Control of Crystal Structures and Optical Properties with Hybrid Formamidinium and 2‑Hydroxyethylammonium Cations for Mesoscopic Carbon-Electrode Tin-Based Perovskite Solar Cells

Alcohol-based bifunctional ammonium cations, 2-hydroxyethylammonium (HEA+), HO­(CH2)2NH3+, were introduced into formamidinium (FA+) tin-based perovskites (HEAxFA1–xSnI3; x = 0–1) to absorb light in carbon-based mesoscopic solar cells. We found that HEA+ cations play a key role to control the crystal structures, the lattice structures altered from orthorhombic (x = 0) to rhombohedral (x = 0.2–0.4) with greater symmetry. When x was increased to 0.6–1.0, tin and iodide vacancies were formed to generate 3D-vacant perovskites (HEAxFA1–xSn0.67I2.33, x ≥ 0.6) with a tetragonal structure. Tin-based perovskites in this series were fabricated into mesoporous solar cells using one-step drop-cast (DC), two-step solvent-extraction (SE), and SE + 3% ethylenediammonium diiodide (EDAI2) as an additive. After optimization of device performance with the SE + 3% EDAI2 approach, the HEA0.4FA0.6SnI3 (HEAI = 40%) device gave the best photovoltaic performance with JSC = 18.52 mA cm–2, VOC = 371 mV, FF = 0.562, and overall efficiency η = 3.9% after the device was stored for a period of 340 h.

醇基双功能铵阳离子：2-羟乙基铵（2-hydroxyethylammonium, HEA+，化学式为HO(CH₂)₂NH₃⁺）被引入甲脒（formamidinium, FA+）基锡基钙钛矿体系（HEAₓFA₁₋ₓSnI₃；x取值范围为0~1），用于碳基介观太阳能电池的光吸收。研究发现，HEA+阳离子在调控晶体结构中发挥关键作用：晶格对称性显著提升，晶体结构从纯FA+体系（x=0）的正交晶相转变为x=0.2~0.4时的三方晶相。当x提升至0.6~1.0时，体系中会形成锡空位与碘空位，进而生成具有四方晶结构的三维空位型钙钛矿（HEAₓFA₁₋ₓSn₀.₆₇I₂.₃₃，x≥0.6）。本系列锡基钙钛矿可通过三种工艺制备为介观太阳能电池：一步滴涂法（drop-cast, DC）、两步溶剂萃取法（solvent-extraction, SE），以及添加3%乙二胺二碘化物（ethylenediammonium diiodide, EDAI₂）的SE改良工艺。通过优化SE+3% EDAI₂工艺的器件性能，当HEA掺杂摩尔占比为40%（对应组分为HEA₀.₄FA₀.₆SnI₃）时，器件在存储340小时后展现出最优光伏性能：短路电流密度（short-circuit current density, JSC）为18.52 mA·cm⁻²，开路电压（open-circuit voltage, VOC）为371 mV，填充因子（fill factor, FF）为0.562，光电转换效率（power conversion efficiency, η）达3.9%。