| Photovoltaic technology offers great opportunities to meet growing global energy needs in a sustainable and environmentally friendly manner.In recent years,organic-inorganic halide perovskite solar cells have attracted great attention because of their direct band gap,broad light absorption,low exciton binding energy,long carrier lifetime,as well as low cost and easy preparation.At the same time,after more than 10 years of research,the development of perovskite solar cells has also reached a milestone,consist of the breakthroughs in the power conversion efficiency,the improvement of device stability,the preparation of large-area modularization,and the diversified applications of flexible wearable and translucent cells.Among them,the power conversion efficiency of perovskite solar cells has made a great breakthrough,rising sharply from 3.8% to 25.2% in the past decade,which is comparable to commercial standard silicon-based cells.However,the preparation cost and stability of perovskite solar cells are still the bottleneck restricting their further development and application.On the premise of achieving higher power conversion efficiency,how to reduce the preparation cost and improve the stability of the device in a variety of environments has become a hot issue in this field.As a critical component of perovskite solar cells,the hole transport layers play an essential role in optimizing the power conversion efficiency and long-term stability of the device.At present,most of the efficient perovskite solar cells use doped organic Spiro-OMe TAD as hole transport material,which has a negative impact on the cost control of the device and the long-term stability of the device performance.Accordingly,searching for a low-cost,efficient and stable hole-transporting material in perovskite solar cells is still one of the hottest research subject in this field.Herein,(Cu2SnS3)x(ZnS)1-x quantum dots were developed by us,which were as new inorganic hole transport materials in perovskite solar cells,and carried out the following work around(Cu2SnS3)x(ZnS)1-x quantum dot:Part I: Firstly,Cu2SnS3 quantum dots with low cost,high yield and uniform morphology were prepared by simple thermal injection method,and used as hole transport material in perovskite solar cells with an architecture of ITO/Sn O2/(FAPb I3)1-x(MAPb Br3)x/Cu2SnS3/Au.A remarkable power conversion efficiency of 16.4% was acquired in the Cu2SnS3-based perovskite solar cell by optimizing the precursorsolution concentration,spinning speed and annealing temperature in the process of hole transport material spin coating.The hole extraction ability,carrier transport,recombination process and device stability of the Cu2SnS3 and Spiro-OMe TAD-based perovskite solar cell in the same devices were analyzed and compared.It is found that,compared with Spiro-OMe TAD hole transport layer reference,the Cu2SnS3 quantum dot hole transport layer has better hole extraction capacity and humidity stability.The results show that Cu2SnS3 quantum dots as a low-cost,efficient and stable hole transport layer can effectively reduce the cost of the device and provide effective protection for the degradation of perovskite layer.Part II: On the basis of the above,the band gap of Cu2SnS3 quantum dots was adjusted by alloying with larger bandgap ZnS.In order to understand the effect of different alloy ratios on the performance of perovskite solar cells,the(Cu2SnS3)x(ZnS)1-x quantum dots with different ratios were synthesized and used as hole transport materials for perovskite solar cells.The conclusions are as follows:with the addition of ZnS,the power conversion efficiency of perovskite solar cells increases at first and then decreases.The optimal power conversion efficiency of perovskite solar cells is obtained when using(Cu2SnS3)0.7(ZnS)0.3 as the hole transport layer.And compared with the photovoltaic parameters based on Cu2SnS3 devices(filling factor: 0.71,open circuit voltage: 0.96 V,power conversion efficiency 16.4%),(Cu2SnS3)0.7(ZnS)0.3-based perovskite solar cells showed relatively higher filling factor(0.74)and open circuit voltage(1.02 V),thus achieving higher power conversion efficiency(17.44%).Further characterization and analysis show that the improvement of filling factor and open-circuit voltage is mainly attributed to the following factors,firstly,(Cu2SnS3)0.7(ZnS)0.3 quantum dots have higher conductivity and hole extraction ability,so that the photogenerated holes in the perovskite absorption layer can be extracted and transmitted quickly,thus higher open-circuit voltage and filling factor can be obtained.In addition,the larger charge recombination resistance and smaller hole transport resistance at the interface of the device based on(Cu2SnS3)0.7(ZnS)0.3 quantum dots also contribute to the hole transport at the interface,thus increasing the open-circuit voltage and filling factor of the device. |
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