Increase In Fill Factor Research Articles

One‐Pot Synthesis of Conjugation‐Extended Isomeric Dimer Acceptors for High‐Performance Q‑PHJ Solar Cells

AbstractEnd group modification is a crucial strategy for fine‐tuning non‐fullerene acceptors in organic solar cells (OSCs). Extending the conjugation of end groups enhances electron delocalization, promotes tighter intermolecular stacking, and improves crystallinity and spectral absorption. In this study, a series of isomeric dimer acceptors with conjugation‐extended end groups is synthesized to investigate how the position of end group extension affects the performance of dimers. Using a one‐pot Still coupling method, three dimers with inner end group extensions are efficiently synthesized, significantly reducing synthesis time and cost. Among these, the device based on dBSeIC‐ɛNIC exhibited a higher power conversion efficiency (PCE) compared to the dBSeIC‐γIC device, which lacks conjugated extension. Building on this, the connection site of the inner end group is optimized and extended the conjugation from the outer end group. As a result, the Q‐PHJ device using dBSeNIC‐γIC/PBQx‐H‐TF achieved a maximum PCE of 17.68%, largely due to a notable increase in fill factor (FF). The study reveals the critical impact of end group conjugation extension on dimer acceptor performance and underscores the importance of selecting the optimal connection site for enhancing OSC efficiency.

Fabrication of PSCs with light absorption chips utilizing double-metal-cladding waveguide technology

Metal nanoparticles or periodic metal nanostructures exhibit localized surface plasmon resonance (LSPR) effects, widely employed in photovoltaic devices to enhance the light absorption. In this study, we used a double-metal-cladding waveguide (DMCW) structure to fabricate hexagonal metal nanostructures on the front side of the indium tin oxide (ITO) glass, positioned away from the incident light direction. We then prepared perovskite solar cells under various reaction conditions. The analysis results indicate that the metal nanostructure chip excites near-field coupling, generating strong localized fields, and enhances the light absorption through the LSPR effect. The perovskite solar cells (PSCs) with the chip structures exhibited a significant increase in short-circuit current density (JSC) and fill factor (FF), accompanied by a decrease in dark current, indicating improved photovoltaic characteristics of the cells. Altering the evaporative deposition time of the silver film and the concentration of the reaction solution led to a 12.79% increase in the power conversion efficiency (PCE) of the PSCs.

(Sm3+/Eu3+/Tm3+)-TiO2 heterostructures for electrochemical and photovoltaic applications

This study reports on the synthesis of lanthanide oxides triply doped titania, forming a novel hetero-system known as (Sm3+/Eu3+/Tm3+)-TiO2. An environmentally friendly sol gel method was used to synthesize the energy-efficient (Sm3+/Eu3+/Tm3+)-TiO2, and thin films were deposited by spin coating. Electrode and solar cell devices were fabricated under ambient conditions, and rare earth doping enhanced the opto-electronic aspects of the host by narrowing the band gap up to 3.92, 3.85, and 3.56 eV. Particle sizes for the pure and doped materials were 85.15 and 82.72 nm, respectively. With a specific capacitance of 667.34 F g−1, the lanthanide-doped ornamented nickel foam electrode outperformed the pristine electrode, which had a specific capacitance of 169.59 F g−1. Moreover, this electrode exhibited tiny equivalent series resistance (Rs) of 0.13 Ω, indicating quicker response kinetics at the interface, in addition to its electrical double layer capacitance behavior. Electrochemical studies revealed that (Sm3+/Eu3+/Tm3+)-TiO2 semiconductor has a high specific power density of 8157.03 W kg−1, compared to 4079.73 W kg−1 for undoped titania. This improved specific power density demonstrates its suitability for practical scale applications. The produced materials were an excellent HER electro-catalyst with remarkably lower overpotential and Tafel slopes i.e., of 137 mV and 87.6 mV dec−1, in a respective manner, in comparison to the reference TiO2 with 147 mV and 104.5 mV dec−1, respectively. The electro-catalyst's response to the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) was enhanced upon lanthanide doping. Additionally, this substance successfully retrieved electrons from a perovskite solar cell device, achieving efficiency levels of 16.49 and 16.75 % in both forward and reverse bias with fill factor increase.

Development of high conducting phosphorous doped nanocrystalline thin silicon films for silicon heterojunction solar cells application

We have investigated the plasma-enhanced chemical vapor deposition growth of the phosphorus-doped hydrogenated nanocrystalline silicon (n-nc-Si:H) film as an electron-selective layer in silicon heterojunction (SHJ) solar cells. The effect of power densities on the precursor gas dissociation are investigated using optical emission spectra and the crystalline fraction in n-nc-Si:H films are correlated with the dark conductivity. With the P d of 122 mW cm−2 and ∼2% phosphorus doping, we observed Raman crystallinity of 53%, high dark conductivity of 43 S cm−1, and activation energy of ∼23 meV from the ∼30 nm n-nc-Si:H film. The n-nc-Si:H layer improves the textured c-Si surface passivation by two-fold to ∼2 ms compared to the phosphorus-doped hydrogenated amorphous silicon (n-a-Si:H) layers. An enhancement in the open-circuit voltage and external quantum efficiency (from >650 nm) due to the better passivation at the rear side of the cell after integrating the n-nc-Si:H layer compared to its n-a-Si:H counterpart. An improvement in the charge carrier transport is also observed with an increase in fill factor from ∼71% to ∼75%, mainly due to a reduction in electron-selective contact resistivity from ∼271 to ∼61 mΩ-cm2. Finally, with the relatively better c-Si surface passivation and carrier selectivity, a power conversion efficiency of ∼19.90% and pseudo-efficiency of ∼21.90% have been realized from the SHJ cells.

Ternary Polymer Solar Cells: Impact of Non-Fullerene Acceptors on Optical and Morphological Properties

Ternary organic solar cells contain a single three-component photoactive layer with a wide absorption window, achieved without the need for multiple stacking. However, adding a third component into a well-known binary blend can influence the energetics, optical window, charge carrier transport, crystalline order and conversion efficiency. In the form of binary blends, the low-bandgap regioregular polymer donor poly(3-hexylthiophene-2,5-diyl), known as P3HT, is combined with the acceptor PC61BM, an inexpensive fullerene derivative. Two different non-fullerene acceptors (ITIC and eh-IDTBR) are added to this binary blend to form ternary blends. A systematic comparison between binary and ternary systems was carried out as a function of the thermal annealing temperature of organic layers (100 °C and 140 °C). The power conversion efficiency (PCE) is improved due to increased fill factor (FF) and open-circuit voltage (Voc) for thermal-annealed ternary blends at 140 °C. The transport properties of electrons and holes were investigated in binary and ternary blends following a Space-Charge-Limited Current (SCLC) protocol. A favorable balanced hole–electron mobility is obtained through the incorporation of either ITIC or eh-IDTBR. The charge transport behavior is correlated with the bulk heterojunction (BHJ) morphology deduced from atomic force microscopy (AFM), contact water angle (CWA) measurement and 2D grazing-incidence X-ray diffractometry (2D-GIXRD).

SCAPS-1D simulated organometallic halide perovskites: A comparison of performance under Sub-Saharan temperature condition

Photovoltaic technology has been widely recognized as a means to advance green energy solutions in the sub-Saharan region. In the real-time operation of solar modules, temperature plays a crucial role, making it necessary to evaluate the thermal impact on the performance of the solar devices, especially in high-insolation environments. Hence, this paper investigates the effect of operating temperature on the performance of two types of organometallic halide perovskites (OHP) - formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). The solar cells were evaluated under a typical Nigerian climate in two different cities before and after graphene passivation. Using a one-dimensional solar capacitance simulation software (SCAPS-1D) program, the simulation results show that graphene passivation improved the conversion efficiency of the solar cells by 0.51 % (FASnI3 device) and 3.11 % (MAPbI3 device). The presence of graphene played a vital role in resisting charge recombination and metal diffusion, which are responsible for the losses in OHP. Thermal analysis revealed that the MAPbI3 device exhibited an increased fill factor (FF) in the temperature range of 20–64 °C, increasing the power conversion efficiency (PCE). This ensured that the MAPbI3 solar cell performed better in the city and the season with harsher thermal conditions (Kaduna, dry season). Thus, MAPbI3 solar cells can thrive excellently in environments where the operating temperature is below 65 °C. Overall, this study shows that the application of OHP devices in sub-Saharan climatic conditions is empirically possible with the right material modification.

Unraveling Bulk versus Surface Passivation Effects in Highly Efficient p–i–n Perovskite Solar Cells Using Thiophene‐Based Cations

Defect passivation is nowadays considered a must‐have route for high‐efficiency perovskite solar cells. However, a general rule that correlates the choice of passivating agents with performance enhancements is still missing. Herein, two different thiophene salts that are used as passivating agents are compared, namely thiophene methylammonium chloride and thiophene ethylammonium chloride (TEACl), which are used for the passivation of bulk and surface defects in triple‐cation‐based metal halide perovskites. First, it is observed that the surface passivation method leads to better device performances reaching a power conversion efficiency of 23.56%, with reduced voltage losses and increased fill factor when compared with the reference. Second, it is demonstrated that the chemical structure of the cation dictates its capability either in passivating bulk defects effectively or to form a superficial two‐dimensional/three‐dimensional heterostructure, which happens only for the TEACl case. The chemical composition and the cation dimension are responsible for device performance enhancement as observed by a joint spectroscopic and density functional theory simulations study, providing rational guidelines for further smart device design.

Influence of Mg concentration in Zn1-xMgxO buffer layers for enhanced Cu2(Sn,Ge)S3 solar cells performance

This study is focused on the influence of band alignment at the buffer/absorber interface of Cu2(Sn,Ge)S3 (CTGS) thin film solar cells fabricated on soda-lime glass substrates with an Al/Ni/Zn0.92Mg0.08O:Al/Zn1-xMgxO − 2nd buffer/CdS − 1st buffer/CTGS/Mo/glass structure. Here, Zn1-xMgxO 2nd buffers are used to minimize the energy losses and prevent direct contact between the Zn0.92Mg0.08O:Al and CTGS absorber. The study found that the conduction band offset between Zn1-xMgxO and CTGS changed from −0.68 eV (i.e., cliff-like, negative band offset) to +0.60 eV (i.e., spike-like, positive band offset) as the Mg content x increased in Zn1-xMgxO from 0 (i.e., pure ZnO) to 0.52. Optimization of the conduction band offset via tuning the Mg content in Zn1-xMgxO 2nd buffer reduced carrier recombination in the CTGS devices, improving band bending and enhancing the power conversion efficiency up to 3.1%. This was primarily attributed to an increase in short-circuit current density and fill factor.

Impact of Band‐gap Gradient in Semi‐Transparent and Bifacial Ultra‐Thin Cu(In,Ga)Se2 Solar Cells

AbstractUltra‐thin Cu(In,Ga)Se2 (CIGSe) solar cells on transparent conductive oxide back contact reduce the material consumption of rare indium and gallium and simultaneously exhibit great potential for semi‐transparent bifacial application. For highly efficient CIGSe solar cells, a steep back Ga grading and Na treatment are expected. However, Na will promote the formation of highly resistive GaOx at the rear interface owing to Ga accumulation. In this work, the three‐stage co‐evaporation process is renewed and the effect of the deposition sequence in the first stage on the Ga distribution as well as the cross‐correlated influence of Na is explored. In particular, the standard deposition sequence of Ga+In is altered to start with In. When a thin In layer is pre‐deposited on the back contact, the fill factor and efficiency increase. The deposition of In+Ga+In in the first stage of CIGSe growth leads to efficiencies 28% (on average) higher than for the standard deposition sequence of Ga+In. Additionally, 2.74% efficiency is reached under rear and 9.32% under simultaneous front and rear illumination. Therefore, adapting the deposition sequence in the first stage of CIGSe growth is identified as a key to improving the device performance on transparent back contact.

Dual interface strategies enable efficient wide bandgap perovskite solar cells

High performance wide bandgap perovskite solar cells (WB-PSCs) have found widespread applications in tandem solar cells. In WB-PSCs, achieving a high conversion efficiency relies on the effective utilization of light absorption and minimization of electronic defects. In this work, electronic defects at the surface and grain boundaries of perovskite materials have been passivated by n-butylammonium bromide (BABr) to suppress carrier non-radiative recombination. Confirmed through x-ray powder diffraction and x-ray photoelectron spectroscopy spectra, ultra-thin two-dimensional (2D) perovskite layers were successfully generated on a perovskite surface. The BABr-treated devices exhibited an increased fill factor and open circuit voltage (VOC) compared to the references. Furthermore, a nanotextured electrode with a roughness of 22.98 nm was employed to trap light. The nanotextured buried interface not only promoted light utilization but also alleviated residual stress and micro-strain in the perovskite film compared to the smooth substrate. Finally, the champion WB-PSC achieved a power conversion efficiency of 20.46% in the reverse scan. These findings pave a promising path for the development of solution-processed perovskite films on nanotextured silicon substrates to improve the performance of monolithic tandem solar cells.

Multifunctional Surface Treatment against Imperfections and Halide Segregation in Wide-Band Gap Perovskite Solar Cells.

Mixed-halide wide-band gap perovskites (WBPs) still suffer from losses due to imperfections within the absorber and the segregation of halide ions under external stimuli. Herein, we design a multifunctional passivator (MFP) by mixing bromide salt, formamidinium bromide (FABr) with a p-type self-assembled monolayer (SAM) to target the nonradiative recombination pathways. Photoluminescence measurement shows considerable suppression of nonradiative recombination rates after treatment with FABr. However, WBPs still remained susceptible to halide segregation for which the addition of 25% p-type SAM was effective to decelerate segregation. It is observed that FABr can act as a passivating agent of the donor impurities, shifting the Fermi-level (Ef) toward the mid-band gap, while p-type SAM could cause an overweight of Ef toward the valence band. Favorable band bending at the interface could prevent the funneling of carriers toward I-rich clusters. Instead, charge carriers funnel toward an integrated SAM, preventing the accumulation of polaron-induced strain on the lattice. Consequently, n-i-p structured devices with an optimal MFP treatment show an average open-circuit voltage (VOC) increase of about 20 mV and fill factor (FF) increase by 4% compared with the control samples. The unencapsulated devices retained 95% of their initial performance when stored at room temperature under 40% relative humidity for 2800 h.

Surface Reconstruction of a Perovskite Film by an Organic Salt for High-Performance Solar Cells with Improved Stability.

Organic-inorganic lead halide perovskites have undergone tremendous development due to their excellent optoelectrical properties, achieving exceptional photovoltaic performance up to over 25%. The interface engineering method has a significant role in further improving the perovskite solar cell performance to its limit. Herein, we fabricated a modified GA0.07MA0.93PbI3 perovskite film using the organic amine small molecule 3-(aminomethyl)pyridine (3AP), which increased the grain sizes and crystallinity through the modulated melting process as well as reacted with the surface component, especially the defect site of the PbI6 octahedral layer, resulting in a high-quality perovskite film. The perovskite films without (pristine) and with toluene were also fabricated to prove the significant role of the 3AP organic molecule. The 3AP-modified GA0.07MA0.93PbI3 perovskite film exhibits a long carrier lifetime and suppresses the charge recombination loss, resulting in an increased fill factor (FF) of 75.66% and a power conversion efficiency (PCE) of 17.28%, which are higher than those of pristine (FF, 66.36%; PCE, 14.06%) and toluene-treated perovskite devices (FF, 72.40%; PCE, 16.84%). More importantly, the 3AP-modified perovskite device shows remarkable environmental stability to the ambient conditions, with the PCE retaining 92% of the initial PCE for over 1000 h under ambient conditions.

Enhancing perovskite solar cells efficiency through cesium fluoride mediated surface lead iodide modulation

The presence of an excessive amount of lead iodide on the surface of perovskite solar cells (PSCs) is a significant contributing factor that adversely affects the stability of these devices when exposed to continuous light. To address this issue, we developed an effective strategy involving polishing PbI2 on a perovskite surface using CsF. In this study, we investigated the effects of CsF post-treatment on perovskite films and their photovoltaic properties. The results of the time-resolved photoluminescence and ultraviolet photoelectron spectroscopy tests reveal the significant positive impact of our passivation method based on CsF, which reduces the valence band offset between the perovskite and hole transport layers while simultaneously enhancing the carrier interface transport. PSCs treated with CsF exhibited a photoelectric conversion efficiency (PCE) of 24.25% and an increased fill factor (FF) of 81.72%, which surpassed those of the original PSCs (PCE = 22.12% and FF = 77.40%). Furthermore, after aging for over 2500 h at room temperature and in 30 ± 10% humidity, the PCE of the unpacked PSCs reduced to only 42% of the initial value. Furthermore, the devices treated with CsF maintained their impressive performance, with the PCE maintaining optimal levels at 91% of the initial efficiency.

The Stabilization of CsPbI3−xBrx Phase by Lowering Annealing Temperature for Efficient All‐Inorganic Perovskite Solar Cells

All‐inorganic perovskites are a promising solution for the fabrication of thermally stable perovskite solar cells (PSCs) with remarkable performances. However, a high annealing temperature is required for the stabilization of the photoactive phase of CsPbI3, which represents a limiting factor for their potential scaling‐up and manufacturing at industrial scale. This work demonstrates a new process for the stabilization of CsPbI3−xBrx perovskite at lower annealing temperature of 180°, based on a rational halogen substitution enabled by the introduction of dimethylammonium (DMA) additives. Bromide inclusion favors indeed the conversion from the intermediate phases to CsPbI3−xBrx. Standard mesoscopic solar cells prepared with this approach achieve a power conversion efficiency (PCE) of 14.86%, with reduced voltage losses and increased fill factor compared to the reference device. Moreover, this work proves that a rational substitution of the halide in the DMA salt is also beneficial for the devices annealed at higher temperature, achieving an encouraging PCE of 16.23%. By reducing the processing temperature, this new method widens the range of applications of all‐inorganic PSCs toward temperature‐sensitive materials and industrial applications.

Zinc-bis-8-hydroxyquinoline doped by biochar extracted from red sea algae Chlorophyta as a novel photoactive layer in heterojunction solar cells

Recently, scientists have shown interest in utilizing biochar made from natural sources to enhance various photovoltaic technologies. In this study, Zinc-Bis-8-hydroxyquinoline (Zn-Hq2) was mixed with 10 % biochar obtained from red sea microalgae (Chlorophyta) using a microwave combustion process. This mixture was then used as a novel photoactive layer in a solar cell. The structural properties of Zn-Hq2@BC were analyzed by XRD, FTIR, HRTEM, and SEM. The analysis showed that Zn-Hq2@BC had evenly distributed nano-rods within the BC nanopores network, with widths ranging from 26.94 to 30.90 nm and lengths ranging from 136.43 to 192.38 nm. When measuring dark current density-voltage, it was found that Zn-Hq2@BC/n-Si showed better-rectifying characteristics compared to pristine Zn-Hq2/n-Si, with a higher rectification ratio. The results also showed that the current density and voltage at the maximum power point increased to 5.63 mA/cm2 and 0.45 V, respectively, due to the activation of the biochar. When exposed to light, the addition of approximately 10 % biochar resulted in a 15 % increase in fill factor and a 92 % increase in power conversion efficiency. This is because biochar helps introduce extra charge carriers into the material, thus improving charge transport and reducing recombination losses. These findings reveal the positive effects of microalgae-derived biochar and indicate potential applications of Zn-Hq2 in solar cells.

Dye-sensitized solar cells with aluminum-doped zinc oxide nanoparticles-loaded electrolyte: A breakthrough solution for recombination and hysteresis suppression

Dye-sensitized solar cells (DSCs) suffer from reduced power conversion efficiency due to electron recombination with triiodide (I3−) ions at the photoanode/electrolyte interface. Organic additives are conventionally used in electrolyte to reduce recombination and improve the efficiency of the device. These additives react covalently with iodine (I2) in the electrolyte, leading to a reduction in the concentration of I3− ions. Other inorganic oxides, such as silica (SiO2), titania (TiO2), and magnesia (MgO), have been shown to improve the efficiency of the solar cell. These oxides can adsorb heavy ions to some extent. In this study, we investigated aluminum-doped zinc oxide nanoparticles (AZO NPs) as an inorganic additive with ionic adsorption properties towards I− and I3− anions in the electrolyte. We confirmed the ionic adsorption of AZO NPs through zeta potential and electrochemical impedance measurements. We observed a significant decrease in recombination between photogenerated electrons and electrolyte ions after adding AZO NPs, which resulted in an increase in open circuit voltage (VOC) and fill factor (FF) values. Furthermore, the incorporation of AZO NPs reduced the compelled hysteresis caused by the mismatch in current density-voltage curves for the forward and reverse scan direction. Mott-Schottky analysis confirmed the increase in VOC due to the negative shift in the Fermi level of the TiO2 photoanode. Additionally, open circuit voltage decay measurements indicated a longer electron lifetime at the TiO2/electrolyte interface in AZO NPs loaded electrolyte. Our findings suggest that AZO NPs have potential as an effective inorganic additive for improving the performance of DSCs.

Self‐Assembled Monolayer Ti3C2TxMXene as Electron Selective Heterocontact for Crystalline Silicon Solar Cells

Carrier‐selective contact is an essential strategy to improve the power conversion efficiency (PCE) of crystalline silicon (c‐Si) solar cells by enhancing carrier transport and reducing recombination. Many two‐dimensional transition metal carbides/nitrides (MXene) possess excellent electrical conductivity and tunable work function, enabling them as potential carrier‐selective contact materials for c‐Si solar cells. Herein, low work function (3.71 eV) monolayer Ti3C2Txthin films are fabricated with an ordered arrangement of nanosheets by interfacial self‐assembly method, and the Ti3C2Tx/n‐type c‐Si heterostructure achieves extremely low contact resistivity (22.64 mΩ cm2). Dopant‐free heterojunction crystalline silicon solar cell with self‐assembled monolayer Ti3C2Txelectron‐selective contact is reported for the first time, showing the highest PCE of 16.46% among MXene monolayer‐based c‐Si solar cells, which is mainly attributed to the greatly increased fill factor and open circuit voltage by the accession of self‐assembled monolayer Ti3C2Txas electron transport layer. This work opens up the possibility of applying MXene as electron transport material for photovoltaic devices.

Impact of B2H6 plasma treatment on contact resistivity in silicon heterojunction solar cells

We investigated the effect of the B2H6 plasma treatment on p-type hydrogenated amorphous silicon (p-a-Si:H) surfaces for high-performance silicon heterojunction (SHJ) solar cells. Secondary ion mass spectroscopy measurements revealed that the boron concentration at the p-a-Si:H surface is increased by employing the B2H6 plasma treatment. Furthermore, specific contact resistance is decreased by about one-third after the B2H6 plasma treatment. No degradation of passivation performance is induced by the B2H6 plasma treatment. The power conversion efficiency of the SHJ solar cells with the B2H6 plasma treatment is improved by the increase in fill factor (FF) due to decreased series resistance and increased shunt resistance. From numerical simulations, the upward band bending is enhanced at the heterointerface between transparent conductive oxide (TCO) and p-a-Si:H by the B2H6 plasma treatment, which is responsible for the improved FF owing to facilitated tunneling holes from c-Si to p-a-Si:H layers and the TCO/p-a-Si:H heterointerface.

Photon up-conversion in Er3+ ion-doped ZnO-Al2O3-BaO-B2O3 glass for enhancing the performance of dye-sensitized solar cells

One of the main limitations in the development of dye-sensitized solar cell (DSSC) is contributed by the optical losses that occur within the absorber layer due to spectral mismatch. DSSC typically only absorbs solar light within the visible region (i.e. up to 800 nm), while the photon energy in the infrared region remain unutilized. Here we report the integration of Er3+ ion-doped glass as up-conversion (UC) element in DSSC and study their effect on the photovoltaic performances. Several characterizations were conducted including physical, structural, optical, luminescence, and radiative properties on the glass sample, while current-voltage and incident photon-to-current conversion efficiency characterization were conducted to analyze the electrical properties of DSSC. The UC luminescence spectra of the glass sample under 800 nm excitation showed green light emissions that were located between 531 and 553 nm. The UC luminescence band of glass sample was confirmed suitable with the absorption band of Z907 dye. After placing the UC glass below the DSSC’s counter electrode side, the power conversion efficiency of DSSC were mostly positively affected by the presence of UC glass, where the highest improvement of around 7.21 % was obtained for DSSC coupled with 2.0 mol% of Er3+ ion-doped glass. The enhancement was primarily attributed to the improved light harvesting due to the UC mechanism within the device as indicated by the increase in external quantum efficiency and fill factor. Our contribution provides a simple yet versatile approach in improving DSSC performance via the application of a free standing Er3+ ion-doped up-conversion glass.

Unveiling the Selenization Reaction Mechanisms in Ambient Air‐Processed Highly Efficient Kesterite Solar Cells

AbstractThe selenization annealing process is vital for highly efficient kesterite solar cells. Generally, SnS is added during the selenization process, but excessive S and related defects are introduced. Meanwhile, the path of supplementing Sn has never been elucidated. Herein, in order to solve the above problems, a combination of strategies involving SnS and Sn or SnSe or SnSe2 is put forward. And the composition of the vapor inhibiting Sn loss (gaseous SnSe3) and the pathway through which SnSe3 facilitates the formation of Cu2ZnSn(SxSe1‐x)4 (CZTSSe) are clarified. When SnSe2 is added to SnS in the selenization process, grain fusion is effectively promoted. The high crystalline quality kesterite absorber makes the band bending at the GBs optimal and the interface recombination be effectively suppressed. Moreover, cation disorder is remarkably reduced. Therefore, the open‐circuit voltage (Voc) is significantly elevated from 508 to 546 mV with increased fill factor (FF) and short‐circuit current density (Jsc). A state‐of‐the‐art ambient air‐processed kesterite device with 12.89% efficiency is achieved, and the unveiled reaction mechanisms have guiding significance for further optimizing selenization atmosphere and elevating the efficiency of CZTSSe solar cells.