Oriented Perovskite Crystal towards Efficient Charge Transport in FASnI₃ Perovskite Solar Cells

Abstract

Despite a higher power conversion efficiency (PCE) than other lead‐free perovskite solar cells (PSCs) due to intrinsically excellent optoelectronic properties and suitable bandgaps of tin (Sn) perovskites, Sn‐based PSCs still suffer from issues of stability and efficiency for practical applications. Herein, a novel strategy of tuning perovskite crystal orientation toward ≈45° with respect to the substrate by doping 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) into formamidinium tin iodide (FASnI3) is proposed, which facilitates charge transport in the perovskite film and consequent device performances. In addition, the incorporation of 2,3‐DAPAC into FASnI3 enables dense and smooth high‐quality perovskite films with less Sn vacancies. Applications of the 2,3‐DAPAC‐treated FASnI3 films into PSCs acquire a champion PCE of 7.23%, showing 37.2% enhancement compared with 5.27% of the control device. Moreover, the storage stabilities of both perovskite films and PSCs are significantly prolonged with improved film quality.

Rational Design of Additive with Suitable Functional Groups Toward High‐Quality FA0.75MA0.25SnI3 Films and Solar Cells

“…From Figure a, the main diffraction peaks at 14.1°, 24.8°, 28.0°, 32.3°, and 40.7° that assigned to the crystallographic planes (100), (120), (200), (122), and (222), respectively, confirm that the perovskite possesses the orthorhombic crystal structure and preferred orientation. [ 17,23 ] As C 6 H 7 NO or C 6 H 6 FNO is incorporated, the diffraction peak intensity of the FA 0.75 MA 0.25 SnI 3 perovskite film on the (100) and (200) crystal planes increase significantly, indicative of an obviously enhanced crystallinity. This indicates that the introduction of —OH and —NH 2 groups from C 6 H 7 NO and C 6 H 6 FNO effectively promotes the preferential growth of perovskite crystals along the [100] and [200] crystal directions.…”

“…At the same time, we observed that the PL intensity of the perovskite films increases significantly with the doping of C 6 H 7 NO or C 6 H 6 FNO additive (Figure 2c), which is especially obvious for the C 6 H 6 FNO doped film. In view of the fact that the functional groups of —OH and —NH 2 generally form a hydrogen bond with SnI 6 4− octahedron through OH⋯I and NH⋯I, [ 17,23,29 ] the effective passivation of these functional groups to the perovskite induces a significant increase in the PL intensity by reducing the charged traps and suppressing the nonradiative recombination loss assisted by the charged traps.…”

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] However, Sn 2þ in Sn-based perovskites is easily oxidized to Sn 4þ , leading to p-type doping and high background carrier density, which will cause a large amount of unnecessary nonradiation. [18][19][20][21][22][23][24][25] Moreover, due to the weak binding energy of the elements in the Sn-based perovskite, a large number of Sn and iodide vacancies appear, causing a large number of defects in the grains or at the boundaries, and leading to the films with pinholes and rough surfaces and a high carrier recombination rate, which results in a large open-circuit voltage (V oc ) loss greater than 0.7 eV. [26][27][28][29][30][31][32][33] The above reasons have induced a relatively low efficiency of Sn-based PSCs compared with those of lead-based ones.…”

“…In addition, considering the synergistic passivation of multiple functional groups, a multipoint passivation strategy is used. The incorporation of additives with multiple functional groups like —F and —NH 3 , [ 40 ] —COOH and —NH 3 + /—NH 2 , [ 23 ] and —OH and —NH 3 [ 17 ] has been demonstrated to effectively passivate grain boundaries of FASnI 3 films and form pinhole‐free homogeneous and stable Sn‐based perovskite films with a low Sn 4+ content. So herein, we choose the C 6 H 6 FNO molecule with both —OH and —NH 3 groups to improve perovskite film quality.…”

The Voltage Loss in Tin Halide Perovskite Solar Cells: Origins and Perspectives

“…proposed a novel molecule of 2,3‐diaminopropionic acid monohydrochloride (2,3‐DAPAC) with both carboxyl and diammonium groups into FASnI 3 . [ 123 ] The results showed that the molecule could not only effectively passivate defects, but also modulate the crystal orientation of perovskite, which made it tilt at 45° relative to the substrate and facilitated charge transport. Consequently, the incorporation of 2,3‐DAPAC into FASnl 3 resulted in dense and smooth perovskite films with less Sn 4+ content (Figure 7h,i).…”