Lead‐Free Solar Cells based on Tin Halide Perovskite Films with High Coverage and Improved Aggregation

Abstract

Tw osimple methods to improve tin halide perovskite film structure are introduced, aimed at increasing the power conversion efficiency of lead free perovskite solar cells.F irst, ah ot antisolvent treatment (HAT) was found to increase the film coverage and prevent electrical shunting in the photovoltaic device.Second, it was discoveredthat annealing under alow partial pressure of dimethyl sulfoxide vapor increased the average crystallite size. The topographical and electrical qualities of the perovskite films are substantively improved as aresult of the combined treatments,facilitating the fabrication of tin-based perovskite solar cell devices with power conversion efficiencies of over 7%.Metal halide perovskite solar cells (PSCs) have gained tremendous attention in the past few years,w ith certified efficiencies reaching 23.3 %. [1] However,t he toxicity of lead (Pb), commonly used in high efficiency PSCs,r emains as erious problem that hampers the wide application of this "magic" material. Replacing Pb 2+ with environmentally friendly cations,s uch as germanium (II) (Ge 2+ ), tin (II) (Sn 2+ ), and bismuth (III) (Bi 3+ ), is therefore an important priority. [2][3][4][5] Theoretical calculations indicate that the perovskite crystal structure is preserved after metal cation substitution. [6] As the most promising candidate among Pb-free perovskites,t in halide perovskites show suitable band gaps and advantageous optoelectronic properties. [2][3][4][5][6][7] Unfortunately,p ower conversion efficiencies (PCEs) obtained from Sn-based PSCs are much lower than that of their Pb counterpart. Though aS n-based PSC using MASnI 3 as the absorber was first demonstrated in 2014 with ar eported power conversion efficiencyo ver 5%, [8,9] theh ighest PCE achieved for aS n-based PSC to date is still below 10 %. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Rapid oxidation of Sn 2+ to Sn 4+ in ambient atmosphere dopes the perovskite layer into high conductivity,r esulting in severe electrical shunting. [4,9] Similar shorting issues also predominate when the perovskite film is fabricated with uneven thickness or pinholes,acommon occurrence for Sn-based PSCs. [18] Despite the clear need to improve device performance,only alimited number of groups are investigating Snbased PSC at present. Thed ifficulty in fabricating highquality Sn perovskite films is as ignificant impediment. [15][16][17][18][19] In this paper we focus on the development of reliable procedures for fabricating uniform, continuous," pinhole free" Sn perovskite films with large grain size and good electrical properties-desirable traits which can be expected to lead to efficient and reproducible Sn-based PSCs.T echniques to optimize the formation of nucleation sites and control the crystal growth process are introduced. With the first technique,w hich we call "hot antisolvent treatment" (HAT), antisolvent is pre-heated to improve the film coverage during spin coating,e liminating the large pinholes observed when the antisolvent is used at room t...

Sn(IV)-free tin perovskite films realized by in situ Sn(0) nanoparticle treatment of the precursor solution

“…1). This particular perovskite formula was selected for its optimal charge extraction when paired with common hole transport materials such as PEDOT:PSS 15,34 . Following the widely used method for tin perovskite film formation, 10 mol% SnF 2 was also added to the precursor solution containing SnI 2 , FAI, and MAI.…”

“…SnF 2 is an additive which is important for the film growth control. The perovskite films were fabricated with our hot antisolvent treatment (HAT), which improves the film coverage 15 . No difference in the X-ray diffraction (XRD) patterns was observed for the films prepared from different SnI 2 sources ( Supplementary Fig.…”

“…Several strategies have been pursued to improve the performance of Sn-based PSCs, including solvent engineering [13][14][15] , crystal growth control 16 , and compositional variation [17][18][19] . Various reductants including hypophosphorous acid 20 , hydrazine vapor 21 , Sn bulk powder 22 , and hydroquinone sulfonic acid 23 were found to be moderately effective in decreasing the concentration of Sn(IV).…”

Efficient Passivation Strategy on Sn Related Defects for High Performance All‐Inorganic CsSnI3 Perovskite Solar Cells

“…[ 5 ] As the most promising alternative, Sn‐based perovskites outperform all of the currently reported Pb‐free perovskites in terms of photovoltaic performance. [ 6–13 ] In an Sn‐based perovskite material system, the all‐inorganic CsSnI 3 with native inorganic structural stability, favorable direct bandgap (1.3 eV), extra‐low exciton binding energy (18 meV), and excellent optical absorption coefficient (10 4 cm –1 comparable to that of MAPbI 3 ), is the most investigated Sn‐based semiconductor material for photovoltaic applications. [ 14–16 ] However, compared with hybrid MASnI 3 and FASnI 3 PSCs of a significant leap in PCE over 10%, the potential application of all‐inorganic CsSnI 3 PSCs seriously suffered from the limitation of a low PCE of only around 5%.…”

Antisolvents in Perovskite Solar Cells: Importance, Issues, and Alternatives

“…used preheated chlorobenzene as antisolvent to fabricate FA 0.75 MA 0.25 SnI 3 based perovskite film. [ 103 ] It has been observed that at elevated temperature the miscibility between antisolvent (chlorobenzene) and perovskite precursor solvent (DMSO) increases, which enhanced the efficiency of the antisolvent, i.e., faster nucleation rate. At optimum preheat temperature (65 °C), chlorobenzene performed best producing very dense, smooth perovskite film.…”