Search

Effectively incorporating alkali metals or alternative isovalent cations into Cu2ZnSnS4 (CZTS) is considered one of the most promising strategies for realizing a step‐change improvement in the photovoltaic device performance. Herein, the local distribution of Na and Cd by a moisture‐assisted postdeposition annealing (MAPDA) treatment combined with a subsequent heterojunction heat treatment is manipulated. The MAPDA treatment facilitates the controllable reduction of the Na concentration, thus promoting the spontaneous diffusion of Cd into the heterojunction region. A subsequent 150 °C low‐temperature heterojunction heat treatment after MAPDA treatment enables further modification of Cd and Na distributions, leading to significantly enhanced optoelectronic properties at the CZTS/CdS heterojunction and greatly improved device performance with a peak conversion efficiency of 9.40%. The modified heterojunction significantly improves quasi‐Fermi‐level splitting under low‐photon injection, making CZTS solar cells more feasible in low‐light applications. This work provides an effective approach to simultaneously manipulate the distribution of Na and Cd, enabling pronounced modification of the heterojunction quality of CZTS solar cells and boost of conversion efficiencies. Insights gleaned herein may also be applicable to manipulating other critical trace elements in chalcogenide materials in general. [ABSTRACT FROM AUTHOR]

Sulfide kesterite Cu2ZnSnS4 (CZTS) solar cells, containing earth‐abundant and environmentally benign constituents, are regarded as promising candidates for thin‐film photovoltaic technologies. CZTS device performance, however, is currently limited by severe nonradiative recombination caused by abundant deep‐level defects. Herein, an effective defect engineering approach for high bandgap CZTS solar cells using a newly introduced moisture‐assisted post‐deposition annealing treatment is reported. This treatment modifies the local chemical composition within the heterojunction and CZTS grain boundaries and enhances the incorporation of Cd within the CZTS layer during CdS deposition. Cd not only accumulates at the grain boundaries, but it also presents in grain interiors where it occupies Cu lattice sites. The overall modification of the local chemical environment suppresses deep level defects and activates relatively shallow acceptor CuZn antisites and Cu vacancies, giving rise to remarkably improved device performance. This work opens a new direction for defect engineering of kesterite materials, which may also be applicable to other thin film semiconductors. [ABSTRACT FROM AUTHOR]

The earth‐abundant and environmentally‐friendly CuSbS2 solar cells have been struggling with low device performance, especially poor open circuit voltage (Voc). In this work, post‐annealing treatment of the CuSbS2/CdS heterojunction performed on CuSbS2‐based solar cells was firstly reported. With this treatment, we demonstrated CuSbS2 solar cells with a record Voc of 622 mV. The improvement of device performance was found peaked at 250°C post‐annealing which mainly benefits from the significantly boosted open‐circuit voltage and short‐circuit current. The study of microstructure by high‐resolution transmission electron microscopy revealed that such improvement could be attributed to the formation of epitaxial CuSbS2/CdS hetero‐interface upon heat treatment, which reduces the interface defect density that may lead to reduced Voc deficit. Besides, results of photoluminescence and time‐resolved photoluminescence measurements also indicated improved electrical properties of completed devices with higher photoluminescence intensity and longer minority carrier lifetime. We demonstrated significant improvement in efficiency (particularly in the Voc and Jsc) for CuSbS2 solar cells by post‐heat treatment of the CuSbS2/CdS heterojunction. The underlying correlation between post‐heat treatment and device performance reveals that the post‐heat treatment on the heterojunction leads to (1) the transformation from amorphous to epitaxial relationship of CuSbS2/CdS hetero‐interface and (2) simultaneously improved absorber quality. [ABSTRACT FROM AUTHOR]

Abstract: Planar perovskite solar cells obtained by low‐temperature solution processing are of great promise, given a high compatibility with flexible substrates and perovskite‐based tandem devices, whilst benefitting from relatively simple manufacturing methods. However, ionic defects at surfaces usually cause detrimental carrier recombination, which links to one of dominant losses in device performance, slow transient responses, and notorious hysteresis. Here, it is shown that several different types of ionic defects can be simultaneously passivated by simple inorganic binary alkaline halide salts with their cations and anions. Compared to previous literature reports, this work demonstrates a promising passivation technology for perovskite solar cells. The efficient defect passivation significantly suppresses the recombination at the SnO2/perovskite interface, contributing to an increase in the open‐circuit voltage, the fast response of steady‐state efficiency, and the elimination of hysteresis. By this strong leveraging of multiple‐element passivation, low‐temperature‐processed, planar‐structured perovskite solar cells of 20.5% efficiencies, having negligible hysteresis, are obtained. Moreover, this defect‐passivation enhances the stability of solar cells with efficiency beyond 20%, retaining 90% of their initial performance after 30 d. This approach aims at developing the concept of defect engineering, which can be expanded to multiple‐element passivation from monoelement counterparts using simple and low‐cost inorganic materials. [ABSTRACT FROM AUTHOR]

A PbSe quantum dot solar cell with an efficiency of 7.22% and a fill factor of 62.4% is achieved by applying a CsPbBr3 perovskite quantum dot back layer. The back layer can effectively suppress carrier recombination at the PbSe/Au interfaces, hence lead to significant improvement in open‐circuit voltage and fill factor. [ABSTRACT FROM AUTHOR]

We report a reproducible enhancement of the open circuit voltage in Cu2ZnSnS4 solar cells by introduction of a very thin CeO2 interlayer between the Cu2ZnSnS4 absorber and the conventional CdS buffer. CeO2, a non-toxic earth-abundant compound, has a nearly optimal band alignment with Cu2ZnSnS4 and the two materials are lattice-matched within 0.4%. This makes it possible to achieve an epitaxial interface when growing CeO2 by chemical bath deposition at temperatures as low as 50℃. The open circuit voltage improvement is then attributed to a decrease in the interface recombination rate through formation of a high-quality heterointerface. [ABSTRACT FROM AUTHOR]

Sulfurization with various atmosphere and postheat treatments has been reported for earth abundant kesterite Cu2ZnSnS4 (CZTS) preparation as cost-effective material for next-generation solar cells. A full understanding of the nanoscale microstructure and chemistry of CZTS/CdS interface obtained from these different fabrication routes is currently lacking, yet is critical to developing optimal processing routes for high-performance kesterite solar cells. Here, the first detailed investigation of the interfacial microstructure and chemistry of CdS/Cu2ZnSnS4 heterojunctions is presented. For CZTS obtained from sulfurization in a sulfur-only atmosphere where highly defective surfaces are present, air annealing followed by etching in the initial stage of chemical bath deposition (CBD) process can effectively eliminate interfacial defects and allow the epitaxial growth of CBD-CdS, improving the minority lifetime, open circuit voltage ( VOC), and fill factor (FF) of the devices, while blocking Cd diffusion and deteriorating short circuit current ( Jsc). For CZTS from sulfurization in a combined sulfur and SnS atmosphere where CBD-CdS can directly epitaxially grow on CZTS and Cd-diffusion is clearly observed, associated devices show the longest lifetime and the highest efficiency of 8.76%. Epitaxial growth of CdS and Cd diffusion into CZTS are found to be two crucial features minimizing interfacial recombination and achieving high-efficiency devices. This will not only enhance the understanding of the device structure and physics of kesterite based solar cells, but also provide an effective way for designing other chalcogenide heterojunction solar cells. [ABSTRACT FROM AUTHOR]

A kesterite Cu2ZnSnS4 thin film solar cell with efficiency of over 9% is obtained by utilizing Zn1–xCdxS film as a replacement to traditional CdS buffer layer. Zn1–xCdxS film can optimize the conduction band offset between Cu2ZnSnS4 absorber and buffer, forming a minor positive conduction band alignment, thereby alleviating the recombination significantly and improving the open circuit voltage and fill factor efficiently. [ABSTRACT FROM AUTHOR]

While interfacial and grain‐boundary passivation presently attract enormous research interest for perovskite solar cells (PSCs), the improvement of Cs‐(FAPbI3)X(MAPbBr3)Y bulk quality still lacks systematical study, especially for constructing polycrystalline layers in planar configurations. Here, a DMSO‐molecule‐process for improving the quality of Cs‐(FAPbI3)0.85(MAPbBr3)0.15 is developed, where the molar ratio of precursors, the kind of anti‐solvents, and speed‐time profiles are found critical. The optimized treatment significantly enhanced the crystal orientation, grain size, surface roughness, photo‐response, carrier lifetime, and contact potential difference of absorbers. Cs‐(FAPbI3)0.85(MAPbBr3)0.15 absorbers also present superior charge transport, as well as reduced carrier recombination and decreased trap densities via DMSO‐molecule‐control, enabling performance improvement on both long‐term stability and photovoltaic parameters of 1 cm2 PSCs. Champion planar cells demonstrated a power conversion efficiency (PCE) of 21.07% (0.159 cm2) and PCE of 19.4% (1 cm2) with negligible hysteresis. Moreover, 1 cm2 devices retained 90% of initial PCE after aging 50 days in ambient air. DMSO‐molecule‐control is demonstrated to enhance the morphological and electronic qualities of Cs‐(FAPbI3)0.85(MAPbBr3)0.15 absorbers, thus increasing the efficiency (reaching 19.4%) and boosting the long‐term stability (retaining 90% of the initial efficiency after 50 days in ambient air) of 1 cm2 sized planar perovskite solar cells. [ABSTRACT FROM AUTHOR]

Hybrid metal halide perovskite solar cells (PSCs) are the most promising candidates to share the future energy market with silicon solar cells thanks to their excellent photovoltaic (PV) properties in single junction and tandem applications. Although PSCs are already highly efficient, their performance can be further improved by passivating the perovskite boundaries and improving current-voltage hysteresis. Here, we implement a double-sided passivation approach to enhance the performance of n-i-p structured PSCs, showing how passivating on either side improves cell performance. The electron-collecting side was passivated with biphenyl-4,4 -dicarboxylic acid (BPDC), and n-octyl ammonium bromide was used to passivate the hole-collecting side. The power conversion efficiency of the champion cell improved from 18.7 % for control to 20.9 % when double-sided passivation was implemented. Surface imaging showed how the surface boundaries improved following passivation, resulting in better open circuit voltages (V OC) and fill factors. In addition, passivation creates a barrier for ion migration, improving J-V hysteresis and stability in the process. The champion cell displayed a V OC of 1192 mV with double-sided passivation, incurring only ∼390 mV loss, thereby achieving a high V OC with a mid-bandgap perovskite. Preliminary degradation testing in ambient conditions shows that double-sided passivation also improves the stability of the cells by impeding ion migration. • Low-cost double-sided passivation of perovskite solar cells improved perovskite surface and PV performance by 11.7 %. • Biphenyl-4,4 -dicarboxylic acid used for the first time to passivate perovskite solar cells. • Passivation created a barrier to migrating ions, reducing intrinsic degradation and J-V hysteresis. • Open circuit voltage was raised with passivation, double-sided passivation only incurred 390 mV photovoltage loss. [ABSTRACT FROM AUTHOR]

In this work we report the Na incorporation from Na-doped Mo (Mo-Na) back contact for kesterite Cu 2 ZnSnS 4 solar cells on flexible stainless steel substrates. It is demonstrated that Na can be effectively incorporated into CZTS by inserting Mo-Na layer at back contact. Direct contact of CZTS and Mo-Na layer leads to poor homogeneity and adhesion. The thickness of MoS 2 formed at the back contact depends on the presence of Na and whether Mo contacts with CZTS directly. Back contact configuration with a Mo capping layer on Mo-Na layer is found to be helpful to maintain the advantages of Mo back contact and control the thickness of MoS 2 interface. As a result, CZTS device fabricated on this configuration yields higher conversion efficiency of 6.2%. However, this efficiency is still far lower than that on traditional soda lime glass substrate which shows efficiency over 8%. The loss mechanism of device fabricated on stainless steel is investigated and analyzed according to the device performance and electrical parameters. [ABSTRACT FROM AUTHOR]

Short minority carrier lifetime and low open circuit voltage (Voc) are key issues limiting the current efficiency development for Cu 2 ZnSnS 4 (CZTS) thin film solar cells. This work presents the use of Cd ion soaking and post-heat treatment to increase the lifetime and Voc of CZTS. The time-resolved photoluminescence (TRPL) results confirmed that Cd ion soaking and post heat treatment is effective in enhancing the minority lifetime, from ∼10 ns up to ∼28 ns. With analyses of the current density- voltage (J-V) curves and external quantum efficiency (EQE) data, Cd ion soaking and subsequent post heat treatment is found to greatly reduce the recombination and improve the junction quality, contributing to a ∼70 mV Voc enhancement and resulting in the increased device efficiency of 7.6%, from 5.9%. [ABSTRACT FROM AUTHOR]

The large open circuit voltage (Voc) deficit (Eg/ q -Voc) is the key factor limiting the current efficiency of pure sulfide Cu 2 ZnSnS 4 (CZTS) thin film solar cells. This present work reports CZTS devices with a Voc of over 710 mV by utilizing either In 2 S 3 buffer or In 2 S 3 /CdS hybrid buffer. The improvement in Voc mainly results from (i) an increased carrier concentration in CZTS due to In-doping when the In 2 S 3 buffer is adjacent to the CZTS absorber and (ii) favorable conduction band alignments at the CZTS/buffer interface. However, devices with In 2 S 3 buffers suffer from having a lower Fill Factor (FF) and short circuit current density (Jsc) when compared with those with CdS buffers. In contrast devices with In 2 S 3 /CdS hybrid buffers not only yield an enhancement in Voc, but also give the same level of FF and an even higher Jsc relative to CdS buffers, thereby increasing the efficiency from 5.5% to 6.6%. These hybrid In 2 S 3 /CdS buffers provide a promising way to reduce the Voc deficit and further boost the efficiency of pure sulfide CZTS solar cells. [ABSTRACT FROM AUTHOR]

Highlights: [•] The Mo/Zn/(Cu & Sn) metallic structure was utilized to fabricate CZTS solar cell. [•] Found that Zn rich composition facilitate the formation of large grain. [•] Sn composition is highly correlated Cu content with Cu/Sn ratio of two. [Copyright &y& Elsevier]