Nitrogen-doped titanium dioxide (TiO 2 /N) nanoparticle thin films have been produced by a sol-gel method with hexamethylenetetramine (HMT) as the dopant source. The synthesized TiO 2 /N thin films have been sensitized with CdSe quantum dots (QDs) via a linking molecule, thioglycolic acid (TGA). Optical, morphological, structural, and photocurrent properties of the thin films with and without QD sensitization have been characterized by AFM, TEM, XPS, Raman spectroscopy, UV-visible spectroscopy, and photoelectrochemistry techniques. AFM measurements reveals that films with thicknesses of 150 and 1100 nm can be readily prepared, with an average TiO 2 particle size of 100 nm. TEM shows a uniform size distribution of CdSe QDs utilized in sensitizing the TiO 2 /N films. Doping of the TiO 2 crystal lattice by HMT was confirmed to be 0.6-0.8% by XPS. Differences in crystal phase caused by the precursors HMT, nitric acid, and poly(ethylene glycol) (PEG) are elucidated using XRD and Raman spectroscopy. The resultant crystal phase of TiO 2 /N varies but is a mixture of anatase, brookite, and rutile phases. UV-visible absorption spectra show that N doping of TiO 2 causes a red-shifted absorption into the visible region, with an onset around 600 nm. Nitrogen doping is also responsible for the enhanced photocurrent response of the TiO 2 /N nanoparticle films in the visible region relative to undoped TiO 2 films. In addition, CdSe QDs linked to TiO 2 /N nanoparticles using TGA were found to significantly increase the photocurrent and power conversion of the films compared to standard TiO 2 /N films without QD sensitization. The incident photon-to-current conversion efficiency (IPCE) is 6% at 400 nm for TiO 2 /N-TGA-CdSe solid-state solar cells and 95% for TiO 2 /N-TGA-CdSe films near 300 nm in a Na 2 S electrolyte, which is much higher than that of undoped TiO 2 with QD sensitization or TiO 2 /N without QD sensitization. The power conversion efficiency (η) was found to be 0.84% with a fill factor (FF%) of 27.7% with 1100 nm thick TiO 2 /N-TGA-CdSe thin films. The results show that combining nitrogen doping with the QD sensitization of TiO 2 thin films is an effective and promising way to enhance the photoresponse in the near-UV and visible region, which is important for potential photovoltaic (PV) and photoelectrochemical applications.

The performance of perovskite solar cell (PSC) is highly sensitive to deposition conditions, the substrate, humidity, and the efficiency of solvent extraction. However, the physical mechanism involved in the observed changes of efficiency with different deposition conditions has not been elucidated yet. In this work, PSCs were fabricated by the antisolvent deposition (AD) and recently proposed air-extraction antisolvent (AAD) process. Impedance analysis and J-V curve fitting were used to analyze the photogeneration, charge transportation, recombination, and leakage properties of PSCs. It can be elucidated that the improvement in morphology of perovskite film promoted by AAD method leads to increase in light absorption, reduction in recombination sites, and interstitial defects, thus enhancing the short-circuit current density, open-circuit voltage, and fill factor. This study will open up doors for further improvement of device and help in understanding its physical mechanism and its relation to the deposition methods.

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We report the incorporation of all-inorganic highly stable CsPbX 3 (X = I, Br) based perovskite nanoparticles (NPs) on top of a bulk CH 3 NH 3 PbI 3 perovskite thin film. This design utilizes the photogeneration ability of perovskite NPs and also improves the interfacial charge transport which happens to be a critical factor in deciding the photovoltaic performance of any solar cell device. With variation in the lead halide (PbX 2 , X = I, Br, Cl) content, the synthesized CsPbX 3 NPs shows tunable band-edge position and fluorescence characteristics. The interaction of all inorganic NPs with the bulk perovskite resulted in improved hole injection and electron blocking characteristics leading to enhanced light harvesting efficiency. The CsPbBr 3 and CsPbI 3 perovskite NPs were used for fabricating the bulk-NP structure due to their better absorption and valence band edge characteristics. The inclusion of CsPbI 3 NPs on top of the bulk perovskite showed a significant increment in the power conversion efficiency of 28%, in comparison with a reference sample without NPs, due to significant improvements in current density, open circuit voltage, and fill factor.