Tin‐Lead Perovskite Fabricated via Ethylenediamine Interlayer Guides to the Solar Cell Efficiency of 21.74%

Abstract

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 ...

Development of formamidinium lead iodide-based perovskite solar cells: efficiency and stability

“…40 Both pure Sn and Sn–Pb show better charge transport performance than that of Pb-based perovskites, 96–98 and the highest efficiency reaches 21.74%. 99 Moreover, compared to the voltage loss of Pb-based perovskites, the voltage loss of the Sn–Pb perovskite can now be 0.33 V, which is comparable to that of FAPbI 3 -based devices. 100 The carrier lifetime has reached more than 1 μs.…”

Sn‐Pb Mixed Perovskites with Fullerene‐Derivative Interlayers for Efficient Four‐Terminal All‐Perovskite Tandem Solar Cells

“…[ 1–3 ] This technology promises to combine the ease of high efficiencies with low‐temperature fabrication and solution processing. [ 3,4 ] Despite the impressive power conversion efficiencies (PCEs) exceeding 25% for both all‐perovskite four‐terminal (4T) and two‐terminal tandem solar cells, [ 4,5 ] the low performance and stability of NBG perovskite sub‐cells (with current record PCEs of ≈21.7% [ 3–7 ] ) still possesses a major hurdle in the exploitation of this all‐thin‐film tandem technology. [ 1,4 ]…”

Stability of Tin- versus Lead-Halide Perovskites: Ab Initio Molecular Dynamics Simulations of Perovskite/Water Interfaces

“…Tin-halide perovskites (THPs) have emerged as one of the most promising lead-free alternative for photovoltaics 10 − 12 with record efficiencies of 14.6% 13 in pure THPs and beyond 20% in mixed tin–lead perovskites. 14 − 17 Despite having an optimal band gap (∼1.2–1.3 eV) for photovoltaic applications, THP performance and stability are still behind their lead-based counterpart. One of the critical aspects limiting the performance and the stability of THPs is the facile oxidation of Sn(II) to Sn(IV), 18 , 19 which may induce a large self-p-doping in the perovskite bulk and deep electron trap states at the perovskite surface.…”