Absorber For Photovoltaic Applications Research Articles

Room-temperature synthesis of lead-free copper(I)-antimony(III)-based double perovskite nanocrystals

In the field of perovskite solar cells, explorations of new lead-free all-inorganic perovskite materials are of great interest to address the instability and toxicity issues of lead-based hybrid perovskites. Recently, copper-antimony-based double perovskite materials have been reported with ideal band gaps, which possess great potential as absorbers for photovoltaic applications. Here, we synthesize Cs2CuSbCl6 double perovskite nanocrystals (DPNCs) at ambient conditions by a facile and fast synthesis method, namely, a modified ligand-assisted reprecipitation method. We choose methanol as a solvent for precursor salts as it is less toxic and easily removed in contrast to widely used dimethylformamide. Our computational structure search shows that the Cs2CuSbCl6 structure containing alternating [CuCl6]5− and [SbCl6]3− octahedral units is a metastable phase that is 30 meV/atom higher in energy compared to the ground state structure with [CuCl3]2− and [SbCl6]3− polyhedra. However, this metastable Cs2CuSbCl6 double perovskite structure can be stabilized through solution-based nanocrystal synthesis. Using an anion-exchange method, Cs2CuSbBr6 DPNCs are obtained for the first time, featuring a narrow bandgap of 0.9 eV. Finally, taking advantage of the solution processability of DPNCs, smooth and dense Cs2CuSbCl6 and Cs2CuSbBr6 DPNC films are successfully fabricated.

Investigation and Mitigation of Sputter Damage on Co‐Evaporated Cu(In,Ga)Se2 Absorbers for Photovoltaic Applications

Herein, the detrimental impact of radio frequency (RF)‐sputtering on bare Cu(In,Ga)Se2 photovoltaic absorbers in view of vacuum‐deposited buffer layers is evaluated, and the possible mitigation strategies are explored. Carrier lifetimes are measured using time‐resolved photoluminescence before and after buffer deposition and exposure to the plasma environment. When directly applied on bare Cu(In,Ga)Se2 absorbers, RF‐sputtering is severely limiting the device performance, with oxygen ions emanating from the target having a stronger effect than argon ions from the process gas. The possibilities to avoid sputter damage by atomic layer deposited Zn1−xMgxO and chemical bath deposited CdS buffer layers are shown, and the ability of the latter to restore damaged surfaces is highlighted. Absorber performance is also investigated for absorbers stored in air, N2, or ultra‐high vacuum. The reduction in carrier lifetime is reflected in the reduced open‐circuit voltage of solar cells. SCAPS simulations are used to investigate possibilities to minimize the effect of sputter damage. Finally, options on how to minimize sputter damage during buffer deposition as well as on how to modify the absorber to be less sensitive are discussed.

Extrinsic Doping of Ink‐Based Cu(In,Ga)(S,Se)2‐Absorbers for Photovoltaic Applications

AbstractThe addition of cesium into Cu(In,Ga)(S,Se)2‐short CIGSSe‐absorber layers (fabricated via vacuum deposition methods), has most recently culminated in devices with record power conversion efficiencies up to 23.4%. However, research is increasingly being devoted to the development of ink deposition routes to prepare high‐quality CIGSSe thin films while requiring only a fraction of the processing costs. Such non‐vacuum deposition routes must compete with efficiencies of incumbent technologies to find adoption on a wide scale. At present, the performance of ink‐based devices still fall short of their vacuum counterparts with certified champion cell efficiencies up to 17.7%. The recent performance progression for vacuum‐processed CIGSSe exemplifies the importance of controlling the concentration of extrinsic impurities and serves as an inspiration for gains (e.g., morphological, optoelectronic) for devices with ink‐based absorber layers. This article reviews extrinsic doping concepts for CIGSSe‐type absorbers fabricated by ink‐based deposition routes (both nanoparticle dispersions and molecular inks), provides a performance comparison of select high‐efficiency ink‐based devices, and offers an outlook for future process development in general. It is suggested that the mechanisms by which dopant atoms diffuse, interact, and alter the properties of an ink‐based absorber are fundamentally different than those fabricated from vacuum‐based processes, and require further investigation.

Low-cost deposition of cupric oxide thin films for optoelectronic applications

Copper oxide is a compound that has been considered significant owing to its many advantages such as easy availability of copper in huge quantity, its non-toxic nature and the good electrical and optical properties. It is p-type with bandgap range of 1.21–1.51 eV and has potential of absorption of solar spectrum. In this work, sol–gel chemistry is explored to deposit CuO using cupric chloride dihydrate (CuCl2 · 2H2O) with 5, 10 and 15% concentration of EDTA (capping agent) using low-cost dip-coating and annealed at 400 °C. The bandgap of the CuO films was found to be in the range of 1.3–1.8 eV, which is comparable with the reported values and also suggests quantum shift in these nanostructures. These investigations suggest suitability of these layers as absorber for photovoltaic applications. SEM investigation suggests the uniform growth of layers by dip-coating techniques. Capping also appears to control the grain growth as observed by electron microscopy. Sol–gel dip-coating technique is presented in this study for deposition of flat layers.

Polymer-Passivated Inorganic Cesium Lead Halide Perovskites for High-Voltage and High-Efficiency Solar Cells

Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to its superb thermal stability. However, the large energy losses (Eloss) in the conversion from photons to electrons observed in many inorganic perovskite solar cells has become a major hindrance impairing the ultimate efficiency of these devices. Here, we report an effective and reproducible method of modifying the interface between a CsPbI2Br absorber and polythiophene hole-acceptor to minimize the Eloss. We demonstrate that polythiophene, deposited on the top of CsPbI2Br, can significantly reduce electron-hole recombination within the perovskite, which is due to the electronic passivation of surface defect states. In addition, the interfacial properties are improved by a simple annealing process, leading to significantly reduced energy disorder in polythiophene and enhanced hole-injection into the hole-acceptor. Consequently, a record power conversion efficiency (PCE) of 12.09% in inorganic perovskite solar cells is obtained, together with a high open-circuit voltage (VOC) over 1.3 V, under 100 mWcm-2 AM1.5G solar illumination. This method provides a new route to further improve the efficiency of perovskite solar cells by minimizing the Eloss.

Deposition of CuCdS2 thin film by single step solution process at low temperature as a novel absorber for photovoltaic applications

Thin film of ternary compound semiconductor, copper cadmium sulphide (CuCdS2) was deposited on glass substrate by low temperature solution process. The deposited CuCdS2 thin film was found to suitable for the fabrication of efficient thin film solar cells at low cost. Hexagonal structure of poly crystalline CuCdS2 was formed from the combination of its binary constituents CuxS and CdS. The film was continuously coated and particles were aggregated like spherical granules. The presence of elements Cu, Cd and S were confirmed by electron energy loss spectroscopy and X-ray photoelectron spectroscopy. The absorption spectrum showed that the deposited material had wide range of absorption in visible and near-IR region (300–1100nm) and band gap was estimated to be 1.42eV using Tauc’s plot. Vibration modes of CdS and CuxS binary phases were observed and shift between them revealed the existence of binding state between CdS and CuxS. Hall measurement showed p-type conducting nature of charge carriers with higher carrier concentration 3.48×1018cm−3. The mobility and resistivity were measured to be 10.63cm2/Vs and 0.17Ωcm, respectively. The analyses revealed that the deposited CuCdS2 thin film was suitable material for the fabrication of thin film solar cells at low cost.