Application Of Dopant-free Hole Transport Materials In Perovskite Solar Cells

Organic-inorganic hybrid perovskite solar cells are widely concerned by researchers due to their excellent photoelectric conversion performance.Within ten years,their certified power conversion efficiency(PCE)has increased from 3.8% to 25.2%,and the development speed is amazing.The excellent performance is due to the broad spectrum absorption,high carrier mobility and diffusion length of the perovskite light-absorbing layer.Although perovskite solar cells are promising photovoltaic devices in the third generation of solar cells,the road to industrialization still has a long way to go.First of all,perovskite materials are sensitive to water and light,and their stability cannot meet the requirements.Secondly,commonly used hole-transporting materials are expensive,and precious metals as counter electrodes also increase the manufacturing cost.PEDOT is a cheap and easily available polymer material with high conductivity.Because it is difficult to dissolve in conventional organic solvents,it is mostly used in p-i-n perovskite solar cells.In this paper,by changing the length of the alkyl side chain,three PEDOT derivatives P6,P10 and P14 were developed as doped-free hole transport materials,which can be applied to the formal structure of perovskite solar cells by solution spin-coating method.We systematically studied the effect of alkyl side chain length on the film morphology and the overall performance of solar cells.After weighing the trade-off effect between the high hole mobility generated by the stronger intermolecular interaction and the high solubility and excellent film-forming ability generated by the increase in alkyl chain length,the optimized P10-based perovskite solar cell achieved a PCE of 16.2%.The significant improvement of its photovoltaic performance are mainly due to the combined effect of uniform film formation and effective hole transport capability.In addition,the P10-based device exhibited surprising longterm stability under a relative humidity of 80% environmental conditions.Through the analysis of various types of organic small molecule materials,we synthesized a small molecule DOC1 with a "D-A" structure.This material has a simple molecular structure and a high hole mobility.The rigid structure of the diphenyl ring helps intermolecular π-π stacking which is conducive to the conduction of electric charge in the vertical direction.The excellent properties make it suitable for use as a doped-free hole transport material in n-i-p perovskite solar cells.After assembling the device,a PCE of 16.4% was achieved under standard sunlight.The reduced application cost of the non-doped process also simplifies the preparation process and provides a new idea for the subsequent synthesis of low-cost hole transport materials.