Perovskite solar cells have shown an impressive efficiency improvement over the past ~ 10 years achieving ~ 23% to date. However, the lifetime and instability of device characteristics are real issues to understand and solve before scaling up and commercialisation of these devices. Researchers have attempted to understand the hysteresis behaviour of current-voltage (I-V) curves in terms of mechanisms such as migration of several ions across the device and the effects of electronic defects during measurements. This review contributes to this scientific debate by presenting similar behaviour observed and reported for devices based on inorganic semiconductors. In established inorganic semiconductor thin film solar cells, both short lifetime and hysteresis have been observed, described and understood in terms of effects of numerous electronic defect levels. Therefore, the situation may be very similar and it is important to identify and reduce defects to remove this undesirable behaviour from perovskite solar cells. After considering the wealth of experimental results reported in the literature, the conclusion made is the dominating mechanism of I-V hysteresis is due to electronic defects available within the device structure. Suggestions have been made for potential researchers to experimentally investigate the phenomenon in order to finally put an end to this debate. As the defect levels and their concentrations are reduced, the initial efficiency, stability and the lifetime of perovskite solar cells should improve further, beyond the current situation.
Perovskite solar cells exhibiting ~ 14-15% efficiency were experimentally measured using current-voltage (I-V) and capacitance-voltage (C-V) techniques in order to extract material and device properties, and understand the action of photovoltaic (PV) operation. Deep analyses were carried out on dark-and illuminated I-V curves, and dark C-V curves. Results were compared with those of graded bandgap solar cells fabricated on inorganic n-type window layers. These analyses according to a physicist's point of view lead to understand the perovskite solar cell as a graded bandgap solar cell built on a p-type window layer. I-V and C-V results show very similar behaviour and the principle of PV action is identical. Once the stability issues with perovskites are solved, these devices have very high potential of producing next generation solar cells reaching at least mid-20% efficiency values.
A new route for fabrication of photoactive materials in organic-inorganic hybrid solar cells is presented in this report. Photoactive materials by blending a semiconductive conjugated polymer with an organolead halide perovskite were fabricated for the first time. The composite active layer was then used to make planar heterojunction solar cells with the PCBM film as the electron-acceptor. Photovoltaic performance of solar cells was investigated by J-V curves and external quantum efficiency spectra. We demonstrated that the incorporation of the conjugated photoactive polymer into organolead halide perovskites did not only contribute to the generation of charges, but also enhance stability of solar cells by providing a barrier protection to halide perovskites. It is expected that versatile of conjugated semi-conductive polymers and halide perovskites in photoactive properties enables to create various combinations, forming composites with advantages offered by both types of photoactive materials.
Highly reproducible perovskite solar cells via controlling the morphologies of the perovskite thin films by the solution-processed two-step method. Journal of Materials Science: Materials in Electronics, 1-11.
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