Study On Preparation And Stability Of CsPbI₂Br Perovskite Solar Cells

With the growing severity of the energy crisis and environmental pollution,along with the urgent need for green energy development in China,solar energy has garnered widespread attention from both government and researchers.Solar cells are one of the most effective ways to harness solar energy.The escalating demand for solar power generation has propelled the research focus towards novel solar cells.Among the latest generation of solar cells,Perovskite Solar Cells（PSCs）have demonstrated tremendous commercial potential due to their high performance and low-cost advantages.Despite the power conversion efficiency（PCE）of organic-inorganic hybrid PSCs surpassing26%,stability remains a major factor hindering their commercialization.The primary challenge to the stability of organic-inorganic hybrid PSCs arises from the vulnerability of A-site organic cations in their structure.These organic components are susceptible to volatilization or decomposition when exposed to high temperatures,light,water,or oxygen,leading to damage in the perovskite structure and a significant reduction in device performance and lifespan.In contrast,inorganic cesium lead halide perovskites exhibit excellent light and thermal stability by replacing the organic cations with Cs⁺,providing a reliable basis for the long-term operation of the cells.Among the inorganic cesium lead halide perovskites,CsPbI₂Br has emerged as a prominent research focus due to its suitable bandgap and excellent photothermal stability,displaying substantial potential for development.Although CsPbI₂Br has significant advantages in stability,it currently faces two severe challenges:one is the lower device efficiency,which has a substantial gap compared to organic-inorganic hybrid PSCs in terms of PCE,the other is sensitivity to moisture that can induce phase transitions under high humidity conditions,severely impacting long-term device stability.This paper aims to develop effective strategies for enhancing the performance and stability of CsPbI₂Br PSCs through optimization of various functional layers including the perovskite layer,hole transport layer（HTL）,and electrodes.The specific research content is outlined as follows:（1）To achieve high performance while further reducing manufacturing costs of CsPbI₂Br PSCs,we introduced a hydrophobic organic material,4-Chlorobenzoic acid（CBA）,as the anode modification layer and combined it with Ag to construct a CBA/Ag composite electrode.The CBA anode modification layer was prepared using a simple solution spin-coating method,which not only increases the work function of the Ag electrode but also eliminates the need for expensive Au electrodes or Mo O₃/Ag electrodes that require high-temperature vapor deposition methods.Additionally,the hydrophobic CBA layer effectively protects the moisture-sensitive perovskite material by preventing moisture invasion from air.The introduction of CBA also fills micropores in HTL,thereby slowing down migration of free halide ions in the perovskite and corrosion of the electrode,ultimately improving device stability.Consequently,CsPbI₂Br PSCs based on the CBA/Ag composite electrode achieved a PCE of 14.32%along with excellent stability.（2）To mitigate the instability arising from doping agents in the 2,2’,7,7’-tetrakis（N,N-di-p-methoxyphenylamine）-9,9’-spirobifluorene（Spiro-OMe TAD）HTL and the stability issues triggered by residual stress in the perovskite layer,we introduced a p-type organic polymer material,Poly[2,1,3-Benzothiadiazole-4,7-diyl[4,4-bis（2-ethylhexyl）-4H-cyclopentano[2,1-B:3,4-B′]dithiophene-2,6-diyl]]（PCPDTBT）,as the hole transport material,replacing traditional spiro-OMe TAD.Unlike spiro-OMe TAD which requires doping agents and leads to stability concerns due to their presence,PCPDTBT does not require any doping process thereby resolving these stability issues.Additionally,we have employed a thermal spin-coating technique for preparing the HTL which introduces compressive stress above the perovskite layer to counterbalance internal residual tensile stress within it.This approach effectively mitigates problems such as internal defects and halide segregation in the perovskite layer resulting in improved device performance and enhanced stability.Ultimately utilizing PCPDTBT as a hole transport material along with our stress-balancing strategy has enabled us to achieve high PCE of up to 16.4%and exhibit excellent stability in CsPbI₂Br PSCs.（3）To enhance the quality of perovskite thin films,we incorporated 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane（Crypt-222）additive into the CsPbI₂Br perovskite precursor solution.By exploiting the chemical interactions between Crypt-222 and the precursor components Pb²⁺and Cs⁺,we effectively delayed the crystallization process of the perovskite layer,thereby improving its crystalline quality and enhancing both performance and stability of CsPbI₂Br PSCs.Additionally,we proposed a spectral complementarity strategy based on utilizing a CsPbI₂Br perovskite photoactive layer in combination with microcavity spectral selective electrodes to fabricate semitransparent perovskite solar cells（STPSCs）,which can efficiently convert sunlight into electricity while transmitting red light essential for plant photosynthesis.Ultimately,our optimized CsPbI₂Br STPSCs achieved an impressive PCE of 15.32%with only a marginal efficiency loss of 7.54%,along with a peak transmission rate of 46%at 665 nm wavelength;these findings offer valuable insights for developing self-powered greenhouse roof coverings.