Solvent Engineering for Controlled Crystallization and Growth of All-Inorganic Pb-Free Rudorffite Absorbers of Perovskite Solar Cells.

Solution-processed Ag-Bi-I rudorffites with direct band gaps of <2 eV show promise for highly efficient and cost-effective Pb-free solar cells. However, relatively fast crystallization rates of Bi-based films and limited solubility of BiI3 in many solvents result in poor film morphologies, inhibiting their device performance. Here, we conduct a solvent-engineering method to adjust the dynamics of nucleation and growth during film formation. We fabricate Ag2BiI5, AgBiI4, and AgBi2I7 absorber layers using a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and find that a volume percentage of 50% DMSO causes highly uniform and dense perovskite films via a BiI3-DMSO-AgI intermediate phase formation, leading to solar cells with an improved power conversion efficiency of 0.62% for the Ag2BiI5 absorber. These results provide valuable insights into the optimization of the solution processing technique to realize low-toxicity and efficient perovskite solar cells.

Incorporating carbon nanotubes in sol-gel synthesized indium tin oxide transparent conductive films.

Carbon nanotubes (CNTs) are incorporated in indium tin oxide (ITO) films through a sol-gel dip coating method. CNT incorporation has no effect on lattice parameter and preferential orientation of the ITO matrix. Raman spectrum confirms the presence of CNTs in the ITO matrix. The surface roughness is decreased by CNT addition. Moreover, the optical transmittance of the ITO-CNT films is more than that of ITO films in the IR region. The higher transmittance region of the ITO-CNT films compared to that of ITO films is extended to the visible region with increasing thickness of the films. In terms of electrical resistance, the ITO film shows slightly lower sheet resistance compared to the ITO-CNT film. However, the sheet resistance of the ITO-CNT film is further reduced by thickness and reaches the minimum amount in the 15-layer deposited sample, which is lower than that of ITO samples. It seems that CNT incorporation in the ITO matrix can dramatically reduce microcrack formation, especially in higher thicknesses. Furthermore, the sensitivity of ITO films to thermal cycling is dramatically enhanced with CNT addition. In addition, the figure of merit of ITO films is strongly improved in the vis-NIR region with CNT incorporation.

Incorporation of carbon nanotubes in a hierarchical porous photoanode of tandem quantum dot sensitized solar cells.

The incorporation of multi-walled carbon nanotubes (MWCNT) in quantum dot (QD) sensitized solar cells (QDSC) based on CdSe QDs and quantum rods (QRs) is investigated. The composite hierarchical porous photoanode of titania/CNT is synthesized by sol-gel induced phase separation and QDs/QRs are prepared by the modified solvothermal method. The QDs and QRs form a tandem structure on the hierarchical porous photoanode after deposition by the electrophoretic method. Incorporation of MWCNT in the QDSC photoanode in optimum content (0.32 wt%) causes appreciable enhancement in cells efficiency (about 41% increase). This improvement in efficiency mainly emerges from the beneficial role of MWCNTs in charge injection and collection. The MWCNTs result in longer electron lifetime and higher electron diffusion length, which is confirmed by electrochemical impedance spectroscopy.