Qingwen Tian

Solution-deposited pure selenide CIGSe solar cells from elemental Cu, In, Ga, and Se

A novel, robust and low-toxicity solution route to deposit CIGSe thin films for solar cell applications is proposed. The solvent mixture of 1,2-ethanedithiol and 1,2-ethylenediamine is employed for the first time to simultaneously dissolve elemental Cu, In, Ga, and Se, forming the CIGSe precursor solution. With this solution-processed CIGSe thin film solar cell, a power conversion efficiency of 9.5% has been achieved.

p-type Li, Cu-codoped NiOx hole-transporting layer for efficient planar perovskite solar cells

p-type inorganic hole transport materials of Li, Cu-codoped NiOx films were deposited using a simple solution-based process. The as-prepared films were used as hole selective contacts for lead halide perovskite solar cell. An enhanced power conversion efficiency of 14.53% has been achieved due to the improved electrical conductivity and optical transmittance of the Li, Cu-codoped NiOx electrode interlayer.

Engineering of interface band bending and defects elimination via a Ag-graded active layer for efficient (Cu,Ag)2ZnSn(S,Se)4 solar cells

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.

ZnO nanotubes supported molecularly imprinted polymers arrays as sensing materials for electrochemical detection of dopamine

In this study, ZnO nanotubes (ZNTs) were prepared onto fluorine-doped tin oxide (FTO) glass and used as supports for MIPs arrays fabrication. Due to the imprinted cavities are always located at both inner and outer surface of ZNTs, these ZNTs supported MIPs arrays have good accessibility towards template and can be used as sensing materials for chemical sensors with high sensitivity, excellent selectivity and fast response. Using K3[Fe(CN)6] as electron probe, the fabricated electrochemical sensor shows two linear dynamic ranges (0.02-5μM and 10-800μM) towards dopamine. This proposed electrochemical sensor has been applied for dopamine determination with satisfied recoveries and precision. More complex human urine samples also confirmed that the proposed method has good accuracy for dopamine determination in real biological samples. These results suggest potential applicability of the proposed method and sensor in important molecule analysis.

Elemental Precursor Solution Processed (Cu1–xAgx)2ZnSn(S,Se)4 Photovoltaic Devices with over 10% Efficiency

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.

Eliminating fine-grained layers in Cu(In,Ga)(S,Se)2 thin films for solution-processed high efficiency solar cells

A non-hydrazine solution process has been considered as a promising way for the deposition of Cu(In,Ga)(S,Se)2(CIGSSe) thin films. However, from our previous work, the presence of a fine-grained layer in the absorber layer was shown to be an obstacle to further improve the solar cell efficiency. Here, an improved fabrication route is proposed to solve this problem. A mixture of Cu2S, In2Se3, Ga and Se was simultaneously dissolved in 1,2-ethanedithiol and 1,2-ethylenediamine, forming a homogeneous precursor solution to deposit CIGSSe nanocrystal films. By optimizing the selenization method by using rapid thermal processing (RTP) combined with an improved graphite box, large grains throughout the whole absorber layer were successfully obtained. Based on such a high-quality CIGSSe absorber layer, an encouraging power conversion efficiency of 11.8% has been achieved with a Jsc of 28.25 mA cm−2, a Voc of 596 mV and a FF of 69.79% and without an antireflection coating.

Cu2ZnSnS4–CdS heterostructured nanocrystals for enhanced photocatalytic hydrogen production

The CZTS–CdS heterostructured nanocrystals were designed and synthesized via a wet chemistry approach for the first time. The p–n heterojunction between CZTS core and CdS layer facilitates a effective charge separation and a rapid charge transfer. As expected, these CZTS–CdS-heterostructured nanocrystals show enhanced photocatalytic activities for hydrogen evolution when compared with CZTS and CdS.

Regulating the starting location of front-gradient enabled highly efficient Cu(In,Ga)Se2 solar cells via a facile thiol–amine solution approach

The introduction of a double-gallium (Ga) gradient plays a key role in pushing the performance of Cu(In,Ga)Se2 (CIGSe) solar cells to a more competitive level. In particular, the location of the front-gradient starting position strongly affects the barrier of the electron transport path, and this is not based on either significantly reducing the electron collection or decreasing the fill factor. Here we present and implement a double-Ga gradient design for CIGSe absorber layers using a diamine–dithiol solution approach. By regulating the front-gradient starting location, three CIGSe absorber layers with different Ga gradients were successfully constructed; these materials maximize solar spectrum absorption and improve the charge collection efficiency. Moreover, this facile solution-process approach does not require expensive vacuum equipment and can be applied to roll-to-roll printing technology. By combining optimal front-gradients with the back gradient, the short-circuit current has been increased by 17% and a maximum improvement in CIGSe efficiency to 13.12% achieved through adjusting the front-gradient to an optimum location.