Organic solar cells (OSCs) have developed progressively in efficiency over the last two decades. Though it is promising, this technology is still far from realizing its full prospect. One of the most important parameters that determine the efficiency of OSCs is the open-circuit voltage (V_OC), which represents the maximum voltage a solar cell can provide to an external circuit. Light harvesting materials employed in OSCs have an optical band gap of around 1.7 to 2.1 eV and yet the V_OC barely exceeds 1.0 V, which is approximately just half of the photon's original energy. By contrast, in inorganic counterparts such as Si, CIGS and GaAs, the difference is only 0.3 to 0.45 eV between the material bandgap and V_OC. Hence, to achieve higher power conversion efficiencies (PCEs) in OSCs, a detailed understanding of the origins of V_OC and the associated energetic loss mechanisms is indispensable. The presented review takes the opportunity to elaborate various governing mechanisms and factors affecting the V_OC from a comprehensive yet insightful standpoint. This report also provides a concise synthesis of intricate interdependencies among the factors influencing V_OC and highlights the potential research strategies to improve V_OC, rendering possible pathways to facilitate the viable commercialization of OSCs.

Organic–inorganic hybrid perovskite solar cells (PSCs) have emerged as a new class of optoelectronic semiconductors that revolutionized the photovoltaic research in the recent years. The perovskite solar cells present numerous advantages include unique electronic structure, bandgap tunability, superior charge transport properties, facile processing, and low cost. Perovskite solar cells have demonstrated unprecedented progress in efficiency and its architecture evolved over the period of the last 5–6 years, achieving a high power conversion efficiency of about 22% in 2016, serving as a promising candidate with the potential to replace the existing commercial PV technologies. This review discusses the progress of perovskite solar cells focusing on aspects such as superior electronic properties and unique features of halide perovskite materials compared to that of conventional light absorbing semiconductors. The review also presents a brief overview of device architectures, fabrication methods, and interface engineering of perovskite solar cells. The last part of the review elaborates on the major challenges such as hysteresis and stability issues in perovskite solar cells that serve as a bottleneck for successful commercialization of this promising PV technology.

Flower shaped nanostructures of an architypical transparent conducting oxide, SnO₂, have been synthesized by an electrospinning technique for the first time by precisely controlling the precursor concentration in a polymeric solution. The flowers were made up of nanofibrils of diameter ∼70–100 nm, which in turn consisted of linear arrays of single crystalline nanoparticles of size 20–30 nm. Mott–Schottkey analysis shows that flowers have an order of magnitude higher electron density compared with the fibers despite their chemical similarity. Dye-sensitized solar cells fabricated using the flowers showed a record open circuit voltage of ∼700 mV and have one of the highest photoconversion efficiencies so far achieved with SnO₂ and the iodide/triiodide electrolyte. The photoaction spectra and impedance spectroscopic measurements show that the flowers are characterized by a higher electron lifetime, owing to their enhanced crystallinity, compared to the conventional fibrous structure.