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A back-contact perovskite solar cell (BC-PSC) has been simulated. The J–V curves were calculated with different degrees of the interfacial recombination, and the characteristics of basic physical phenomena inside the device, including carrier concentration distribution, ion concentration distribution, electric potential change, and carrier recombination rate, have also been investigated. It was found that the effect of the perovskite layer's upper surface (US) interfacial recombination on the hysteresis phenomenon is greater than that of the perovskite layer's lower surface (LS) interfacial recombination. In addition, it has been found that the inverted hysteresis phenomenon occurs in the BC-PSC with the LS interfacial recombination. Moreover, the hysteresis loops corresponding to the US interfacial recombination of the perovskite layer were close to the short-circuit current side, and the hysteresis loops corresponding to the LS interfacial recombination of the perovskite layer were close to the open-circuit voltage side. These results indicate that both of the US and LS interface recombinations in the BC-PSC play a crucial role in the hysteresis phenomenon. [ABSTRACT FROM AUTHOR]

In this viewpoint, recent hot topics in the photovoltaic community, interdigitated back contact (IBC) cells, are systematically reviewed from the view of device configuration. Two categories of IBC designs on the most popular perovskite solar cells (PSCs) were discussed, and a planar back-contact perovskite module was first proposed. The device configuration, fabrication methods, working mechanism, optimization strategies, and future development directions of this novel PSC module were put forward to show its superiorities in the module performance, processing difficulty, and extensible functionality among present perovskite modules, presenting promising potential to improve the competitiveness of perovskite technology in the photovoltaic market.

Back-contact perovskite solar cells are of great interest because they could achieve higher performance than conventional designs while also eliminating the need for transparent conductors. Current research in this field has focused on making electrode structures with reduced widths to collect charges more efficiently, but current lift-off-based fabrication techniques have struggled to achieve electrode widths smaller than 1000 nm and are difficult to implement on large areas. We demonstrate nanoimprint lithography in an etch-down procedure as a simple and easily scalable method to produce honeycomb-shaped, quasi-interdigitated electrode structures with widths as small as 230 nm. We then use electrodeposition to selectively deposit conformal coatings of a range of different hole-selective layers and explore how the efficiency of back-contact perovskite solar cells changes as the feature sizes are pushed into the nanoscale. We find that the efficiency of the resulting devices remains almost unchanged as the electrode width is varied from 230 to 2000 nm, which differs from reported device simulations. Our results suggest that reducing recombination and improving the quality of the charge transport layers, rather than reducing the minimum feature size, are likely to be the best pathway to maximizing the performance of back-contact perovskite solar cells. [ABSTRACT FROM AUTHOR]

The efficiency of back‐contact perovskite solar cells has steadily increased over the past few years and now exceeds 11%, with interest in these devices shifting from proof‐of‐concept to viable technology. In order to make further improvements in the efficiency of these devices it is necessary to understand the cause of the low fill factor, low open‐circuit voltage (VOC), and severe hysteresis. Here a time‐dependent Suns‐Voc and Suns‐photoluminescence (PL) analysis are performed to monitor the transient ideality factor spatially. Two sets of quasi‐interdigitated back‐contact perovskite solar cells are studied; cells with and without a mesoporous TiO2 layer. Maps of the PL intensity and ideality factor resemble the periodic structure of the back‐contact electrodes and the transient behavior exhibit distinct features such as a temporary variation in the periodicity of the modulation, spatial phase shifting, and phase offsets. It is shown that the presence of the mesoporous layer greatly reduces recombination, increasing the VOC by 0.12 V. Coupled 2D time‐dependent drift‐diffusion simulations allow the experimental results to be modeled, and replicate the key features observed experimentally. They reveal that non‐uniform ion distribution along the transport layer interfaces can drastically alter the PL intensity and ideality factor throughout the device. [ABSTRACT FROM AUTHOR]

Perovskites have already shown potential as active layers in photovoltaic applications. Furthermore, a low-cost and simple solution processing technology allows perovskites to be used in flexible and printed electronics. Perovskite solar cells (PSC) with a back-contact (BC) structure, in which the electrode system is based on a quasi-interdigitated back-contact (QIBC) design, promise to increase the power conversion efficiency (PCE) of devices beyond those that can be obtained using PSCs with a traditional sandwich structure. While the spin-coating technique is used to deposit the perovskite layer of lab-scale BC PSCs, the application of large-area printing techniques to deposit the perovskite layer of such devices is yet to be explored. Therefore, this work demonstrates an application of the slot-die coating technique to print the perovskite active layer of BC PSCs with QIBC electrodes on flexible polymer substrates. The morphology of the obtained perovskite films on QIBC electrodes are investigated and the primary photoelectric parameters of the resulting BC PSCs are measured. The charge carrier recombination processes in the fabricated BC PSCs are investigated and the dominant mechanism for carrier loss in the devices is determined. The findings of the work give an insight into the properties of the slot-die-coated perovskite active layer of BC PSCs and points to exciting new research opportunities in this direction. [ABSTRACT FROM AUTHOR]

Perovskites are a promising class of semiconductor materials, which are being studied intensively for their applications in emerging new flexible optoelectronic devices. In this paper, device manufacturing and characterization of quasi-interdigitated back-contact perovskite solar cells fabricated on flexible substrates are studied. The photovoltaic parameters of the prepared flexible quasi-interdigitated back-contact perovskite solar cells (FQIBC PSCs) are obtained for the front- and rear-side illumination options. The dependences of the device's open-circuit potential and short-circuit current on the illumination intensity are investigated to determine the main recombination pathways in the devices. Spectral response analysis of the devices demonstrates that the optical transmission losses can be minimized when FQIBC PSCs are illuminated from the front-side. Optoelectronic simulations are used to rationalize the experimental results. It is determined that the obtained FQIBC PSCs have high surface recombination losses, which hinder the device performance. The findings demonstrate a process for the fabrication of flexible back-contact PSCs and provide some directions for device performance improvements. [ABSTRACT FROM AUTHOR]

• Flexible SUS-mesh with optimally protected Ti metal was proved to be an efficient photoanode. • The interfacial contact between the nanoporous TiO 2 and flexible photoanode was found to influence the device performance. • TiO 2 with relatively larger particle size provided facile charge transport. Transparent-conductive-oxide-free (T-C-O-free) back-contact (B-C) dye-sensitized solar cell (DSC) utilizing flexible Stainless Steel (SS) mesh (SS-mesh) supported with mesoporous TiO 2 as a photoanode employing cobalt electrolyte is being presented. A thin layer of Ti metal over the SS-mesh was ascertained to be essential to retard the back electron reaction, which was confirmed by the dark current measurements. The interfacial contact between the SS-mesh and nanoporous (NP) TiO 2 of the photoanode of T-C-O-free B-C-DSC was driven to influence the photovoltaic performance greatly. It was confirmed by electrochemical impedance analysis that NP TiO 2 of 30 nm exhibited less charge transfer impedance observed at TiO 2 -dye-electrolyte interface as compared to TiO 2 of having particle size of 15–20 nm. T-C-O-free B-C-DSC employing dye mixer combination of indoline dyes D-131 and D-205 (1:1) with relatively larger NP of TiO 2 (30 nm) as compared to TiO 2 of 15–20 nm exhibited enhanced photoconversion efficiency (PCE) of 4.02%. To increase the PCE even further, T-C-O-free B-C-DSC with cobalt based electrolyte sensitized with porphyrin (YD2-o-C8)-dye bearing a larger optical window was investigated. An optimized 10 µm thickness of the TiO 2 layer was found to be optimum leading to an enhanced PCE of 5.26%. [ABSTRACT FROM AUTHOR]

• Computer simulation method is used to study back-contact perovskite solar (BC-PSCs). • Geometric parameters of quasi-interdigitated electrodes (QIDEs) are optimized. • Optimum electronic properties for the perovskite layer are obtained. • BC-PSC with QIDEs have low optical transmission losses. A numerical simulation method is used to investigate intricacies of a complex relation between the back-contact electrode (BCE) geometric parameters, the perovskite photo-absorber layer electronic properties, and device performance in back-contact perovskite solar cells (BC-PSCs) with quasi-interdigitated electrodes (QIDEs). To unlock the full potential of BC-PSC with QIDEs, the device performance was investigated by systematically varying the geometric parameters of BCE and the perovskite photo-absorber layer electronic parameters in order to determine the conditions for a best device performance. BC-PSC with QIDEs have a potential to produce power conversion efficiencies (PCEs) higher than PSCs with the conventional sandwich architecture if optimized parameters for electrode geometry and perovskite electronic properties are used. The findings of the present work give an insight into the work principle of these devices and provide a theoretical guidance for design and fabrication of high-performance BC-PSC with QIDEs. [ABSTRACT FROM AUTHOR]

• J ph of 24.03 mA/cm2 is received under 300 nm-thick and 1.55 eV band gap. • Excellent optical performance is mainly attributed to the light trapping effect. • High J ph maintains under varied perovskite thickness, band gap and incident angles. • The internal quantum efficiency (IQE) is study by a brief electrical simulation. Interdigitated back-contact (IBC) structure has been successful explored for optimal light-harvesting in the silicon solar cells (SCs), but less used in perovskite solar cells (PSCs). To unlock the full potential of IBC PSCs, we investigate numerically the photo-electrical performance of this type of IBC PSCs, designing the light-trapping structures and screening the functional materials. Taking the experimental quasi-interdigitated back-contact (QIBC) structure as the original model, the optical absorption of PSCs can be boosted by befitting anti-reflective coating thickness and rear substrate materials. And then the QIBC PSC yields the maximal photocurrent density of 24.03 mA/cm2, 4.19 mA/cm2 higher than that of the conventional sandwich PSC. The light-trapping effect of QIBC architecture is discussed by addressing the absorption spectra and the cross-sectional electric field distributions of perovskite layer. Besides, better optical properties can be well maintained in a large range of film thickness and band gap of perovskite, as well as incident angles, compared with that of sandwich PSC. More importantly, an approximate electrical simulation is implemented, revealing the relationship between the internal quantum efficiency, the carrier diffusion length of perovskite and the electrode finger distance. Therefore, the simulation results are expected to provide the theoretical guidance for developing high efficiency IBC PSCs. [ABSTRACT FROM AUTHOR]

• The effective back-contact barrier of CZTSe: nanoscale Ge is improved and characterized. • The mechanism of the back-contact improvement is demonstrated with device models. • The model of MoSe 2 interface defect at back-contact agrees with the empirical data. • The efficiency is improved up to 8.3% by including nanolayer Ge at back contact. Using temperature-dependent measurements and device modeling, we systematically study the effective back-contact barrier of CZTSe devices to improve the property of the back-contact interface. By comparing with CZTSe devices with various nanoscale Ge configurations, CZTSe nanoscale Ge bi-layers devices show the improved power conversion efficiency by 1.1%. DC magnetron sputtering is used to fabricate CZTSe: nanolayer Ge devices. Critical device parameters are characterized to understand the impact of nanoscale Ge films on the back-contact device characteristics. Based on empirical results, modeling is performed for the influence of MoSe 2 defects on the effective back-contact barrier. Analysis of experimental results of Ge bi-layers devices with the improved back-contact barrier makes a good agreement with modeling and Sentaurus TCAD simulation at the 95% confidence-level. The conversion efficiency of CZTSe: nanoscale Ge bi-layers devices is improved up to 8.3%. [ABSTRACT FROM AUTHOR]

Summary: Perovskite solar cells are one of the most promising photovoltaic technology, presenting the fastest power conversion efficiency (PCE) growth from 3.8 % to 24.2 % in just 10 years. However, there are still challenges hindering its commercialization such as the expensive back‐contact made of gold. Carbon‐based materials, mainly carbon pastes made of carbon black and graphite, have already proven to be good candidates as back‐contacts because of their features such as low cost, high conductivity, and high stability. In this work, the replacement of gold back‐contact by a carbon paper with a microporous layer coated with a PEDOT:PSS dispersion is reported. To the best of the author's knowledge, this material has never been reported for perovskite solar cells. A PCE of 9.22 % was obtained, representing 62 % of the PCE obtained for the same cell but with a gold back‐contact. [ABSTRACT FROM AUTHOR]

Silicon solar cells incorporating double-sided pyramidal texture are capable of superior light trapping over cells with front-side only texture. However, increased surface area, roughness and exposed <111> crystal planes of textured surfaces not only causes increased recombination, but also makes cells susceptible to shunting through pinholes in the dielectric at the sharp peaks and valleys of the textured pyramids. A polyimide film as an insulating interlayer film is investigated to circumvent the tradeoff between improved light trapping, increased recombination and increased shunt paths. When applied at the rear of the interdigitated back contact silicon solar cell structure, the polyimide film provides an excellent electrical insulation (> 1000 MΩ of insulation resistance) and increases photocurrent (~ 1.1 mA/cm 2 ) owing to an increased rear internal reflectance. The polyimide is also compatible with metal annealing of passivating dielectrics such as silicon nitride. Optical simulation and experimental results are combined in a 3D semiconductor simulation (Quokka) to quantify the possible gain of implementing the double-sided texture in high efficiency silicon solar cells. [ABSTRACT FROM AUTHOR]

Back-contact electrodes have been broadly applied to silicon photovoltaics to enhance their performance and avoid parasitic absorption from window materials and charge collection grids [1,2]. Here we introduce an innovative back-contact design for perovskite solar cells (PSCs) derived from our recently described quasi-interdigitated back-contact architecture [3]. The back contact consists of a top electrode, which has a honeycomb-like grid geometry, that is separated from the underlying planar bottom electrode by a similarly shaped insulating Al 2 O 3 layer. This new design has higher structural robustness, as well as better defect tolerance, resulting in the highest short-circuit current (~ 16.4 mA/cm 2 ) and stabilized power output (~ 4%) for a back-contact PSC to date. The improved performance was attributed to an increased charge collecting efficiency, with photocurrent mapping revealing what electrode dimensions are required for optimum efficiency. [ABSTRACT FROM AUTHOR]

In the manufacturing process of a common solar module, crystalline silicon solar cells are interconnected by soldering. Copper-based interconnectors, coated with a solder alloy are soldered on both sides of the solar cells on the contact metallization. Subsequently, the solar cell strings are embedded in between two sheets of encapsulant, commonly ethylene-vinyl acetat (EVA), which itself attaches to a front glass and a back sheet during the lamination process. Thermomechanical stress, due to the mismatch of the coefficients of thermal expansion (CTE) of copper and silicon, causes bowing of a back-contact solar cell after the soldering process. Additionally, thermomechanical stress can result in the failure of solder joints. By adapting the mechanical properties of an interconnector, thermomechanical stress can be reduced. Shaping a straight wire with a round cross section to a wave-like form reduces its effective tensile mechanical properties and leads to changes of its effective electrical conductivity. This study investigates the mechanical and electrical properties of wave-shaped wires with different amplitudes, periods and diameters. In addition, microscopic imaging reveals the geometry and potential defects due to the shaping process. The influence of the shaping process on the yield limit of commercially available copper-based wires is determined. For this reason, an algorithm is designed that allows the automatic and precise determination of the yield limit of these interconnectors. In this study, a maximum yield limit reduction of 88.5% compared to a straight wire is found. Furthermore, the influence of the shaping process on the electrical resistance is analyzed. For this purpose, the influence of wire damaging due to the shaping process, as well as the wires longitudinal length change is determined. An increase of the electrical resistance between 3.5% and 82.7% is measured. To choose an optimal interconnection concept for solar cells, the mechanical, as well as the electrical properties of the interconnectors have to be considered. This study correlates the advantageous longitudinal softness of wave-shaped wires, which potentially leads to a significant decrease of the thermomechanical stress in solar cells and of the bowing of back-contact solar cells, with the disadvantageous increase of the electrical resistance caused by the shaping process. The findings enable an optimization of a wire-based interconnection concept for back-contact solar cells. [ABSTRACT FROM AUTHOR]

We report on the fabrication and characterization of Cu(In,Ga)Se 2 (CIGS)-based thin film bifacial solar cells using Al-doped ZnO (AZO) as cost-effective and non-toxic transparent back contact. We show that, by depositing both CIGS and AZO by Low Temperature Pulsed Electron Deposition at a maximum temperature of 250 °C, a good ohmic contact is formed between the two layers and good quality solar cells can be fabricated as a result. Photovoltaic efficiencies as high as 9.3% (front illumination), 5.1% (backside illumination) and 11.6% (bifacial illumination) have been obtained so far. These values are remarkably higher than those previously reported in the literature. We demonstrate that this improvement is ascribed to the low-temperature deposition process that avoids the formation of Ga 2 O 3 at the CIGS/AZO interface and favours the formation of a low-resistivity contact in agreement with device simulations. [ABSTRACT FROM AUTHOR]

Standard characterization techniques such as LBIC are difficult to apply to IBC solar cells with a front floating emitter (FFE). This is because the cells need to be under bias illumination, and this is often impossible in commercial LBIC measurement tools. To the best of our knowledge, LBIC measurements on FFE IBC cells have not been published so far. In this work we present a experimental method to spatially characterize the FFE of IBC cells and gain insights on electrical shading losses, without using LBIC. This method makes use of the commercially available CoreScan device, mapping the FFE voltage relative to the shorted back-contacts over the cell area. Using this technique we were able to resolve busbar, pads and finger features of both polarities with a scan of the front side. The scan shows that BSF features have higher voltage than emitter features, thus giving a direct evidence of the FFE pumping effect. If coupled to circuit simulation, FFE voltage maps can be the base for estimating electrical shading losses in IBC cells. The FFE voltage maps also give information on the homogeneity of the pumping effect across the wafer, e.g. affected by diffusion non-uniformity, and at least qualitatively its effect on the cell performance. [ABSTRACT FROM AUTHOR]

ECN set up a cross testing project in which suppliers of electrically conductive adhesives (ECA) and conductive back-sheet (CBS) foils participated. In the component part of the project, combinations of adhesive and foil were characterised for peel strength and contact resistance. The separate components were tested on dot geometry (ECA) and surface structure (CBS). In the module manufacture and testing part, 12 combinations of ECA and CBS were used in 4-cell MWT modules. The modules were tested up to 2000 hours in damp heat and 400 thermal cycles (both tests, 2 times the requirement of IEC61215). Most combinations passed the 5% power loss criterion. One of the conductive adhesives performed well on three different types of back-sheet which is supportive of a robust technology. Other results show that it is important to thoroughly test interesting combinations of ECA and CBS at module level before adding them to the recommended bill of materials. [ABSTRACT FROM AUTHOR]

Abstract: We investigate the formation of deep Phosphorus diffusion profiles with low surface concentrations in one single diffusion step. Such processes are suited for front surface field formation for n-type back-contact back-junction (BC- BJ) silicon solar cells or p-type silicon solar cells with alternative metallization techniques. The deposition temperature allows accurate control of the sheet resistance whereas the temperature of the in-situ oxidation strongly influences the profile-depth and surface concentration. The newly developed process leads to low dark saturation current densities well below 30 fA/cm2 on alkaline-textured surfaces and low short circuit current loss at the front side. Due to their depth and adjustable surface concentration, the obtained profiles are promising for front-surface- fields (FSF) and novel n-type emitters. A first implementation in BC-BJ solar cells with aluminum-alloyed emitter shows a good blue response of the solar cells and an improved efficiency compared to the reference process by 0.6%abs. [Copyright &y& Elsevier]

Abstract: The collaboration between the Solar Energy Research Institute of Singapore (SERIS), Trina Solar and ANU is progressing well, and ANU has already developed all-back-contacted (ABC) silicon wafer cells with best one-sun efficiencies of 21.2% and 22.1% on FZ material, when measured with the aperture areas of 16cm2 (includes busbars) and 13cm2 (excludes busbars) respectively. This paper presents the continuing development of ABC cells targeting the efficiency of 23.5% on 16-cm2 cell area. Further developments such as optimising front surface field (FSF), rear diffusion, anti-reflection coating (ARC), and incorporation of lithographically aligned metal contacts were undertaken on the ABC cells. Phosphorus diffusion of the FSF was made lighter from the sheet resistance of 190Ω/□ to 240Ω/□, resulting in the reduction of the saturation current density (Joe) of the FSF by 22 fA/cm2. The optimised thickness of anti-reflection coating (ARC) PECVD SiNx further reduces the average reflectance across the wavelength range of 300 to 1200nm by about 4%. Incorporation of aligned metal contacts and heavier rear phosphorus diffusion has contributed to the reduction in the total series resistance by 0.08Ωcm2. The above optimised improvements have increased the efficiency of the champion ABC cell by 0.5% absolute. In addition, we present further refinements in areas of texturing; FSF passivation; electrical shading loss in terms of cell pitch, bus- bar and base doping; and metallisation to aim for the 16-cm2 ABC cells with the conversion efficiency > 22% in the near term. [Copyright &y& Elsevier]

Abstract: Silicon remains the material of choice for photovoltaics because of its abundance, non-toxicity, high and stable cell efficiencies, the maturity of production infrastructure and the deep and widespread level of skill available in relation to silicon devices. Rapidly decreasing module prices mean that area-related balance of systems costs are an increasing proportion of photovoltaic systems price. This places a premium on efficient cells. In recent years there have been large improvements in mass production of high quality wafers, the ability to handle thin wafers, maintenance of high minority carrier lifetimes, surface passivation, minimisation of optical losses, device characterisation and in other areas. Many of these improvements are viable in mass production. The upper limit of silicon solar cell efficiency is 29%, which is substantially higher than the best laboratory (25%) [1] and large-area commercial (24%) [2,3] cells. Cell efficiencies above 25% appear to be feasible in both a laboratory and commercial environment. Such a cell will have minimal bulk recombination due to a combination of a thin substrate with a very high minority carrier lifetime; superb surface passivation; small-area electrical contacts consistent with low contact recombination, free carrier absorption and contact resistance; excellent optical control through the use of texturing, antireflection coatings and rear surface reflectors; low edge recombination assisted by the use of thinner wafers, larger cells and edge passivation; and sufficient metal coverage to minimise resistive losses. This paper will survey current work in high- performance silicon solar cell design and fabrication, and discuss approaches to efficiency improvements. [Copyright &y& Elsevier]

Abstract: All-screen-printed back-contact back-junction silicon solar cells with aluminum-alloyed emitter on n-type base material were fabricated and analyzed at Fraunhofer ISE PV-TEC. Three different process sequences are compared to each other. One process flow with shallow phosphorus profiles realizes cells with efficiencies of 19.7%. Using a long thermal oxidation, cells with deep driven-in phosphorus profiles (front and back surface field) were processed where solar cell efficiencies of 20.0% are realized. Both cell efficiencies are independently measured at Fraunhofer ISE CalLab on a designated area of 16.65cm2. The specific contact resistivity of screen-printed and fired silver paste to silicon surfaces with different phosphorus profiles was determined in dependence of several firing conditions. The main developed features of the presented cell structure comprise the firing-stable front and rear passivation layers, the spiking-free passivation layer against aluminum and the deep driven-in phosphorus profile that can be contacted by silver screen-printing paste in a firing step. [Copyright &y& Elsevier]

Abstract: The performance of n-type Si back-contact back-junction (BC-BJ) solar cells under illumination with high energy ultraviolet (UV) photons was investigated. The impact of the phosphorus doped front surface field (FSF) layer on the stability of the front surface passivation under UV illumination was investigated. Lifetime samples and solar cells without the front surface field showed a significant performance reduction when exposed to ultraviolet light. The surface saturation current density (J 0e) increased from 48 to 446fA/cm2 after the UV exposure. At the same time the efficiency of the BC-BJ solar cells without the FSF diffusion reduced from 19.8% to 14.3%. In contrast to the lifetime samples and solar cells without the FSF diffusion, the tested n+nn+ structures and the BC-BJ solar cells with applied FSF diffusion profiles were significantly more stable under UV exposure, i.e. J 0e increased only by a factor of 25% and the efficiency of these cells decreased only 0.3%abs by the UV illumination. Finally it was shown that the performance of the UV-degraded solar cells without FSF could be improved during a forming gas anneal (FGA). Due to application of FGA the efficiency almost fully recovered from 14.3% to 19.6%. [Copyright &y& Elsevier]

Abstract: The knowledge of the loss mechanisms in industrial back-contact back-junction (BC BJ) silicon solar cells and their dependence on geometrical and substrate parameters provides the opportunity to further increase the cell efficiency of this cell type. In the presented paper the influences of the different loss mechanisms on the cell parameters of BC BJ solar cells were analyzed. The basis of the simulations was an advanced 1-d model that regards the detrimental influences of intrinsic losses, optical losses, series resistance losses and recombination losses on the cell efficiency. In this context the main influence of electrical shading losses will be discussed in particular, due to the restrictions of the minimum base width as a result of industrial structuring processes. The predictions of the theoretical calculations will be compared with the measured cell parameters of BC BJ solar cells for various cell designs. In order to further improve the cell design the influences of geometrical parameters (pitch, base width) and substrate parameters (base resistivity) on the cell efficiency will be analyzed. The modeling data show that the optimum cell geometry defines a balance between series resistance and electrical shading losses. [Copyright &y& Elsevier]

Abstract: Phase control is critical for achieving high-performance CdTe cells when Cu x Te is used as a back-contact for CdTe cells. Cu x Te phases are mainly controlled by the Cu/Te ratio, and they can also be affected by post-heat-treatment temperature. Although Cu2Te has the highest conductivity, it is unstable and provides more Cu diffusion into the CdS and CdTe films. Cu diffusion into the CdS causes “cross-over”, and Cu diffusion into the CdTe film creates Cu-related defects that lower photogenerated carrier lifetime and result in voltage-dependent collection. A “recontact” experiment clearly indicated that the mechanism giving rise to “roll-over” is the formation of Cu-related oxides, rather than the loss of Cu on the back-contact. [Copyright &y& Elsevier]

ZnTe/ZnTe:Cu complex layers deposited by vacuum co-evaporation have been introduced to CdS/CdTe solar cells. The C-V and I-V curves have been investigated and the effects of un-doped ZnTe layer thickness as well as annealing temperatures on I-V characteristics of CdTe solar cells have been studied. The results show that the “roll over” and “cross over” phenomena of dark and light I-V curves can be eliminated by use of ZnTe/ZnTe:Cu layer and the fill factor for a typical sample has increased to 73%, where there is no high resistance transparent layer. The reasons have been discussed combined with the energy band diagram of CdTe solar cells. [ABSTRACT FROM AUTHOR]

Back-contact design for the architecture of devices is a promising approach to develop high-performance perovskite solar cells. Here, numerical simulation methods are used to investigate device properties of back-contact perovskite solar cells (BC–PSCs) with the quasi-interdigitated, flat-interdigitated, and interdigitated electrode designs. The results highlight the principal differences in the designs of the electrodes and provide an investigation and analysis of the impact of these electrodes on the photovoltaic properties of their BC-PSCs. The effect of the perovskite photoactive layer electronic properties on the performance of BC-PSCs is also investigated. It is revealed that while BC-PSCs with the quasi-interdigitated electrode design can potentially produce power conversion efficiencies (PCEs) well above 25 %, BC-PSCs with the flat-interdigitated and interdigitated electrode designs are more tolerant to electronic imperfections in the perovskite layer and can produce PCEs higher than those in devices with the quasi-interdigitated electrode design. Manufacturing and prospective use of electrodes with the quasi-interdigitated, flat-interdigitated, and interdigitated designs in developing BC-PSCs are discussed from the experimental standpoint. • Numerical simulations are employed to investigate device properties of back-contact perovskite solar cells with various device designs. • Back-contact perovskite solar cells with quasi-interdigitated electrodes could give >25 % efficiency under optimal conditions. • Devices with flat quasi-interdigitated and interdigitated electrodes are more tolerant to imperfections in the perovskite layer. • The findings of this work can be used for designing back-contact perovskite solar devices with the best performance. [ABSTRACT FROM AUTHOR]

Perovskite solar cells are by far the photovoltaic technology with the fastest efficiency evolution, reaching now the astonishing power conversion efficiency (PCE) of 25.2%. Their advantages cover also color and transparency, extremely low thickness, low cost, simple fabrication methods and versatile designs. Nevertheless, since it is a young technology, there are still several challenges that need to be overcome for making its commercialization feasible. For making perovskite solar modules, the back-contact plays a critical job since it drives and deliveries the low energy electrons to the p contact of the cell. In n-i-p configuration cells, gold is normally used as back-contact, which is expensive and rare. In this work, several commercial carbon papers and application procedures were investigated. The best performing system produced 89% of the PCE obtained with standard gold back-contact. Besides having a much simpler and cheaper application method, other features such as low cost, great chemical and mechanical stability and low electrical resistivity proved carbon papers potential for commercialization. Moreover, when a gold interlayer of 5 nm was applied, the relative PCE increased up to 92%. Image 1 • A PCE record value is reported for a PSC with a carbon paper back-contact. • The application method of the novel carbon back-contact is extremely simple. • The carbon paper features low sheet resistance (0.5 Ω/sq) and near ohmic contact. • A gold thin layer was used to enhance charge extraction at the back-contact. [ABSTRACT FROM AUTHOR]

Carbon nanofibers (CNFs) based thin films were introduced as a buffer layer in the back contact of of CdTe thin film solar cells. CNFs buffer layer is used to replace the conventional metal contact layer. Quantitative band alignment measurement by using X-ray photoelectron spectroscopy (XPS) demonstrated that a relatively low energy barrier at the CNF/CdTe interface was formed. The valance band offset of 0.47 eV and conduction band offset of 0.80 eV were examined between CNF and CdTe.. The stability of CdTe solar cells was considerably improved by introducing CNF buffer layer with trace amount of Cu to fabricate low-energy barrier back contact. The CNFs as a buffer layer between CdTe and metal Au electrode based fabricated CdTe thin film solar cells demonstrated a conversion efficiency of 11.4 %. From the device stability stressing tests we conclude that CNFs as a buffer layer in a CdTe thin film solar cell meaningfully improved the cell performance and device stability. [ABSTRACT FROM AUTHOR]

The perovskite solar cells with back-contact structure was reported recently that its carriers have a good diffusion length of 12 μm, which was considered as an innovational way to improve the cell's power conversion efficiency (PCE). Based on this reported experiment, the diffusion and drift of photogenerated carriers of the back-contact structure perovskite solar cell are calculated here detailly. Furthermore, the influence of carrier diffusion length, geometric scale, position of back-contact buried gate, and structure of the cell on performance is analyzed. The results showed that the PCE of a modified back-contact perovskite solar cell is superior to that of reported back-contact structure cell and traditional p-i-n structure cell under the same material parameters. It shows that the modified back-contact perovskite solar cell with optimized parameters achieved PCE of 28.27 %. [ABSTRACT FROM AUTHOR]

Lithography-free interdigitated back-contact silicon heterojunction (IBC-SHJ) solar cells with dopant-free metal oxides (TiO 2 and MoO x) as the carriers selective transport layers were investigated. Spin-coating and hot-wire reactive-sublimation deposition together with low cost mask technology were used to fabricate the solar cells. Insertion of a SiO x layer with the thickness of about 2.4 nm between the intrinsic amorphous Si (a-Si:H(i)) passivation layer and the spin-coated TiO 2 layer greatly improves the solar cell performance due to the enhanced field-effect passivation of the a-Si:H(i)/SiO x /TiO 2 layer stack. Efficiency up to 20.24% was achieved on the lithography-free and dopant-free IBC-SHJ devices with a-Si:H(i)/SiO x /TiO 2 layer stack as the electron selective transport layer, a-Si:H(i)/MoO x as the hole selective transport layer, and WO x as the antireflection layer. The novel IBC-SHJ solar cells show significant advantages in simplification of the technology and process compared with the IBC-SHJ devices whose back surface pattering and carrier selective layers relied on photolithography and plasma enhanced chemical vapor deposition (PECVD). • An a-Si:H(i)/SiO x /TiO 2 layer stack was used as the efficient electron selective transport layer with spin-coated TiO 2. • The hot-wire reactive-sublimation deposited MoO x was used as the hole selective transport layer. • An efficiency of 20.24% is finally achieved on a lithography-free back-contact SHJ device. [ABSTRACT FROM AUTHOR]