A novel organic small molecule bis-triphenylamine with spiro(fluorene-9,9'-xanthene) as the conjugated system, named BTPA-4, is successfully synthesized and employed as the hole-selective layer (HSL) in colloidal quantum dots solar cells (CQDSCs). The introduction of BTPA-4 layer can significantly prolong effective carrier lifetime (τ), increase charge recombination resistance (R), and thus diminish the interfacial charge recombination at the PbS-QDs/Au electrode interface. The effect of BTPA-4 as HSL in the device performance is especially significant for the open-circuit voltage (V) and power conversion efficiency (PCE), with a ∼ 10% and 15% enhancement respectively, comparing with those of device without the HSL. Furthermore, the PbS CQDSCs with BTPA-4 possessed a noticeably stable property for over 100 days of storage under ambient atmosphere.

Lead selenide (PbSe) colloidal quantum dots (CQDs) are considered to be a strong candidate for high-efficiency colloidal quantum dot solar cells (CQDSCs) due to its efficient multiple exciton generation. However, currently, even the best PbSe CQDSCs can only display open-circuit voltage ( V) about 0.530 V. Here, we introduce a solution-phase ligand exchange method to prepare PbI-capped PbSe (PbSe-PbI) CQD inks, and for the first time, the absorber layer of PbSe CQDSCs was deposited in one step by using this PbSe-PbI CQD inks. One-step-deposited PbSe CQDs absorber layer exhibits fast charge transfer rate, reduced energy funneling, and low trap assisted recombination. The champion large-area (active area is 0.35 cm) PbSe CQDSCs fabricated with one-step PbSe CQDs achieve a power conversion efficiency (PCE) of 6.0% and a V of 0.616 V, which is the highest V among PbSe CQDSCs reported to date.

Using spatial energy-level gradient engineering with quantum dots (QDs) of different sizes to increase the generated carrier collection at the junction of a QD heterojunction solar cell (QDHSC) is a hopeful route for improving the energy-conversion efficiency. However, the results of current related research have shown that a variable band-gap structure in a QDHSC will create an appreciable increase, not in the illumination current density, but rather in the fill factor. In addition, there are a lack of studies on the mechanism of the effect of these graded structures on the photovoltaic performance of QDHSCs. This study presents the development of air atmosphere solution-processed TiO/PbS QDs/Au QDHSCs by engineering the energy-level alignment (ELA) of the active layer via the use of a sorted order of differently sized QD layers (four QD sizes). In comparison to the ungraded device (without the ELA), the optimized graded architecture (containing the ELA) solar cells exhibited a great increase (21.4%) in short-circuit current density ( J). As a result, a J value greater than 30 mA/cm has been realized in planar, thinner absorption layer (∼300 nm) PbS QDHSCs, and the open-circuit voltage ( V) and power-conversion efficiency (PCE) were also improved. Through characterization by the light intensity dependences of the J and V and transient photovoltage decay, we find that (i) the ELA structure, serving as an electron-blocking layer, reduces the interfacial recombination at the PbS/anode interface, and (ii) the ELA structure can drive more carriers toward the desirable collection electrode, and the additional carriers can fill the trap states, reducing the trap-assisted recombination in the PbS QDHSCs. This work has clearly elucidated the mechanism of the recombination suppression in the graded QDHSCs and demonstrated the effects of ELA structure on the improvement of J. The charge recombination mechanisms characterized in this work would be able to shed light on further improvements of QDHSCs, which could even benefit other types of solar cells.

The performance of perovskite solar cells (PSCs) is known to be extremely sensitive to humidity in the preparation environment. However, the main mechanism by which the moisture influences the quality of the perovskite film and the device performance is not yet fully understood. Herein, a new strategy is established to obtain inverted PSCs with a remarkabll high VOC by including a high‐humidity treatment and sufficient DMSO‐atmosphere annealing in the preparation process. It is found that the lattice distortion on the surface of perovskite grains caused by the high‐humidity treatment plays a key role in the self‐passivation of perovskite. Inverted (p‐i‐n) PSCs based on the self‐passivated perovskite films show effective suppression of nonradiative recombination, which increase the device VOC to 1.17 V and achieve the highest efficiency of 21.38%. It is expected that the findings of this work shed more light on the currently proposed mechanism governing the action of moisture on the performance of the PSCs.

Conventional methods for measuring contact angle are usually applied on smooth surfaces. Methods concerning contact angle determinations performed directly on pore surfaces of porous media have rarely been reported. This work approaches the pore-scale measurement of local contact angle in a CO 2-brine-glass beads system, using micro-focused X-ray computed tomography (micro-CT). Both drainage and imbibition experiments with 0.1 ml/min injection rate were conducted at 40°C and 8 MPa. The effectiveness of this pore-scale approach is confirmed by comparing the results with the results gathered from traditional sessile drop methodology. Observations indicate that the contact angle hysteresis phenomenon was not so obvious for intermediate-wet glass beads in the employed experimental setting. In real reservoir circumstances, the roughness and capillary variation caused significant deviations in contact angle distribution for both drainage and imbibition, even in rock cores consisting of a single-phase material.