comprised of a conjugated polymer as the electron donor and a fullerene derivative as the electron acceptor. [2,3] Conventional fullerene acceptors like [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) may be unfavorable for practical application, due to the inefficient absorption in visible and near-infrared (IR) regions, fixed molecular structure, complex purification process, and other complications well-documented in the literature. [4][5][6][7][8] In addition, the morphology of polymer-fullerene blends is very sensitive to thermal annealing, solvent additive, film thickness, and especially D:A ratio, resulting in significantly different device performance. [9][10][11] Recently, people have shown that the integration of either polymeric or molecular acceptor into photovoltaic devices would be advantageous. The chemical structures of nonfullerene acceptor can be easily adjusted to tune their energy levels, and the conjugated molecule or polymer acceptor demonstrates enhanced absorption at long wavelengths relative to fullerenes. [12] Thus nonfullerene photovoltaics can have improved harvest of solar radiation, enhanced thermal and mechanical stability, and reduced open-circuit voltage loss. [13] To date, solution-processed nonfullerene solar cells based on polymer-polymer (all-polymer) and polymer-small molecule blend have achieved power conversion efficiencies (PCEs) of 10% and 13%, respectively. [14][15][16][17][18][19] Exciton dissociation and charge transport are at the core of organic photovoltaics, which is strongly affected by the BHJ blend morphology. [20][21][22][23] In fullerene-based systems, the morphology of thin films is critical to the device performance and has been extensively studied. [24] How the blend morphology of nonfullerene blend affects device efficiency and stability is of growing interest as the PCEs of many nonfullerene solar cells now exceed the best fullerene devices. It is well known that the morphology has been largely influenced by the D:A blend ratio. Early studies on fullerene-based devices observed a drastic change in film morphology when fabricating the devices with increased acceptor content. [25][26][27][28] However, for nonfullerene solar cells, recent efforts mainly focus on materials synthesis and device optimization. To the best of our knowledge, systematical study on the effect of blend ratio on the device morphology, performance, and stability has not been reported, while it is of great importance to help achieve in-depth Tuning the blend composition is an essential step to optimize the power conversion efficiency (PCE) of organic bulk heterojunction (BHJ) solar cells. PCEs from devices of unoptimized donor:acceptor (D:A) weight ratio are generally significantly lower than optimized devices. Here, two high-performance organic nonfullerene BHJ blends PBDB-T:ITIC and PBDB-T:N2200 are adopted to investigate the effect of blend ratio on device performance. It is found that the PCEs of polymer-polymer (PBDB-T:N2200) blend are more tolerant to composition changes, relati...
Lead sulphide (PbS) nanocrystals (NCs) are promising materials for low-cost, high-performance optoelectronic devices. So far, PbS NCs have to be first synthesized with long-alkyl chain organic surface ligands and then be ligand-exchanged with shorter ligands (two-steps) to enable charge transport. However, the initial synthesis of insulated PbS NCs show no necessity and the ligand-exchange process is tedious and extravagant. Herein, we have developed a direct one-step, scalable synthetic method for iodide capped PbS (PbS-I) NC inks. The estimated cost for PbS-I NC inks is decreased to less than 6 $·g−1, compared with 16 $·g−1 for conventional methods. Furthermore, based on these PbS-I NCs, photodetector devices show a high detectivity of 1.4 × 1011 Jones and solar cells show an air-stable power conversion efficiency (PCE) up to 10%. This scalable and low-cost direct preparation of high-quality PbS-I NC inks may pave a path for the future commercialization of NC based optoelectronics.
Current efforts on lead sulfide quantum dot (PbS QD) solar cells are mostly paid to the device architecture engineering and postsynthetic surface modification, while very rare work regarding the optimization of PbS synthesis is reported. Here, PbS QDs are successfully synthesized using PbO and PbAc · 3H O as the lead sources. QD solar cells based on PbAc-PbS have demonstrated a high power conversion efficiency (PCE) of 10.82% (and independently certificated values of 10.62%), which is significantly higher than the PCE of 9.39% for PbO-PbS QD based ones. For the first time, systematic investigations are carried out on the effect of lead precursor engineering on the device performance. It is revealed that acetate can act as an efficient capping ligands together with oleic acid, providing better surface coverage and replace some of the harmful hydroxyl (OH) ligands during the synthesis. Then the acetate on the surface can be exchanged by iodide and lead to desired passivation. This work demonstrates that the precursor engineering has great potential in performance improvement. It is also pointed out that the initial synthesis is an often neglected but critical stage and has abundant room for optimization to further improve the quality of the resultant QDs, leading to breakthrough efficiency.
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