Diammonium Cations in the FASnI₃ Perovskite Structure Lead to Lower Dark Currents and More Efficient Solar Cells

Abstract

Hybrid halide perovskite solar cells with mixed cations demonstrate superior optical and electrical properties, especially for lead-based perovskite devices. Here, we report leadfree tin-based perovskite solar cells with diammonium cations, which can significantly improve the device performance. Formamidinium tin iodide (FASnI 3 ) perovskite can incorporate propylenediammonium (PN) and trimethylenediammonium (TN) and retain its three-dimensional structure while at the same time providing better film morphology and optoelectronic properties. As a result, solar cell devices using FASnI 3 absorbers mixed with 10% PN and 10% TN achieve higher power conversion efficiencies of 5.85% and 5.53%, respectively, compared to 2.53% of the pristine FASnI 3 solar cell. This difference in device performance can be mainly attributed to the reduced leakage current, lower trap-state density, and reduced recombination, as evidenced by our dark current−voltage, space-charge-limited current, and impedance measurements. The results suggest that perovskite absorbers with mixed diammonium cations are beneficial in achieving high-performance perovskite solar cells.

Realizing High Efficiency over 20% of Low‐Bandgap Pb–Sn‐Alloyed Perovskite Solar Cells by In Situ Reduction of Sn4+

“…The dark I–V curves of the solar cells without and with Sn 4+ reduction have also been measured, as shown in Figure S8, Supporting Information. The device with Sn 4+ reduction shows lower dark current at negative and positive bias voltages compared with the device without Sn 4+ reduction, suggesting improved charge transport and decreased recombination loss in the device, which is also in line with the reduced nonradiative recombination rate γ . The results of simulations by the modified detailed balance model and dark I – V characteristics have further confirmed that the reduction of Sn 4+ by Sn powder has substantially reduced the trap density of the mixed Pb–Sn perovskite films and finally led to the outstanding device performance of low‐bandgap mixed Pb–Sn PSCs.…”

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

“…Copyright 2018, Royal Society of Chemistry. k) Device structure, l) J – V curves, m) EQE curves, and n) PCE statistics of the FASnI 3 solar cells with and without 10% PN and 10% TN; Reproduced with permission . Copyright 2018, American Chemical Society.…”

“…The FASnI 3 perovskite light absorbers incorporated with a diammonium cation such as propylenediammonium (PW) and trimethylenediammonium (TN) display better efficiency than the pristine FASnI 3 solar cell. The FASnI 3 light absorbers mixed with 10% TN and 10% PN displayed a SPCE of 5.53 and 5.58% with a better film morphology along with retaining their 3D perovskite structure . Figure shows the (k) device structure, (l) J –V curves, (m) EQE curves, and (n) PCE statistics of the FASnI 3 solar cells with and without 10% PN and 10% TN .…”

Synergy Effect of Both 2,2,2‐Trifluoroethylamine Hydrochloride and SnF2 for Highly Stable FASnI3−xClx Perovskite Solar Cells

“…The increase in the V oc can be attributed to the reduction in Sn 4+ concentration which would result in a decrease in the carrier concentration and consequently reduced recombination and increased V oc . The space charge limited current (SCLC) method is used to evaluate the trap‐state density ( n t ) in the control and optimal perovskite films (see Supporting Information for details) . As shown in Figure S6, Supporting Information, the V TFL values of the devices without and with 5.0% TFEACl are around 0.22 and 0.14 V, respectively.…”

“…Common approach is to use different additives to suppress the formation of Sn 4+ and thus reduce the hole density in the films, as well as improve the film uniformity and coverage. A variety of different additives have been reported to date, including various organic ammonium iodides, SnF 2 , and various reducing agents . The addition of SnF 2 , alone or combined with other additives, is a common approach to inhibit the formation of Sn 4+ and improve the film morphology.…”