近年来,钙钛矿太阳能电池(perovskite solar cells,PSCs)凭借其优异的光电性能、低廉的成本、相对简单的制备工艺和较高的能量转换效率(power conversion efficiency,PCE)等优点,吸引了大量研究人员的关注.其中,拥有良好的热、湿度稳定性和优异光电性能的全无机CsPbBr3钙钛矿太阳能电池逐渐成为近年来的研究热点.尽管如此,由于难以找到一种能同时以高浓度溶解PbBr2与CsBr的溶剂,全无机钙钛矿太阳能电池的CsPbBr3薄膜通常使用两步旋涂法制备.在两步旋涂法中,采用水作为CsBr的溶剂,不仅可以提高CsBr在溶液中的溶解度,还可以减少对环境的破坏.然而,使用CsBr水溶液制备的CsPbBr3太阳能电池存在钙钛矿薄膜不均匀、易有杂相生成、成膜不易控制等问题,这些问题将导致此类CsPbBr3太阳能电池出现不良性能.基于此,本课题从绿色、提高钙钛矿薄膜结晶性出发,提出了 一种高效简便的水溶液前驱体添加剂方法,使用NBA作为绿色添加剂,制备出的钙钛矿晶相更纯净,薄膜晶粒尺寸愈加均匀饱满,钙钛矿层更加致密光滑,光吸收与载流子寿命也更长的高性能器件.经过各项实验参数的探究,最终确定以1.175 mol L-1,NBA体积分数为5％的CsBr溶液、预加载时间15s、退火温度250℃、退火时间15 min所制备的电池器件性能最优,其最高PCE为9.92％,开路电压(open-circuit voltage,VOC)为1.60V,短路电流密度(short circuit current density,JSC)为7.23 mA cm-2,填充因子(fill factor,FF)为85.78％.
Fabrication of CsPbBr3 perovskite solar cells with n-butanol additives
Perovskite solar cells(PSCs)have garnered notable attention in the photovoltaic field for their cost-effectiveness,simple fabrication,and high power conversion efficiency(PCE).Since the inception of the first PSC in 2009,significant advancements have been made,with the PCE soaring from 3.8％to 26.1％,nearly matching the efficiency of conventional silicon-based solar cells.Among PSCs,all-inorganic CsPbBr3 PSCs have emerged as a subject of keen interest owing to their exceptional stability in thermal and humid conditions,in contrast to organic-inorganic PSCs that utilize MAPbBr3 as light-harvesting materials,which have a limited lifespan due to the instability of organic ammonium cations in the composition.The fabrication of all-inorganic CsPbBr3 PSCs typically involves a two-step spin-coating method,in which the PbBr2 layer is initially deposited on fluorine-doped tin oxide conductive glass with an electron or hole transport layer.Subsequently,the CsBr solution is spin-coated onto the PbBr2 layer and annealed to form the CsPbBr3 layer.Unlike methanol,the CsBr is dissolved in water at a high concentration to ensure complete reaction with PbBr2 without causing environmental pollution issues.However,the suboptimal contact between water and PbBr2 films poses a challenge to the development of PSCs and may result in the generation of more defects and excess CsBr.Consequently,an additive is required for the CsBr aqueous solution to enhance the quality of the perovskite film produced through the two-step spin-coating method,facilitating the uniform spread of the solution on the PbBr2 film and promoting evaporation to achieve larger CsPbBr3 grains while inhibiting defects.Consequently,water is utilized to dissolve the CsBr at a high concentration,while employing various volume fractions of additives,reaction times,and annealing durations.It is observed that the utilization of a 1.175 molL-1 CsBr aqueous solution with a 5％volume fraction of n-butanol(NBA)on the PbBr2 film,a reaction period of 15 s prior to spin-coating,and an annealing duration of 15 min at 250℃,yields a better morphology and photovoltaic performance compared to the pristine one,solely comprising CsBr aqueous solution.The principal findings and discussions are outlined below:(1)The NBA-doped CsPbBr3 film exhibits fewer defects and heterophase compared to the pristine film in morphology,as evidenced by scanning electron microscope(SEM)and X-ray diffraction(XRD)measurements.This indicates that the introduction of a 5％volume of NBA enhances the wettability of the CsBr aqueous solution,facilitating improved contact with the PbBr2 film,and offering additional nucleation sites due to the boiling point difference between water and NBA.(2)In the electrochemical and optical tests,the NBA-doped group exhibits a notable decrease in defect density,effectively mitigating nonradiative charge-carrier recombination.This enhancement is conducive to improving the extraction and mobility of photogenerated carriers,consequently enhancing both the Voc and PCE of the PSCs.The moderate incorporation of NBA improves the growth of CsPbBr3 grains and facilitates the reaction between PbBr2 and CsBr,thereby ameliorating the defects within the perovskite film.This process leads to the development of larger grains,thereby promoting radiative charge-carrier combination and culminating in superior PSC performance.(3)The PSCs with the configuration of FTO/TiO2/CsPbBr3/Carbon are fabricated.The NBA-doped PSC can achieve an optimal PCE of 9.92％accompanied by a Voc of 1.60 V,FF of 85.78％,and Jsc of 7.23 mA cm-2,which is a significant improvement compared to that of the undoped-device(6.80％).Moreover,the stability of these devices has markedly increased,as evidenced by the fact that after 28 days,the PCE of the optimum device remains above 95％.
all-inorganic perovskite solar cellsCsPbBr3solvent engineeringn-butanoltwo-step spin-coating
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