Search

A high-efficiency CZTSSe solar cell was achieved through the modification of the back interfacial contact with a MoO3 layer synthesized in situ using Na2S aqueous solution.

The environmentally friendly Cu2ZnSn(S,Se)4 (CZTSSe) compounds are promising direct bandgap materials for application in thin film solar cells, but the spontaneous surface defects disordering would lead to large open-circuit voltage deficit (Voc,deficit) and significantly limit kesterite photovoltaics performance, primarily arising from the generated more recombination centers and insufficient p to n conversion at p-n junction. Herein, we establish a surface defects ordering structure in CZTSSe system via local substitution of Cu by Ag to suppress disordered CuZn defects and generate benign n-type ZnAg donors. Taking advantage of the decreased annealing temperature of AgF post deposition treatment (PDT), the high concentration of Ag incorporated into surface absorber facilitates the formation of surface ordered defect environment similar to that of efficient CIGS PV. The manipulation of highly doped surface structure could effectively reduce recombination centers, increase depletion region width and enlarge the band bending near p-n junction. As a result, the AgF-PDT device finally achieves maximum efficiency of 12.34% with enhanced Voc of 0.496 V. These results offer a new solution route in surface defects and energy-level engineering, and open the way to build up high quality p-n junction for future development of kesterite technology.

Cs treatment in a CZTSSe system could enhance device performance by affecting defect characteristics and carrier–transport properties.

A solution-processed ZnO:Li NP window layer is demonstrated to enhance charge collection and minimize interface recombination in kesterite solar cells.

The development of kesterite photovoltaic solar cells has been hindered by large open-circuit voltage (Voc) deficit. Recently, SnZn deep point defect and associative defect cluster have been recognized as the main culprit for the Voc losses. Therefore, manipulating the deep-level donor of SnZn antisite defects is crucial for breaking through the bottleneck of present Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic technology. In this study, the SnZn deep traps in CZTSSe absorber layer are suppressed by incorporation of Ge. The energy levels and concentration of SnZn defects measured by deep-level transient spectroscopy (DLTS) decrease significantly. In addition, the grain growth of CZTSSe films is also promoted due to Ge implantation, yielding the high quality absorber layer. Consequently, the efficiency of CZTSSe solar cells increases from 9.15% to 11.48%, largely attributed to the 41 mV Voc increment.

Black phosphorus (BP) is one of the most promising visible-near-infrared light-driven photocatalysts with favorite photoelectric properties and unique tunable direct band gap. Nevertheless, the further development of BP is hindered by the fast carrier recombination rate and high Gibbs free energy. Herein, an innovative strategy is developed for the controllable construction of Zn-P bonds induced zinc ferrite/black phosphorus (ZnFe2O4-BP) three dimensions (3D) microcavity structure. The Zn-P bonds serve as an efficient channel to optimize the carrier transport and Gibbs free energy of BP simultaneously. Besides, the unique 3D core-shell microcavity structure maintains the multiple reflections of sunlight inside the catalysts, which greatly improves the sunlight utilization upon photocatalysis. An optimized photocatalytic hydrogen production rate of 560 µmol h-1g-1 under near-infrared light (>820 nm) is achieved. A possible photocatalytic mechanism is proposed based on a series of experimental characterizations and theoretical calculations, this work provides a new sight to design high-quantity BP-based full-spectrum photocatalysts for solar energy conversion.

Solution processing of Cu(In,Ga)Se

The introduction of alkali metal (AM) post-deposition treatment (PDT) has led to the consecutive breakthrough of world record efficiencies for Cu(In,Ga)Se2 photovoltaics. However, for the derivative Cu2SnZn(S,Se)4 (CZTSSe) solar cells, the corresponding verdict seems partially unjustified due to the difference in defect chemical environment and phase structure, and the most effective incorporation means of AMs is still a mystery. In this work, for the first time, we developed a dual AM synergistic incorporation strategy combining light and heavy AMs by post-depositing CsF after NaF-PDT to improve the efficiency of CZTSSe solar cells. The relevant microscopic-electrical advantages with regard to the different roles of NaF and CsF PDT are discussed in more detail. It was found that the Na atoms are randomly dispersed both in the grain interior (GI) and grain boundaries (GBs), significantly increasing the acceptor concentration and passivating the deep level defects to enhance the Voc. In contrast, the Cs atoms are mainly segregated at the GBs, primarily increasing the potential of the GBs and improving the FF. The prominent electric benefits of Cs at the GBs and Na in the GI finally increase the device efficiency from 10.12% to 12.16%. Our findings solve the difficulty in obtaining the available Voc and FF for future high efficiency research and should serve as a basis for the in-depth understanding of AM-PDT in kesterite photovoltaics.

Interfacial properties play a significant role in the photovoltaic performance of kesterite solar cells. Different from its predecessor of Cu(In,Ga)S(e)2, the interface between Cu2ZnSnS(e)4 (CZTSSe...

Although silver (Ag) substitution offers several benefits in eliminating bulk defects and facilitating interface type inversion for Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic (PV) technology, its further development is still hindered by the fairly low electrical conductivity due to the significant decrease of acceptors amount. In this work, a versatile Li–Ag co-doping strategy is demonstrated to mitigate the poor electrical conductivity arising from Ag through direct incorporating Li via postdeposition treatment (PDT) on top of the Ag-substituted CZTSSe absorber. Depth characterizations demonstrate that Li incorporation increases p-type carrier concentration, improves the carrier collection within the bulk, reduces the defects energy level as well as inverts the electric field polarity at grain boundaries (GBs) for Ag-substituted CZTSSe system. Benefiting from this lithium-assisted complex engineering of electrical performance both in grain interior (GI) and GBs, the power conversion efficiency (PCE) is finally increased from 9.21% to 10.29%. This systematic study represents an effective way to overcome the challenges encountered in Ag substitution, and these findings support a new aspect that the synergistic effects of double cation dopant will further pave the way for the development of high efficiency kesterite PV technology.

g-C3N4 has great application prospect in the field of photocatalytic nitrogen fixation owing to the advantages of abundant raw materials, low toxicity, low consumption, high efficiency and stability. However, the low surface-active site and high carrier recombination rate limit their nitrogen fixation activities. Defect regulation is one of the effective methods to improve photocatalytic nitrogen fixation activity. In this paper, g-C3N4 nanosheets are successfully modified by ZnS containing zinc vacancy, which enhanced the carrier transport capacity and active site of g-C3N4 for photocatalytic nitrogen fixation. Thus, without any sacrificial agent, an optimized nitrogen fixation activity of 2.1 µmol·h−1 (105 µmol·h−1·g−1) is achieved with the irradiation of visible light, which presents obvious advantages among the latest reported g-C3N4 related photocatalysts. The morphology, structure and photocatalytic carrier dynamics of the photocatalyst are studied by a series of experimental characterizations.

Material crystallinity is the overriding factor in the determination of the photoelectric properties of absorber materials and the overall performance of the photovoltaic device. Nevertheless, in t...

A major obstacle hindering further development of kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells is the inherent recombination losses that occur both via bulk defects and charge extraction interfaces. Herein, we propose a generic Ag, Ge dual-gradient absorber architecture, involving a downshift of absorber VBM at the front contact and an upshift of absorber CBM at the back contact, to improve device performance. We experimentally show that the substitution of Cu by Ag allows for larger band bending at the p–n junction, and the substitution of Sn by Ge imposes an additional drift field within the quasi-neutral region. Additionally, the Ag and Ge ions diffusing into the bulk absorber passivate the deleterious CuZn and CuSn deep-level defects. In turn, accelerated charge extraction, transport and minimized recombination loss offered surprising gains in Voc and Jsc, and the dual-gradient device achieved a maximum efficiency of 12.26% with an improved Voc,deficit of 553 mV. This Ag, Ge graded-substitution approach offers an alternative absorber architecture to improve the Voc,deficit in future high-efficiency kesterite PV cells.

Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have been receiving considerable attention in recent years, owing to their low cost and toxicity as well as a high abundance of their constituent elements. Solution-based (mainly precursor solution) methods have been widely used in the fabrication of CZTSSe-based thin film solar cells. Though most record solar cells since 2009 have been achieved using solution-based methods, carbonaceous residues are always formed during post deposition treatment (PDT). These carbonaceous residues are detrimental to grain growth of CZTSSe to form large grains. The presence of unwanted small grain layers will increase the series resistance and reduce the fill factor of the solar cell, thus consequently decreasing the efficiency of CZTSSe solar cells. Herein, we propose “green” supercritical carbon dioxide (SCCO2) treatment to overcome the challenge of carbonaceous residues. FT-IR, SEM, XRD and Raman characterization studies were used to confirm the reduction of carbonaceous residues in CZTSSe films. The solar cell fabricated from a selenized CZTSSe precursor film with SCCO2 treatment under optimal conditions showed the best conversion efficiency of 11.23% (VOC = 0.456 V, JSC = 36.6 mA cm−2, FF = 67.1%). To the best of our knowledge, this is the first report on boosting the efficiency of solution-based CZTSSe solar cells by using SCCO2 treatment. In addition, this unique SCCO2 treatment may also bring forth new ideas for other solution-based optoelectronic devices.

Black phosphorus (BP) is one of the most promising visible-near-infrared light-driven photocatalysts with favorite photoelectric properties and unique tunable direct band gap. Nevertheless, the further development of BP is hindered by the fast carrier recombination rate and high Gibbs free energy. Herein, an innovative strategy is developed for the controllable construction of Zn-P bonds induced zinc ferrite/black phosphorus (ZnFe

Although the traditional Cu-poor architecture addresses many limitations for Cu2ZnSn(S,Se)4 solar cells, its further development still encounters a bottleneck in terms of efficiency, primarily arising from the inferior charge transport within the quasineutral region and enlarged recombination at back contact. On the contrary, the electrical benign kesterite compound with higher Cu content may compensate for these shortages, but it will degrade device performance more pronouncedly at front contact because of the Fermi level pinning and more electric shunts. Based on the electric disparities on their independent side, in this work, we propose a new status of Cu component by exploring a large grain/fine grain/large grain trilayer architecture with higher Cu content near back contact and lower Cu content near front contact. The benefits of this bottom Cu-higher strategy are that it imposes a concentration gradient to drive carrier diffusion toward front contact and decreases the valence band edge offset in the rear of the device to aid in hole extraction. Also, it maintains the Cu-poor architecture at the near surface to facilitate hole quasi-Fermi level splitting. In return, the local Cu component engineering-mediated electric advances contribute to the highest efficiency of 12.54% for kesterite solar cells using amine-thiol solution systems so far.

Se-rich selenization offers remarkable benefits for grain growth of Cu2ZnSn(S,Se)4 (CZTSSe) absorber layers, which is critical for solar cells fabrication. However, low-activity selenium often forms Se-clusters and trapped in CZTSSe absorber layers. These trapped Se-clusters increase carrier recombination in CZTSSe absorber layers, thus decreasing efficiency of CZTSSe solar cells. Herein, supercritical carbon dioxide (SCCO2) treatment was demonstrated to regulate selenium composition of CZTSSe absorber layers for solar cells efficiency improvement. Compared with untreated CZTSSe absorber layers, selenium composition of CZTSSe absorber layers were significantly reduced by SCCO2 treatment. The open circuit voltage (VOC) and fill factor (FF) of CZTSSe solar cells improved pronouncedly due to carrier recombination reduction and carrier transport enhancement. As a consequence, the power conversion efficiency (PCE) was increased from 9.26 % (ref device) to 11.43 % (SCCO2 device). This unique SCCO2 treatment may offer new ideas for other selenization-based optoelectronic devices performance improvement.

The partial substitution of Cu+ with Ag+ into the host lattice of Cu2ZnSn(S,Se)4 thin films can reduce the open-circuit voltage deficit (Voc,deficit) of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. In this paper, elemental Cu, Ag, Zn, Sn, S, and Se powders were dissolved in solvent mixture of 1,2-ethanedithiol (edtH2) and 1,2-ethylenediamine (en) and used for the formation of (Cu1–xAgx)2ZnSn(S,Se)4 (CAZTSSe) thin films with different Ag/(Ag + Cu) ratios. The key feature of this approach is that the impurity atoms can be absolutely excluded. Further results indicate that the variations of grain size, band gap, and depletion width of the CAZTSSe layer are generally determined by Ag substitution content. Benefiting from the Voc enhancement (∼50 mV), the power conversion efficiency is successfully increased from 7.39% (x = 0) to 10.36% (x = 3%), which is the highest efficiency of Ag substituted devices so far.

Although the substitution of Cu by Ag to suppress CuZn defects offers several advantages in overcoming the large open-circuit voltage (Voc) deficit for Cu2ZnSn(S,Se)4 (CZTSSe) solar cells, an excellent performance has not been achieved to date primarily due to the Fermi level pinning at the CdS/absorber interface and large recombination at the absorber/Mo interface. Herein, we developed a composition grading strategy to achieve a V-shaped Ag-graded structure with a higher Ag content on both the back and front surfaces of the (Cu,Ag)2ZnSn(S,Se)4 (CAZTSSe) layer. The key advantages of this Ag-graded structure are as follows: the higher content towards the CdS/absorber interface can create weak n-type donor defects and retard Fermi level pinning, whereas the lower content at the interlayer maintains the conductivity and light absorption; moreover, the other higher content towards Mo back contact can effectively suppress the recombination and improve the utilization of long-wave incident light. By appropriately adjusting the Ag gradient, we demonstrated a significant increase in Voc, and an unexpected conversion efficiency of 11.2% was achieved. This is the highest efficiency achieved to date for Ag-substituted CZTSSe solar cells, and the result supports a new aspect that synthesis of a composition-graded CAZTSSe absorber has great potential for future research.

The partial substitution of Cu