According to the detailed balanced limit for a singlejunction solar cell, tin−lead (Sn−Pb) perovskite solar cells (PSCs) can achieve power conversion efficiencies (PCEs) more than Pb-PSCs. However, the rise in PCE of Sn−Pb PSCs is limited by the choice of hole transport layer to PEDOT:PSS only. Inspired by the use of hole selective monolayers (HSM) in Pb only PSCs, here, we employed 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz), leading to PCE (21.39%) comparable to PSCs fabricated on conventional PEDOT:PSS (21.37%). Moreover, we reported a small molecule, methyl phosphonic acid (MPA), employing which an equipotential performance (PCE= 21.08%) was obtained owing to its passivation effect on the transparent conducting oxide (TCO) layer. Furthermore, by taking motivation from the idea of cosensitization in dye sensitized solar cells, we explored the point that the coabsorption of 2-(9H-carbazol-9-yl) ethyl] phosphonic acid (2PACz) and a small molecule MPA on TCO glass led to the Sn−Pb PSC (1.25 eV) with a PCE of 23.3% and open-circuit voltage of 0.88 V.

terms of employing the ideal bandgap absorber layer in PSC, the tin-lead (Sn-Pb) mixed PSCs are now getting attention with the additional benefit of utilizing them in tandem solar cell technology. [8][9][10] In recent years, various research groups have demonstrated power conversion efficiencies (PCEs) of more than 20% by employing Sn-Pb PSCs. [9,[11][12][13][14] However, PCE of Sn-Pb mixed PSCs is still lagging behind their Pb counterparts, especially in terms of open-circuit voltage (V oc ) loss, which is conventionally described as the deficit from the bandgap, is less than 0.3 V for the efficient Pb-PSCs. [4][5][6] Therefore, in the recent past, the efforts are directed toward finding the solutions to overcome the V oc loss. Researchers around the world are trying to address the problem by solving the issues related to the physical properties of the Sn-Pb perovskite films such as short carrier lifetime, [12] large Urbach energy, [11] high trap density, and most importantly the rapid oxidation of Sn 2+ to Sn 4+ . [9,13,14] The focus has been on improving the physical properties by employing different thin film formation strategies. Tong et al., [12] demonstrated the drastic improvement in optoelectronic properties such as the increase in carrier lifetime of more than 1 µs and carrier diffusion length of longer than 1 µm with the incorporation of bulky guanidinium thiocyanate (GuaSCN) into the perovskite films that led to the first research report of more than 20% PCE in Sn-Pb PSCs with a V oc loss of 0.42 V. The increase in PSC performance is assigned to the passivation by the formation of a 2D structure at the grain boundaries that also suppresses the formation of Sn vacancies. This kind of improvement in solar cell performance is the same observation as reported in the case of pure Pb-containing PSCs. [15] Our group also showed the effect of the decrease in trap densities, at the surface and bulk, by using strain engineering, steering to the PCE of 20.4%, and V oc loss of less than 0.50 V. [11] Recently, Li et al., [16] also demonstrated the importance of surface and grain boundary passivation by the formation of 1D pyrrolidine perovskite, a V oc loss of 0.41 V is reported. Lin et al., [9] addressed the oxidation problem in Sn-Pb precursor solution. The Sn metal is introduced as a reducing agent in precursor solution that decreased concentration of Sn 4+ (Sn 4+ + Sn→ 2Sn 2+ ) in the precursor solution before the film formation, Tin-lead perovskite solar cells (PSCs) show inferior power conversion efficiency (PCE) than their Pb counterparts mainly because of the higher open-circuit voltage (V oc ) loss. Here, it is revealed that the p-type surface of perovskite transforms to n-type, based on post-treatment by a Lewis base, ethylenediamine. This approach forms a graded band structure owing to the rise of the Fermi-energy level at the surface of the perovskite layer, and increases the built-in potential from 0.56 to 0.76 V, which increases the V oc by more than 100 mV. It is demonstrated that EDA can lower the ...

Many efforts have been made towards improving perovskite (PVK) solar cell stability, but their thermal stability, particularly at 85 °C (IEC 61646 climate chamber tests), remains a challenge. Outdoors, the installed solar cell temperature can reach up to 85 °C, especially in desert regions, providing sufficient motivation to study the effect of temperature stress at or above this temperature (e.g., 100 °C) to confirm the commercial viability of PVK solar cells for industrial companies. In this work, a three-layer printable HTM-free CH NH PbI PVK solar cell with a mesoporous carbon back contact and UV-curable sealant was fabricated and tested for thermal stability over 1500 h at 100 °C. Interestingly, the position of the UV-curing glue was found to drastically affect the device stability. The side-sealed cells show high PCE stability and represent a large step toward commercialization of next generation organic-inorganic lead halide PVK solar cells.

Tin-doped indium oxide (ITO) sputtering is known as a damaging cause on organic hole transporting material in solar cells. In order to gain more insights into the reasons for poor device performance of perovskite solar cells by the ITO sputtering on Spiro-OMeTAD, here we present an in-depth study by I−V simulation analysis using corresponding equivalent circuit models. First, experimental I−V data were obtained for the perovskite solar cells with ⟨FTO/TiO 2 (dense)/ TiO 2 (mesoporous)/CH 3 NH 3 PbI 3 /Spiro-OMeTAD/ITO/Au⟩ configuration. An Au layer (t = 50 nm) was deposited on the ITO as a contact layer. The simulation studies indicated that sputtering of ITO onto Spiro-OMeTAD introduced a reverse Schottky diode and an additional diode to the device that could be relating the sputtering damage of the Spiro-OMeTAD layer. By considering the parameter of the reverse diode element as a function of sputtering time, it was found that the barrier height of the reverse Schottky diode was enhanced by the sputtering damage against Spiro-OMeTAD, which could be the key reason for the reduced fill factor of the devices.

Research of CH3NH3PbI3 perovskite solar cells had significant attention as the candidate of new future energy. Due to the toxicity, however, lead (Pb) free photon harvesting layer should be discovered to replace the present CH3NH3PbI3 perovskite. In place of lead, we have tried antimony (Sb) and bismuth (Bi) with organic and metal monovalent cations (CH3NH3 +, Ag+ and Cu+). Therefore, in this work, lead-free photo-absorber layers of (CH3NH3)3Bi2I9, (CH3NH3)3Sb2I9, (CH3NH3)3SbBiI9, Ag3BiI6, Ag3BiI3(SCN)3 and Cu3BiI6 were processed by solution deposition way to be solar cells. About the structure of solar cells, we have compared the normal (n-i-p: TiO2-perovskite-spiro OMeTAD) and inverted (p-i-n: NiO-perovskite-PCBM) structures. The normal (n-i-p)-structured solar cells performed better conversion efficiencies, basically. But, these environmental friendly photon absorber layers showed the uneven surface morphology with a particular grow pattern depend on the substrate (TiO2 or NiO). We have considered that the unevenness of surface morphology can deteriorate the photovoltaic performance and can hinder future prospect of these lead-free photon harvesting layers. However, we found new interesting finding about the progress of devices by the interface of NiO/Sb3+ and TiO2/Cu3BiI6, which should be addressed in the future study.