Efficient Lead-Free Solar Cells Based on Hollow {en}MASnI₃ Perovskites

Abstract

Tin-based perovskites have very comparable electronic properties to lead-based perovskites and are regarded as possible lower toxicity alternates for solar cell applications. However, the efficiency of tin-based perovskite solar cells is still low and they exhibit poor air stability. Here, we report lead-free tin-based solar cells with greatly enhanced performance and stability using so-called "hollow" ethylenediammonium and methylammonium tin iodide ({en}MASnI) perovskite as absorbers. Our results show that en can improve the film morphology and most importantly can serve as a new cation to be incorporated into the 3D MASnI lattice. When the cation of en becomes part of the 3D structure, a high density of SnI vacancies is created resulting in larger band gap, larger unit cell volume, lower trap-state density, and much longer carrier lifetime compared to classical MASnI. The best-performing {en}MASnI solar cell has achieved a high efficiency of 6.63% with an open circuit voltage of 428.67 mV, a short-circuit current density of 24.28 mA cm, and a fill factor of 63.72%. Moreover, the {en}MASnI device shows much better air stability than the neat MASnI device. Comparable performance is also achieved for cesium tin iodide solar cells with en loading, demonstrating the broad scope of this approach.

Potential Substitutes for Replacement of Lead in Perovskite Solar Cells: A Review

“…The doping of bismuth‐based perovskite Cs 3 Bi 2 I 9 films with N,N‐dimethyl formamide/hydroiodide (HI) solution featured a pure crystalline film with an excellent thermal stability . PTAA employed as a HTM in ethylene diammonium and methylammonium tin iodide en[MASnI 3 ] has reported a SPCE of 6.63% with a very high current density of 24.3 mA cm −2 in a device architecture of FTO/C‐TiO 2 /mp‐TiO 2 /en[MASnI 3 ]/PTAA/Au . Many research groups have synthesized lead‐free MASnI 3 , FASnI 3 , and CsSnI 3 perovskite solar devices by using PTAA as a HTM.…”

Lead-free hybrid perovskites for photovoltaics

“…The quality of MASnI 3 films as components of solar cells can be ameliorated by introducing ethylenediamine (en) acting simultaneously as an additional organic cation in the HP lattice and as a morphology-directing agent [71]. The cells with such modified MASnI 3 absorbers showed a PCE of 6.63% (Table 1) with a relatively high FF of ≈64% (Fig.…”

“…(a) Reprinted with permission from [71], copyright 2017 American Chemical Society; (b) Reprinted with permission from [80], copyright 2017 American Chemical Society; (c) Reprinted with permission from [118], copyright 2017 American Chemical Society.…”

Tailoring the Band Gap in 3D Hybrid Perovskites by Substitution of the Organic Cations: (CH3NH3)1−2y(NH3(CH2)2NH3)2yPb1−yI3 (0≤y≤0.25)

“…The change of the band gap, the reduced density, and the under‐occupation of the Sn sites (refinement of single‐crystal data) were explained in terms of Schottky defects (i.e., missing SnI 2 /SnI + ), so they described the crystal structure as a “hollow 3D perovskite”. The same group published similar results for the system of H 2 en with MASnI 3 . In order to explain the reduced density, the amount of Schottky defects is expected to be in the region of 5–10 %, which is an uncommonly high value for such defects.…”