With the rapid increase of efficiency up to 22.1% during the past few years, hybrid organic-inorganic metal halide perovskite solar cells (PSCs) have become a research “hot spot” for many solar cell researchers. The perovskite materials show various advantages such as long carrier diffusion lengths, widely-tunable band gap with great light absorption potential. The low-cost fabrication techniques together with the high efficiency makes PSCs comparable with Si-based solar cells. But the drawbacks such as device instability, J-V hysteresis and lead toxicity reduce the further improvement and the future commercialization of PSCs. This review begins with the discussion of crystal and electronic structures of perovskite based on recent research findings. An evolution of PSCs is also analyzed with a greater detail of each component, device structures, major device fabrication methods and the performance of PSCs acquired by each method. The following part of this review is the discussion of major barriers on the pathway for the commercialization of PSCs. The effects of crystal structure, fabrication temperature, moisture, oxygen and UV towards the stability of PSCs are discussed. The stability of other components in the PSCs are also discussed. The lead toxicity and updated research progress on lead replacement are reviewed to understand the sustainability issues of PSCs. The origin of J-V hysteresis is also briefly discussed. Finally, this review provides a roadmap on the current needs and future research directions to address the main issues of PSCs.

Commercial solar cells have a power conversion efficiency (PCE) in the range of 10–22% with different light absorbers. Graphene, with demonstrated unique structural, physical, and electrical properties, is expected to bring the positive effects on the development of thin film solar cells. Investigations have been carried out to understand whether graphene can be used as a front and back contacts and active interfacial layer in solar cell fabrication. In this review, the current progress of this research is analyzed, starting from the graphene and graphene-based Schottky diode. Also, the discussion was focused on the progress of graphene-incorporated thin film solar cells that were fabricated with different light absorbers, in particular, the synthesis, fabrication, and characterization of devices. The effect of doping and layer thickness of graphene on PCE was also included. Currently, the PCE of graphene-incorporated bulk-heterojunction devices have enhanced in the range of 0.5–3%. However, device durability and cost-effectiveness are also the challenging factors for commercial production of graphene-incorporated solar cells. In addition to the application of graphene, graphene oxides have been also used in perovskite solar cells. The current needs and likely future investigations for graphene-incorporated solar cells are also discussed.

Graphene films were synthesized and characterized to demonstrate their potential applications as the transparent electrodes in photovoltaic devices. Graphene films were prepared by chemical vapor deposition of graphene on copper substrates followed by transferring them onto the desired substrates. The quality and uniformity graphene transferred onto different substrates were characterized by Raman spectroscopy and UV-VIS-NIR reflectance as well as transmission spectroscopy. The results showed that the films synthesized contained 1-3 layers of graphene with the sheet resistance and optical transparency in the ranges of 50-350 sq /  and 85-95 %, respectively. Thin films of cadmium sulfide (CdS) were deposited on different substrates by chemical bath deposition method to study the optoelectronic behavior at the interface of graphene/CdS. The results showed that transient response time and the magnitude of photocurrent were enhanced by the graphene electrodes. The order of photocurrent merit was found to be CdS/graphene /Glass > CdS/ITO/glass, indicating that the CdS/graphene stack is to be the most efficient electron transport matrix for the separation of photo excited carriers in the CdS films.

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