Abstract-The Internet of Things (IoT) being a promising technology of the future is expected to connect billions of devices. The increased number of communication is expected to generate mountains of data and the security of data can be a threat. The devices in the architecture are essentially smaller in size and low powered. Conventional encryption algorithms are generally computationally expensive due to their complexity and requires many rounds to encrypt, essentially wasting the constrained energy of the gadgets. Less complex algorithm, however, may compromise the desired integrity. In this paper we propose a lightweight encryption algorithm named as Secure IoT (SIT). It is a 64-bit block cipher and requires 64-bit key to encrypt the data. The architecture of the algorithm is a mixture of feistel and a uniform substitution-permutation network. Simulations result shows the algorithm provides substantial security in just five encryption rounds. The hardware implementation of the algorithm is done on a low cost 8-bit micro-controller and the results of code size, memory utilization and encryption/decryption execution cycles are compared with benchmark encryption algorithms. The MATLAB code for relevant simulations is available online at https://goo.gl/Uw7E0W.

The wide bandgap Sb 2 S 3 is considered to be one of the most promising absorber layers in single-junction solar cells and a suitable top-cell candidate for multi-junction (tandem) solar cells. However, compared to mature thinfilm technologies, Sb 2 S 3 based thin-film solar cells are still lagging behind in the power conversion efficiency race, and the highest of just 7.5% has been achieved to date in a sensitized single-junction structure. Furthermore, to break single junction solar cell based Shockley-Queisser (S-Q) limits, tandem devices with wide bandgap top-cells and low bandgap bottom-cells hold a high potential for efficient light conversion. Though matured and desirable bottom-cell candidates like silicon (Si) are available, the corresponding mature wide bandgap top-cell candidates are still lacking. Hence, a literature review based on Sb 2 S 3 solar cells is urgently warranted. In this review, the progress and present status of Sb 2 S 3 solar cells are summarized. An emphasis is placed mainly on the improvement of absorber quality and device performance. Moreover, the low-performance causes and possible overcoming mechanisms are also explained. Last but not least, the potential and feasibility of Sb 2 S 3 in tandem devices are vividly discussed. In the end, several strategies and perspectives for future research are outlined.

Antimony sulfide (Sb2S3) is a promising photoelectric material because of its wide bandgap approximately 1.7 eV for next‐generation solar cells, high optical absorption coefficient, and its green and earth‐abundant constituents. Different to traditional cubic structure photovoltaic materials, Sb2S3 holds one‐dimensional crystal structure and its thin film with [hk1] preferred orientation shows one‐order‐higher carrier transport mobility. However, all the reported Sb2S3 films exhibited [hk0] preferred orientation on CdS‐based superstrate device structure up to now. Thus, it is indispensable to study the controllable‐orientations Sb2S3 film deposition and the relationship between the orientation and performances. In this paper, we develop a vertical vapor transport deposition (V‐VTD) method, which can tune the preferred orientation of Sb2S3 thin film from [hk0] to [hk1] by reaction recipe monitoring. Combining the experiment results, a reasonable deposition/reevaporation competing model is suggested to explain above orientation conversion mechanism. The device efficiency increases from less than 2% to about 4% with the orientation of Sb2S3 film changing from [hk0] to [hk1]. By fine regulating the technique of deposition, the device with [hk1] orientation has better crystallinity, lower interface recombination, and higher built‐in voltage comparing with the [hk0] one. Finally, a champion power conversion efficiency (PCE) of 4.5% has been achieved, and the VOC of 730 mV is the top value among the Sb2S3 solar cells. The present versatile orientation tuning strategy could overcome the bottleneck of strong anisotropic materials and show high potential for noncubic material deposition and related optoelectronic device performance enhancement.