Current transport studies of amorphous n/p junctions and its application in a‐Si:H/HIT‐type tandem cells

This paper presents an understanding of the fundamental carrier transport mechanism in hydrogenated amorphous silicon (a‐Si:H)‐based n/p junctions. These n/p junctions are, then, used as tunneling and recombination junctions (TRJ) in tandem solar cells, which were constructed by stacking the a‐Si:H‐based solar cell on the heterojunction with intrinsic thin layer (HIT) cell. First, the effect of activation energy (E_a) and Urbach parameter (E_u) of n‐type hydrogenated amorphous silicon (a‐Si:H(n)) on current transport in an a‐Si:H‐based n/p TRJ has been investigated. The photoluminescence spectra and temperature‐dependent current–voltage characteristics in dark condition indicates that the tunneling is the dominant carrier transport mechanism in our a‐Si:H‐based n/p‐type TRJ. The fabrication of a tandem cell structure consists of an a‐Si:H‐based top cell and an HIT‐type bottom cell with the a‐Si:H‐based n/p junction developed as a TRJ in between. The development of a‐Si:H‐based n/p junction as a TRJ leads to an improved a‐Si:H/HIT‐type tandem cell with a better open circuit voltage (V_oc), fill factor (FF), and efficiency. The improvements in the cell performance was attributed to the wider band‐tail states in the a‐Si:H(n) layer that helps to an enhanced tunneling and recombination process in the TRJ. The best photovoltage parameters of the tandem cell were found to be V_oc = 1430 mV, short circuit current density = 10.51 mA/cm², FF = 0.65, and efficiency = 9.75%. Copyright © 2015 John Wiley & Sons, Ltd.     

High potential of thin (<1 µm) a‐Si: H/µc‐Si:H tandem solar cells

Silicon based thin tandem solar cells were fabricated by plasma enhanced chemical vapor deposition (PECVD) in a 30 × 30 cm² reactor. The layer thicknesses of the amorphous top cells and the microcrystalline bottom cells were significantly reduced compared to standard tandem cells that are optimized for high efficiency (typically with a total absorber layer thickness from 1.5 to 3 µm). The individual absorber layer thicknesses of the top and bottom cells were chosen so that the generated current densities are similar to each other. With such thin cells, having a total absorber layer thickness varying from 0.5 to 1.5 µm, initial efficiencies of 8.6–10.7% were achieved. The effects of thickness variations of both absorber layers on the device properties have been separately investigated. With the help of quantum efficiency (QE) measurements, we could demonstrate that by reducing the bottom cell thickness the top cell current density increased which is addressed to back‐reflected light. Due to a very thin a‐Si:H top cell, the thin tandem cells show a much lower degradation rate under continuous illumination at open circuit conditions compared to standard tandem and a‐Si:H single junction cells. We demonstrate that thin tandem cells of around 550 nm show better stabilized efficiencies than a‐Si:H and µc‐Si:H single junction cells of comparable thickness. The results show the high potential of thin a‐Si/µc‐Si tandem cells for cost‐effective photovoltaics. Copyright © 2010 John Wiley & Sons, Ltd.     

High efficiency triple junction thin film silicon solar cells with optimized electrical structure

We report on improving the performance of pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells and corresponding single‐junction solar cells in this paper. Based on wet‐etching sputtered aluminum‐doped zinc oxide (ZnO:Al) substrates with optimized surface morphologies and photo‐electrical material properties, after adjusting individual single‐junction solar cells utilized in triple‐junction solar cells with various optimization techniques, we pay close attention to the optimization of tunnel recombination junctions (TRJs). By means of the optimization of individual a‐Si:H/a‐SiGe:H and a‐SiGe:H/µc‐Si:H double‐junction solar cells, we compensated for the open circuit voltage (V_oc) loss at the a‐Si:H/a‐SiGe:H TRJ by adopting a p‐type µc‐Si:H layer with a low activation energy. By combining the optimized single‐junction solar cells and top/middle, middle/bottom TRJs with little electrical losses, an initial efficiency of 15.06% was achieved for pin‐type a‐Si:H/a‐SiGe:H/µc‐Si:H triple‐junction solar cells. Copyright © 2014 John Wiley & Sons, Ltd.     

2D/3D Heterostructure for Semitransparent Perovskite Solar Cells with Engineered Bandgap Enables Efficiencies Exceeding 25% in Four‐Terminal Tandems with Silicon and CIGS

Wide‐bandgap perovskite solar cells (PSCs) with optimal bandgap (E_g) and high power conversion efficiency (PCE) are key to high‐performance perovskite‐based tandem photovoltaics. A 2D/3D perovskite heterostructure passivation is employed for double‐cation wide‐bandgap PSCs with engineered bandgap (1.65 eV ≤ E_g ≤ 1.85 eV), which results in improved stabilized PCEs and a strong enhancement in open‐circuit voltages of around 45 mV compared to reference devices for all investigated bandgaps. Making use of this strategy, semitransparent PSCs with engineered bandgap are developed, which show stabilized PCEs of up to 25.7% and 25.0% in four‐terminal perovskite/c‐Si and perovskite/CIGS tandem solar cells, respectively. Moreover, comparable tandem PCEs are observed for a broad range of perovskite bandgaps. For the first time, the robustness of the four‐terminal tandem configuration with respect to variations in the perovskite bandgap for two state‐of‐the‐art bottom solar cells is experimentally validated.     

Interface Molecular Engineering for Laminated Monolithic Perovskite/Silicon Tandem Solar Cells with 80.4% Fill Factor

A multipurpose interconnection layer based on poly(3,4‐ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT:PSS), and d ‐sorbitol for monolithic perovskite/silicon tandem solar cells is introduced. The interconnection of independently processed silicon and perovskite subcells is a simple add‐on lamination step, alleviating common fabrication complexities of tandem devices. It is demonstrated experimentally and theoretically that PEDOT:PSS is an ideal building block for manipulating the mechanical and electrical functionality of the charge recombination layer by controlling the microstructure on the nano‐ and mesoscale. It is elucidated that the optimal functionality of the recombination layer relies on a gradient in the d ‐sorbitol dopant distribution that modulates the orientation of PEDOT across the PEDOT:PSS film. Using this modified PEDOT:PSS composite, a monolithic two‐terminal perovskite/silicon tandem solar cell with a steady‐state efficiency of 21.0%, a fill factor of 80.4%, and negligible open circuit voltage losses compared to single‐junction devices is shown. The versatility of this approach is further validated by presenting a laminated two‐terminal monolithic perovskite/organic tandem solar cell with 11.7% power conversion efficiency. It is envisioned that this lamination concept can be applied for the pairing of multiple photovoltaic and other thin film technologies, creating a universal platform that facilitates mass production of tandem devices with high efficiency.     

Preparation and measurement of highly efficient a‐Si:H single junction solar cells and the advantages of μc‐SiOx:H n‐layers

Reducing the optical losses and increasing the reflection while maintaining the function of doped layers at the back contact in solar cells are important issues for many photovoltaic applications. One approach is to use doped microcrystalline silicon oxide (μc‐SiO_x:H) with lower optical absorption in the spectral range of interest (300 nm to 1100 nm). To investigate the advantages, we applied the μc‐SiO_x:H n‐layers to a‐Si:H single junction solar cells. We report on the comparison between amorphous silicon (a‐Si:H) single junction solar cells with either μc‐SiO_x:H n‐layers or non‐alloyed silicon n‐layers. The origin of the improved performance of a‐Si:H single junction solar cells with the μc‐SiO_x:H n‐layer is identified by distinguishing the contributions because of the increased transparency and the reduced refractive index of the μc‐SiO_x:H material. The solar cell parameters of a‐Si:H solar cells with both types of n‐layers were compared in the initial state and after 1000 h of light soaking in a series of solar cells with various absorber layer thicknesses. The measurement procedure for the determination of the solar cell performance is described in detail, and the measurement accuracy is evaluated and discussed. For an a‐Si:H single junction solar cell with a μc‐SiO_x:H n‐layer, a stabilized efficiency of 10.3% after 1000 h light soaking is demonstrated. Copyright © 2015 John Wiley & Sons, Ltd.     

Performance enhancement of III–V compound multijunction solar cell incorporating transparent electrode and surface treatment

To enhance the performance of tandem‐type III–V compound multijunction solar cells, the transparent indium‐tin‐oxide (ITO) film was used to replace conventional metal electrode for increasing the incident light area. For performing ohmic contact between the n‐AlInP window layer and the ITO film, a transition layer of Au/AuGeNi thin metals was used and investigated. Besides, to improve ohmic performance and to passivate the surface states, (NH₄)₂S_x surface treatment was used. The conversion efficiency of the (NH₄)₂S_x‐treated triple‐junction solar cells was increased more than 3.09%. Furthermore, an improved oblique SiO₂/SiO₂/ITO triple antireflection structure was designed to reduce the reflectivity of illuminating sunlight. The conversion efficiency of the (NH₄)₂S_x‐treated triple‐junction solar cell with improved antireflection structure could be improved more than 4.23%. Simple and effective approaches were designed to improve the performances of tandem‐type III–V triple‐junction solar cells. Copyright © 2010 John Wiley & Sons, Ltd.     

27%‐Efficiency Four‐Terminal Perovskite/Silicon Tandem Solar Cells by Sandwiched Gold Nanomesh

Multijunction/tandem solar cells have naturally attracted great attention because they are not subject to the Shockley–Queisser limit. Perovskite solar cells are ideal candidates for the top cell in multijunction/tandem devices due to the high power conversion efficiency (PCE) and relatively low voltage loss. Herein, sandwiched gold nanomesh between MoO₃ layers is designed as a transparent electrode. The large surface tension of MoO₃ effectively improves wettability for gold, resulting in Frank–van der Merwe growth to produce an ultrathin gold nanomesh layer, which guarantees not only excellent conductivity but also great optical transparency, which is particularly important for a multijunction/tandem solar cell. The top MoO₃ layer reduces the reflection at the gold layer to further increase light transmission. As a result, the semitransparent perovskite cell shows an 18.3% efficiency, the highest reported for this type of device. When the semitransparent perovskite device is mechanically stacked with a heterojunction silicon solar cell of 23.3% PCE, it yields a combined efficiency of 27.0%, higher than those of both the sub‐cells. This breakthrough in elevating the efficiency of semitransparent and multijunction/tandem devices can help to break the Shockley–Queisser limit.     

Comparative life‐cycle energy payback analysis of multi‐junction a‐SiGe and nanocrystalline/a‐Si modules

Despite the publicity of nanotechnologies in high tech industries including the photovoltaic sector, their life‐cycle energy use and related environmental impacts are understood only to a limited degree as their production is mostly immature. We investigated the life‐cycle energy implications of amorphous silicon (a‐Si) PV designs using a nanocrystalline silicon (nc‐Si) bottom layer in the context of a comparative, prospective life‐cycle analysis framework. Three R&D options using nc‐Si bottom layer were evaluated and compared to the current triple‐junction a‐Si design, i.e., a‐Si/a‐SiGe/a‐SiGe. The life‐cycle energy demand to deposit nc‐Si was estimated from parametric analyses of film thickness, deposition rate, precursor gas usage, and power for generating gas plasma. We found that extended deposition time and increased gas usages associated to the relatively high thickness of nc‐Si lead to a larger primary energy demand for the nc‐Si bottom layer designs, than the current triple‐junction a‐Si. Assuming an 8% conversion efficiency, the energy payback time of those R&D designs will be 0.7–0.9 years, close to that of currently commercial triple‐junction a‐Si design, 0.8 years. Future scenario analyses show that if nc‐Si film is deposited at a higher rate (i.e., 2–3 nm/s), and at the same time the conversion efficiency reaches 10%, the energy‐payback time could drop by 30%. Copyright © 2010 John Wiley & Sons, Ltd.     

Life‐cycle assessment of photovoltaic modules: Comparison of mc‐Si,InGaP and InGaP/mc‐Si solar modules

A higher conversion efficiency of photovoltaic modules does not automatically imply a lower environmental impact, when the life‐cycle of modules is taken into account. An environmental comparison is carried out between the production and use phase, except maintenance, of an indium–gallium–phosphide (InGaP) on multicrystalline silicon (mc‐Si) tandem module, a thin‐film InGaP cell module and a mc‐Si module. The evaluation of the InGaP systems was made for a very limited industrial production scale. Assuming a fourfold reuse of the GaAs substrates in the production of the thin‐film InGaP (half) modules, the environmental impacts of the tandem module and of the thin‐film InGaP module are estimated to be respectively 50 and 80% higher than the environmental impact of the mc‐Si module. The energy payback times of the tandem module, the thin‐film InGaP module and the mc‐Si module are estimated to be respectively 5.3, 6.3 and 3.5 years. There are several ways to improve the life‐cycle environmental performance of thin‐film InGaP cells, including improved materials efficiency in production and reuse of the GaAs wafer and higher energy efficiency of the metalorganic chemical vapour deposition process. Copyright © 2003 John Wiley & Sons, Ltd.     

Low‐Bandgap Mixed Tin‐Lead Perovskites and Their Applications in All‐Perovskite Tandem Solar Cells

Efficient organic–inorganic metal halide perovskite absorbers have gained tremendous research interest in the past decade due to their super optoelectronic properties and defect tolerance. Lead (Pb) halide perovskites enable highly efficient perovskite solar cells (PSCs) with a record power conversion efficiency (PCE) of over 23%. However, the energy bandgaps of Pb halide perovskites are larger than the optimal bandgap for single junction solar cells, governed by the Shockley–Queisser (SQ) radiative limit. Mixed tin (Sn)‐Pb halide perovskites have drawn significant attention, since their bandgap can be tuned to below 1.2 eV, which opens a door for fabricating all‐perovskite tandem solar cells that can break the SQ radiative limit. This review summarizes the development of low‐bandgap mixed Sn‐Pb PSCs and their applications in all‐perovskite tandem solar cells. Its aim is to facilitate the development of new approaches to achieve high efficiency low‐bandgap single‐junction mixed Sn‐Pb PSCs and all‐perovskite tandem solar cells.     

Low-Dimensional 2-thiopheneethylammonium Lead Halide Capping Layer Enables Efficient Single-Junction Methylamine-Free Wide-Bandgap and Tandem Perovskite Solar Cells

Wide-bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open-circuit voltage (V_OC) deficit and serious photo-induced halide segregation remain the main challenges that impede their applications. Herein, a post-treatment strategy without thermal annealing is presented to form a 2D top layer of 2-thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing-free post-treatment method can more effectively passivate the defects of WBG methylamine (MA)-free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo-induced perovskite phase segregation, as compared with the thermal annealing method that yields multi-2D phases. The resulting opaque and semi-transparent 1.66 eV-bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small V_OC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA-free WBG PSCs. Consequently, four-terminal all-perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi-junction tandem solar cells.     

Thin film solar cells incorporating microcrystalline Si1–xGex as efficient infrared absorber: an application to double junction tandem solar cells

We have fabricated efficient (∼7–8%) hydrogenated microcrystalline Si_1–xGe_x (µc‐Si_1–xGe_x:H, x ∼ 0.1–0.17) single junction p‐i‐n solar cells with markedly higher short‐circuit current densities than for µc‐Si:H (x = 0) solar cells due to enhanced infrared absorption. By replacing the conventional µc‐Si:H with the µc‐Si_1–xGe_x:H as infrared absorber in double junction tandem solar cells, the bottom cell thickness can be reduced by more than half while preserving the current matching with hydrogenated amorphous silicon (a‐Si:H) top cell. An initial efficiency of 11.2% is obtained for a‐Si:H/µc‐Si₀.₉Ge₀.₁:H solar cell with bottom cell thickness less than 1 µm. Copyright © 2009 John Wiley & Sons, Ltd.     

DC‐sputtered ZnO:Al as transparent conductive oxide for silicon heterojunction solar cells with µc‐Si:H emitter

Silicon heterojunction (SHJ) solar cells are highly interesting, because of their high efficiency and low cost fabrication. So far, the most applied transparent conductive oxide (TCO) is indium tin oxide (ITO). The replacement of ITO with cheaper, more abundant and environmental friendly material with texturing capability is a promising way to reduce the production cost of the future SHJ solar cells. Here, we report on the fabrication of the SHJ solar cells with direct current‐sputtered aluminum‐doped zinc oxide (ZnO:Al) as an alternative TCO. Furthermore, we address several important differences between ITO and the ZnO:Al layers including a high Schottky barrier at the emitter/ZnO:Al interface and a high intrinsic resistivity of the ZnO:Al layers. To overcome the high Schottky barrier, we suggest employing micro‐crystalline silicon (µc‐Si:H) emitter, which also improves temperature threshold and passivation of the solar cell precursor. In addition, we report on the extensive studies of the effect of the ZnO:Al deposition parameters including layer thickness, oxygen flow, power density and temperature on the electrical properties of the fabricated SHJ solar cells. Finally, the results of our study indicate that the ZnO:Al deposition parameters significantly affect the electrical properties of the obtained solar cell. By understanding and fine‐tuning all these parameters, a high conversion efficiency of 19.2% on flat wafer (small area (5 × 5 mm²) and without any front metal grid) is achieved. Copyright © 2014 John Wiley & Sons, Ltd.     

Environmental life cycle assessment of roof‐integrated flexible amorphous silicon/nanocrystalline silicon solar cell laminate

This paper presents an environmental life cycle assessment of a roof‐integrated flexible solar cell laminate with tandem solar cells composed of amorphous silicon/nanocrystalline silicon (a‐Si/nc‐Si). The a‐Si/nc‐Si cells are considered to have 10% conversion efficiency. Their expected service life is 20 years. The production scale considered is 100 MW_p per year. A comparison of the a‐Si/nc‐Si photovoltaic (PV) system with the roof‐mounted multicrystalline silicon (multi‐Si) PV system is also presented. For both PV systems, application in the Netherlands with an annual insolation of 1000 kWh/m² is considered. We found that the overall damage scores of the a‐Si/nc‐Si PV system and the multi‐Si PV system are 0.012 and 0.010 Ecopoints/kWh, respectively. For both PV systems, the impacts due to climate change, human toxicity, particulate matter formation, and fossil resources depletion together contribute to 96% of the overall damage scores. Each of both PV systems has a cumulative primary energy demand of 1.4 MJ/kWh. The cumulative primary energy demand of the a‐Si/nc‐Si PV system has an uncertainty of up to 41%. For the a‐Si/nc‐Si PV system, an energy payback time of 2.3 years is derived. The construction for roof integration, the silicon deposition, and etching are found to be the largest contributors to the primary energy demand of the a‐Si/nc‐Si PV system, whereas encapsulation and the construction for roof integration are the largest contributors to its impact on climate change. Copyright © 2012 John Wiley & Sons, Ltd.     

Full‐wave optoelectrical modeling of optimized flattened light‐scattering substrate for high efficiency thin‐film silicon solar cells

The flattened light‐scattering substrate (FLiSS) is formed by a combination of two materials with a high refractive index mismatch, and it has a flat surface. A specific realization of this concept is a flattened two‐dimensional grating. When applied as a substrate for thin‐film silicon solar cells in the nip configuration, it is capable to reflect light with a high fraction of diffused component. Furthermore, the FLiSS is an ideal substrate for growing high‐quality microcrystalline silicon (µc‐Si:H), used as bottom cell absorber layer in most of multijunction solar cell architectures. FLiSS is a three‐dimensional structure; therefore, a full‐wave analysis of the electromagnetic field is necessary for its optimal implementation. Using finite element method, different shapes, materials, and geometrical parameters were investigated to obtain an optimized FLiSS. The application of the optimized FLiSS in µc‐Si:H single junction nip cell (1‐µm‐thick i‐layer) resulted in a 27.4‐mA/cm² implied photocurrent density. The absorptance of µc‐Si:H absorber exceeded the theoretical Yablonovitch limit for wavelengths larger than 750 nm. Double and triple junction nip solar cells on optimal FLiSS and with thin absorber layers were simulated. Results were in line with state‐of‐the‐art optical performance typical of solar cells with rough interfaces. After the optical optimization, a study of electrical performance was carried out by simulating current–voltage characteristics of nip solar cells on optimized FLiSS. Potential conversion efficiencies of 11.6%, 14.2%, and 16.0% for single, double, and triple junction solar cells with flat interfaces, respectively, were achieved. Copyright © 2012 John Wiley & Sons, Ltd.     

Improved conversion efficiency of a‐Si:H/µc‐Si:H thin‐film solar cells by using annealed Al‐doped zinc oxide as front electrode material

In recent years, zinc oxide has been investigated as a front electrode material in hydrogenated amorphous silicon/hydrogenated microcrystalline silicon (a‐Si:H/µc‐Si:H) tandem solar cells. Such as for other transparent conducting oxide materials and applications, a proper balancing of transparency and conductivity is necessary. The latter is directly related to the density and the mobility of charge carriers. A high density of charge carriers increases conductivity but leads to a higher absorption of light in the near‐infrared part of the spectrum due to increased free‐carrier absorption. Hence, the only way to achieve high conductivity while keeping the transparency as high as possible relies on an increase of carrier mobility. The carrier density and the mobility of sputtered Al‐doped zinc oxide (ZnO:Al) can be tailored by a sequence of different annealing steps. In this work, we implemented such annealed ZnO:Al films as a front electrode in a‐Si:H/µc‐Si:H tandem solar cells and compared the results with those of reference cells grown on as‐deposited ZnO:Al. We observed an improvement of short‐circuit current density as well as open‐circuit voltage and fill factor. The gain in current density could be attributed to a reduction of both sub‐band‐gap absorption and free‐carrier absorption in the ZnO:Al. The higher open‐circuit voltage and fill factor are indicators of a better device quality of the silicon for cells grown on annealed ZnO:Al. Altogether, the annealing led to an improved initial conversion efficiency of 12.1%, which was a gain of +0.7% in absolute terms. Copyright © 2013 John Wiley & Sons, Ltd.     

Highly transparent modulated surface textured front electrodes for high‐efficiency multijunction thin‐film silicon solar cells

To further increase the efficiency of multijunction thin‐film silicon (TF‐Si) solar cells, it is crucial for the front electrode to have a good transparency and conduction, to provide efficient light trapping for each subcell, and to ensure a suitable morphology for the growth of high‐quality silicon layers. Here, we present the implementation of highly transparent modulated surface textured (MST) front electrodes as light‐trapping structures in multijunction TF‐Si solar cells. The MST substrates comprise a micro‐textured glass, a thin layer of hydrogenated indium oxide (IOH), and a sub‐micron nano‐textured ZnO layer grown by low‐pressure chemical vapor deposition (LPCVD ZnO). The bilayer IOH/LPCVD ZnO stack guarantees efficient light in‐coupling and light trapping for the top amorphous silicon (a‐Si:H) solar cell while minimizing the parasitic absorption losses. The crater‐shaped micro‐textured glass provides both efficient light trapping in the red and infrared wavelength range and a suitable morphology for the growth of high‐quality nanocrystalline silicon (nc‐Si:H) layers. Thanks to the efficient light trapping for the individual subcells and suitable morphology for the growth of high‐quality silicon layers, multijunction solar cells deposited on MST substrates have a higher efficiency than those on single‐textured state‐of‐the‐art LPCVD ZnO substrates. Efficiencies of 14.8% (initial) and 12.5% (stable) have been achieved for a‐Si:H/nc‐Si:H tandem solar cells with the MST front electrode, surpassing efficiencies obtained on state‐of‐the‐art LPCVD ZnO, thereby highlighting the high potential of MST front electrodes for high‐efficiency multijunction solar cells. Copyright © 2015 John Wiley & Sons, Ltd.     

Simulation and fabrication of heterojunction silicon solar cells from numerical computer and hot‐wire CVD

In this paper, we will present a Pc1D numerical simulation for heterojunction (HJ) silicon solar cells, and discuss their possibilities and limitations. By means of modeling and numerical computer simulation, the influence of emitter‐layer/intrinsic‐layer/crystalline‐Si heterostructures with different thickness and crystallinity on the solar cell performance is investigated and compared with hot wire chemical vapor deposition (HWCVD) experimental results. A new technique for characterization of n‐type microcrystalline silicon (n‐µc‐Si)/intrinsic amorphous silicon (i‐a‐Si)/crystalline silicon (c‐Si) heterojunction solar cells from Pc1D is developed. Results of numerical modeling as well as experimental data obtained using HWCVD on µc‐Si (n)/a‐Si (i)/c‐Si (p) heterojunction are presented. This work improves the understanding of HJ solar cells to derive arguments for design optimization. Some simulated parameters of solar cells were obtained: the best results for J_sc = 39·4 mA/cm², V_oc = 0·64 V, FF = 83%, and η = 21% have been achieved. After optimizing the deposition parameters of the n‐layer and the H₂ pretreatment of solar cell, the single‐side HJ solar cells with J_sc = 34·6 mA/cm², V_oc = 0·615 V, FF = 71%, and an efficiency of 15·2% have been achieved. The double‐side HJ solar cell with J_sc = 34·8 mA/cm², V_oc = 0·645 V, FF = 73%, and an efficiency of 16·4% has been fabricated. Copyright © 2009 John Wiley & Sons, Ltd.     

Towards Efficient Integrated Perovskite/Organic Bulk Heterojunction Solar Cells: Interfacial Energetic Requirement to Reduce Charge Carrier Recombination Losses

Integrated perovskite/organic bulk heterojunction (BHJ) solar cells have the potential to enhance the efficiency of perovskite solar cells by a simple one‐step deposition of an organic BHJ blend photoactive layer on top of the perovskite absorber. It is found that inverted structure integrated solar cells show significantly increased short‐circuit current (J_sc) gained from the complementary absorption of the organic BHJ layer compared to the reference perovskite‐only devices. However, this increase in J_sc is not directly reflected as an increase in power conversion efficiency of the devices due to a loss of fill factor. Herein, the origin of this efficiency loss is investigated. It is found that a significant energetic barrier (≈250 meV) exists at the perovskite/organic BHJ interface. This interfacial barrier prevents efficient transport of photogenerated charge carriers (holes) from the BHJ layer to the perovskite layer, leading to charge accumulation at the perovskite/BHJ interface. Such accumulation is found to cause undesirable recombination of charge carriers, lowering surface photovoltage of the photoactive layers and device efficiency via fill factor loss. The results highlight a critical role of the interfacial energetics in such integrated cells and provide useful guidelines for photoactive materials (both perovskite and organic semiconductors) required for high‐performance devices.