maximum short circuit current density of 39.7 mA/cm(2), an open circuit voltage of 394 mV and a fill factor of 66.4%. We perform electrical and optical characterization using photoluminescence spectroscopy, external quantum efficiency, current-voltage and admittance versus temperature measurements in order to derive information about possible causes for the low open circuit voltage values observed. The main defects derived from these measurements are strong potential fluctuations in the absorber layer as well as a potential barrier of the order of 133 meV at the back side contact. (C) 2014 Elsevier B.V. All rights reserved.

One of the promising low cost and non-vacuum approaches for the fabrication of semiconductor CuInSe 2 and Cu(In,Ga)(S,Se) 2 thin film absorbers is the printing of precursor materials followed by a sintering/selenization process. The selenization process parameters such as temperature, duration, and selenium vapor pressure strongly influence the morphology and electronic properties of the absorber film. In this study, the effect of pre-annealing in an inert atmosphere and selenization on printed mechanically synthesized CuInSe 0.5 alloy nanopowder precursor films was investigated. 1–2 μm thick CuInSe 0.5 alloy nanopowder layers were deposited on a Mo-sputtered glass substrate by means of doctor blade coating of a nanopowder based precursor suspension. Pre-annealing was performed on a hot plate inside a nitrogen gas filled glove box. Selenization was performed in a home-made rapid thermal processing (RTP) furnace with two RTP heating zones for independent temperature control of the selenium source and the coated substrate. The temperature of the selenium source was fixed at 390–410 °C during the selenization to provide a constant supply of selenium vapor. A two-step process, i.e., a pre-annealing in nitrogen atmosphere at 400 °C for 30 min followed by selenization at 530 °C for 15 min was found to result in better densification and grain growth of the CuInSe 2 phase, compared to a single step selenization at 530 °C for 15 min. The solar cell fabricated by the two-step process had an efficiency of 5.4% and a fill factor of 52%, while the device fabricated by the single step selenization had an efficiency of 1.1% and a fill factor of 31%.

Cu2nSnSe4 (CZTSe) thin film solar cells are promising emergent photovoltaic technologies based on low-bandgap absorber layer with high absorption coefficient. To reduce optical losses in such devices and thus improve their efficiency, numerical simulations of CZTSe solar cells optical characteristics can be performed based on individual optical properties of each layer present in the cell structure. In this contribution, we have first determined the optical coefficients of individual thin films (i.e., (n, k) of the absorber, buffer, and window layers) to build a realistic model simulating the optical behavior of the whole cell stack we propose. Optical characterization was performed using two approaches, one based on ellipsometry measurements for characterizing thin flat cadmium sulfide (CdS) and zinc oxide (ZnO) layers and the other relying on reflectance and transmission (R/T) analysis for the rough CZTSe absorber. Then, we performed numerical simulations using as input experimental optical parameters predicting optimal CZTSe cell structure minimizing optical losses. The impact of each layer's thickness on the cell's short-circuit current has been studied. A set of optimal thicknesses of each of the active layers was proposed. Finally, the proposed optical optimization was experimented practically leading to CZTSe cells with 9.7% and 10.4% efficiencies. cop. 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Argon (Ar) and oxygen (O2) plasmas are performed on silicone adhesives to eliminate the negative influence of silicone on amorphous silicon (a-Si:H) surface passivation of wafers bonded to glass. Both the Ar and O2 plasmas lead to oxidation of the silicone surface, consisting in an increase of oxygen/carbon ratio, of degree of crosslinking, and of material density. The oxidized silicone is more resilient than pristine and does not interact with the a-Si:H passivation process, allowing for state-of-the-art surface passivation of wafers bonded to glass. Similarities between the modifications induced by the Ar and O2 plasmas on the silicone indicate the secondary role of the O2 radicals in the oxidation process. Moreover, amorphous/crystalline heterojunction interdigitated back contact solar cells (a-Si:H/c-Si HJ i-BC) are fabricated on freestanding and bonded wafers treated with Ar plasma. The devices show comparable open-circuit voltages of up to 675 mV, confirming at device level the efficacy of the treatment.

Two important aspects for the success of the porous silicon-based layer transfer method in producing kerfless thin ( 15 cm −3 which corresponds to a minimum minority carrier diffusion length of ~670 µm (> 16 times the silicon thickness). With such high quality epitaxial foils combined with high detachment yield, very high efficiency solar devices on thin silicon substrates would be a reality in the near future.

In the future solar devices will be manufactured onto thin mono-crystalline silicon wafers (foils) potentially bonded to substrate carriers. In this study, the influence of the substrate carrier potential (grounded or floating) on the amorphous silicon a-Si:H surface passivation of the bonded foil is discussed for the cases of conductive and insulating substrate carriers. A conductive carrier leads to an increase in deposition rate and ion bombardment energy, which is detrimental for sample lifetime. An insulating carrier, e.g., a glass substrate, inverts the trend and improves the a-Si:H surface passivation.

We have investigated fine grained polycrystalline silicon thin films grown by direct chemical vapor deposition on oxidized silicon substrates. More specifically, we analyze the influence of the doping type on the properties of this model polycrystalline silicon material. This includes an investigation of defect passivation and benchmarking of minority carrier properties. In our investigation, we use a variety of characterization techniques to probe the properties of the investigated polycrystalline silicon thin films, including Fourier Transform Photoelectron Spectroscopy, Electron Spin Resonance, Conductivity Activation, and Suns-Voc measurements. Amphoteric silicon dangling bond defects are identified as the most prominent defect type present in these layers. They are the primary recombination center in the relatively lowly doped polysilicon thin films at the heart of the current investigation. In contrast with the case of solar cells based on Czochralski silicon or multicrystalline silicon wafers, we conclude that no benefit is found to be associated with the use of n-type dopants over p-type dopants in the active absorber of the investigated polycrystalline silicon thin-film solar cells.

In this paper, we examine photoluminescence spectra (PL) of Cu2ZnSnSe4/CdS/ZnO solar cells, based on an absorber layer fabricated by selenization of sputtered Cu, Zn, Sn multilayers, via temperaturedependent and illumination power-dependent measurements. We observe anomalous emission behavior: the PL peak initially decreases with increasing temperature (red shift) in the temperature range 10– 60 K, followed by a blue shift at higher temperature in the range 60–180 K. A recombination model is proposed that is able to explain both temperature dependent PL as well as power-dependent PL. The important aspect of the proposed model is taking into account the presence of strong potential

In this work, we present the incorporation of a laser doped selective emitter into the i-PERC platform at Imec using large area magnetically confined boron-doped Czochralski grown silicon wafers. Cells were fabricated with self-aligned plated n-type contacts with a comparison between the use of a homogenous emitter with contact openings formed by picosecond laser ablation and a selective emitter formed by laser doping with a mode-locked UV laser using various processing speeds. Without modification to other processes in the i-PERC platform, improvements in efficiency of approximately 0.4% absolute were obtained with the inclusion of the selective emitter structure through improvements in open circuit voltage, fill factor and reduced series resistance. This resulted in peak efficiencies of 20.5% using a processing speed for laser doping of 5 m/s.

Modification of the absorber surface properties by Cd2+ treatment (Cd2+ partial electrolyte) results in the following: formation of Cd(OH)2 on the absorber surface, deposition of thinner chemical bath-deposited CdS buffer layer, and a smaller space charge region. The impact on electrical performances is as follows: decrease of the series resistance (RS), increase of the fill factor, increase of the efficiency (η), and reduction of the crossover between the dark and light current density-voltage curves. The present contribution aims at determining the impact of modifying the properties of the absorber/buffer layer interface on the electrical performance of Cu2ZnSnSe4 (CZTSe) thin-film solar cells, by using a Cd2+ partial electrolyte (Cd PE) treatment of the absorber before the buffer layer deposition. In this work, CZTSe/CdS solar cells with and without Cd PE treatment were compared with their respective Cu(In,Ga)Se2 (CIGSe)/CdS references. The Cd PE treatment was performed in a chemical bath for 7 min at 70 °C using a basic solution of cadmium acetate. X-ray photoemission spectroscopy measurements have revealed the presence of Cd at the absorber surface after the treatment. The solar cells were characterized using current density-voltage (J-V), external quantum efficiency, and drive-level capacitance profiling measurements. For the CZTSe-based devices, the fill factor increased from 57.7% to 64.0% when using the Cd PE treatment, leading to the improvement of the efficiency (η) from 8.3% to 9.0% for the best solar cells. Similar observations were made on the CIGSe solar cell reference. This effect comes from a considerable reduction of the series resistance (RS) of the dark and light J-V, as determined using the one-diode model. The crossover effect between dark and light J-V curves is also significantly reduced by Cd PE treatment.

The influence of the cleaning process on the amorphous silicon passivation of homojunction emitters is investigated. A significant variation in the passivation quality following different cleaning sequences is not observed, even though differences in cleaning performance are evident. These results point out the effectiveness of our cleaning treatment and provide a hydrogen termination for intrinsic amorphous silicon passivation. A post-deposition treatment improves the passivation level yielding emitter saturation currents determined by Auger recombination in the order of 70 fA/cm2 and below.