Hole transporting material (HTM) is a significant component to achieve the high performance perovskite solar cells (PSCs). Over the years, inorganic, organic and hybrid (organic-inorganic) material based HTMs have been developed and investigated successfully. Today, perovskite solar cells achieved the efficiency of 22.1 % with with 2,2',7,7'-tetrakis(N,Ndi-p-methoxyphenyl-amine) 9,9-spirobifluorene (spiro-OMeTAD) as HTM. Nevertheless, synthesis and cost of organic HTMs is a major challenging issue and therefore alternative materials are required. From the past few years, inorganic HTMs showed large improvement in power conversion efficiency (PCE) and stability. Recently CuO x reached the PCE of 19.0% with better stability. These developments affirms that inorganic HTMs are better alternativesto the organic HTMs for next generation PSCs. In this report, we mainly focussed on the recent advances of inorganic and hybrid HTMs for PSCs and highlighted the efficiency and stability of PSCs improved by changing metal oxides as HTMs. Consequently, we expect that energy levels of these inorganic HTMs matches very well with the valence band of perovskites and improved efficiency helps in future practical deployment of low cost PSCs.

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Although the efficiency of Dye‐sensitized and Perovskite solar cell is still below the performance level of market dominance silicon solar cells, in last few years they have grabbed significant attention because of their fabrication ease using low‐cost materials, and henceforth these cells are considered as a promising alternative to commercial photovoltaic devices. However, third generation solar cells have significant absorption in the visible region of solar spectrum, which confines their power conversion efficiency. Subsequently, the performance of current photovoltaics is significantly hampered by the transmission loss of sub‐band‐gap photons. To overcome these issues, rare earth doped luminescent materials is the favorable route followed to convert these transmitted sub‐band‐gap photons into above‐band‐gap light, where solar cells typically have significant light‐scattering effects. Moreover, the rare earth based down/up conversion material facilitates the improvement in sensitization, light‐scattering and device stability of these devices. This review provides insight into the application of various down/up conversion materials for Dye‐sensitized and perovskite solar cell applications. Additionally, the paper discusses the techniques to improve the photovoltaic performance in terms of current density and photo voltage in detail.

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Conversion of near-infrared (NIR) light photons into visible light has remarkable advantages in dye sensitized solar cells (DSSCs) for their improved performance. This study uncovers the dual function of LiYF 4 :Er 3+ /Yb 3+ as upconverter (UC) and light scattering material in DSSCs by its incorporation onto the photoelectrode. The LiYF 4 :Er 3+ /Yb 3+ powders were prepared using a facile hydrothermal process followed by spin deposition of LiYF 4 :Er 3+ /Yb 3+ suspensions over photoelectrode. The photoelectrode used for this investigation was further cosensitized with N719 and squaraine SPSQ2 dyes. The dual functions of LiYF 4 :Er 3+ /Yb 3+ material coupled with dye cosensitization treatment produced record power conversion efficiency (PCE) of 10.53% in the fabricated DSSC. The LiYF 4 :Er 3+ /Yb 3+ enabled the photoelectrode DSSC to exhibit good short-circuit current density (J sc ) of 22.16 mA/cm 2 , open-circuit voltage (V oc ) of 0.66 V, and fill factor (FF) of 0.72. This work is the debut attempt toward the application of a photoelectrode embedded with dual function and cosensitized materials to utilize lower energetic photons through the upconversion mechanism and improve absorption close to red wavelengths (absorption band 630−700 nm) through the dye cosensitization process.