The electron transport layer plays a key role in affecting the charge dynamics and photovoltaic parameters in perovskite solar cells. Compared to other counterparts, SnO 2 has unique advantages such as low temperature fabrication and high electron extraction ability, and it receives extra attentions from the research community since the first report. Planar-type perovskite solar cells based on SnO 2 exhibit a simple architecture and state of art device can achieve a power conversion efficiency of over 23%, which can compete with traditional devices using mesoporous TiO 2. The modification engineering of SnO 2 has contributed significantly to the enhanced device performance during the past years. There is still great potential for further improvement in the efficiency and long-term stability. Herein recent advances toward modifying the optoelectronic properties of SnO 2 from the perspective of the optimization strategies are summarized and the remaining challenges as well as opportunities for future research are discussed. The continuous efforts dedicated to this exciting field may pave the way for developing commercial perovskite solar cells.

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Several lepidopteran species share the same pheromone blend consisting of (Z)-11-hexadecenal (Z11-16:Ald) and (Z)-9-hexadecenal (Z9-16:Ald) at different ratios and active doses. In rice pest Chilo suppressalis, (Z)-11-hexadecenol, (Z11-16:OH) and octadecanal (18:Ald) were identified as minor components in the pheromone gland of female moths, and these components were previously not considered as part of the sex pheromone of C. suppressalis. Z11-16:Ald, Z9-16:Ald and (Z)-13-octadecenal (Z13-18:Ald) frequently trapped other lepidopteran species, such as rice pests Scirpophaga incertulas and Mythimna separate, corn and vegetable pests Helicoverpa armigera in the field, suggesting a lack of specificity in the pheromone blend. Our data showed that the minor component Z11-16:OH did not have a synergistic effect on the attractiveness of the blend to C. suppressalis; however, pheromone mixtures containing Z11-16:OH failed in trapping male H. armigera moths. We confirmed the identity and specificity of the C. suppressalis sex pheromone and demonstrated that Z11-16:OH plays a key role in the reproductive isolation of C. suppressalis, M. separata, and H. armigera moths, and a similar role of Z9-18:Ald in that of S. incertulas and C. suppressalis. This phenomenon could be more widely applicable to interspecific interactions in the pheromone communication between insects, which is crucial to developing the electronic automatic counting device for automatically monitoring the pest population by pheromone trapping based on its species specificity.