The Study Of Perovskite Solar Cells And Their Applition In All-perovskite Tandem Solar Cells

In the past few years,organic–inorganic hybrid halide perovskite have attracted enormous attention in many optoelectronic fields,including solar cells,light-emitting diode,photodetector,field effect transistors and semiconductor lasers,because of their excellent photoelectric and electrical properties.Especially in the field of solar cells,it is considered as a prospective class of materials for efficient conversion of solar energy.These typical organic–inorganic hybrid halide perovskites possess excellent properties:high absorption coefficient,low exciton binding energy,high carrier mobility,long carrier diffusion length,ambipolar charge transport capabilities,tunable band gaps and high defects toleration.The maximum power conversion efficiency(PCE)of single-junction perovskite solar cell(PSC)under AM 1.5G illumination,according to Shockley-Queisser(S-Q)detailed balance is more than 30%with the band gap of 1.5 e V.At present,the maximum PCE of single-junction PSC fabricated by the solution method in the laboratory has reached 25.5%,over 75%of its theoretical efficiency.The stacking strategy is a very effective way to break through the S-Q limit value.In order to further improve the PCE of PSCs,combination of PSCs with low band gap(L-E_g)copper indium gallium selenium(CIGS)and silicon(Si)solar cells to fabricate Perovskite/CIGS and Perovskite/Si tandem solar cells have achieved 24.7%and 29.5%PCE,respectively.Although the Perovskite/CIGS,and Perovskite/Si tandem devices have achieved considerable PCE,CIGS contains rare elements,and the preparation process of Si solar cells is accompanied by high energy consumption and high pollution,and the cost of CIGS and Si solar cells is relatively high.Organic-inorganic hybrid halide perovskites with the ABX₃ structure can be largely tuned by changing A,B,or/and X,achieving high-quality photovoltaic materials over a wide range of band gaps(1.2-2.5 e V).So,all-perovskite tandem solar cell can be fabricated with different band gaps PSCs based on low cost solution method.And making the all-perovskite tandem solar cells has great commercial potential.At present,the PCE of double-junction all-perovskite tandem solar cells is 25.6%,which just exceeds the efficiency of single-junction perovskite solar cells.There are two main reasons for the lag in the development of all-perovskite tandem solar cells:(1)the efficiency of L-E_g perovskite solar cells is lower;(2)The fabrication process of tandem devices is complicated and difficult to fabricate.In this paper,by improving the interface between the hole transport layer(HTL)and the L-E_g perovskite,we have obtained high efficiency L-E_g PSCs.This solved the problem of low efficiency of L-E_gPSCs.Then,we constructed a 4-T all-perovskite tandem solar cell by optical ways,and verified the feasibility of using this L-E_g PSC as the bottom sub-cell of the tandem device.Then we found out the wide band gap(W-E_g)PSCs matching the L-E_g PSCs through theoretical calculations,so that the composed all-perovskite tandem solar cell can obtain the highest PCE.The fabrication of tandem device requires an additional transparent electrode.By optimizing magnetron sputtering conditions,ITO transparent electrodes that can be applied on top of perovskite films were obtained.A new technology to fabricate tandem devices using a double-side ITO substrate was developed which can realize the arbitrary transfer among 2-T,3-T,and 4-T all-perovskite tandem devices.Finally,by improving the traditional 4-T tandem device fabrication process,we replaced all the electrodes of the two sub-cells with transparent electrodes to construct a bifacial all-perovskite tandem solar cell.Through the above research,this thesis provides new research ideas and directions for the structure design and fabrication process of all perovskite tandem devices.The specific content is as follows:1.We use diluted PEDOT:PSS as the hole transport material(HTM)to obtain a thinner PEDOT:PSS HTL,improve its conductivity and transmittance.The defect state density between the interface is reduced because of the interface between HTL and perovskite is improved.In turn,the recombination of charge between interfaces is inhibited and the efficiency of charge extraction and transmission is improved.At the same time,we also found that the energy level of thinner PEDOT:PSS matches well with the L-E_g perovskite energy level,which reduces the recombination loss.The short-circuit current(J_SC)and open-circuit voltage(V_OC)have been significantly increased,and the power conversion efficiency(PCE)has been increased from 17.71%to 19.50%,laying the foundation for the preparation of high-efficiency all-perovskite tandem solar cells.2.A 4-T all-perovskite tandem solar cell was fabricated by using an optical splitting system.The two sub-cells work completely independently,and there is no coupling between the two subcells,which make them can be analyzed separately.Calculations indicate that when the spectrum is splitted at 755 nm,PCE of 25.27%for a 4-T all-perovskite tandem solar cell can be obtained when combining a W-E_g sub-cell with PCE of 19.42%and a L-E_g sub-cell with PCE of 19.33%.In fact,we can only separate the spectrum at 720 nm in our lab,thus an efficiency of 23.26%was obtained.This verified the feasibility of using this L-E_g PSC as the bottom sub-cell of the tandem device.3.Theoretical calculations guide us how to match the band gap of two sub-cells to achieve all-perovskite tandem solar cell with the highest PCE.We can practically obtain a low band gap(L-E_g)perovskite with a band gap of 1.21 e V.When combining it with a1.8 e V wide band gap(W-E_g)PSC to form a 4-T all-perovskite tandem solar cell,a PCE of 42%can be deduced by calculation.A PCE of 41%for a 2-T device can be obtained when connected it with a W-E_g perovskite with a band gap of 1.7 e V.4.Next,we used magnetron sputtering ITO to fabricate transparent electrodes under mild conditions(normal temperature,low power).By using such a semi-transparent ITO as the top electrode of a PSC with the structure of Glass/ITO/PEDOT:PSS/MAPb I_3-xCl_x/PCBM/BCP/ITO,the PCE of 15.29%can be obtained as illumination from the glass side.When the light enters the device from the sputtered ITO side,the PCE is only 14.05%mainly due to the optical loss caused by reflection.When 70 nm thick magnesium fluoride(Mg F₂)deposited on the sputtered ITO,the optical loss caused by reflection can be effectively reduced to recover the PCE back to 15.50%.5.We also developed a new technology to fabricate tandem devices using a double side ITO substrate.This technology can realize the arbitrary transfer among 2-T,3-T,and 4-T tandem devices by means of wiring.At the same time it overcomes dissolution by solvent during the fabrication process of 2-T tandem devices.As a 2-T tandem device,we can obtain a larger open circuit voltage(V_OC)of 1.98 V with an efficiency of 21.17%;For a3-T tandem device,we can obtain the maximum short-circuit current(J_SC)of 27.84m A/cm² and PCE of 17.71%;The highest PCE of 21.55%was achieved for 4-T tandem device.6.Finally,by improving the traditional 4-T tandem device manufacturing process,we replaced all the electrodes of the two sub-cells with transparent electrodes to construct a bifacial all-perovskite tandem solar cell.This device structure is self-package by utilizing the substrates of the two sub-cells as the packaging glass.The reflected light entering from the bottom can be used to obtain additional PCE because of the bottom electrode is also a transparent electrode.By using a plane mirror the reflected light intensity reaches50%of AM 1.5G illumination,an additional 8.05%PCE is obtained,and thefinal PCE can reach 29.47%.A rough estimation shows that sufficient buoyancy to float the device on the water can be generated when a distance about 3 mm is kept between the two sub-cells during packaging.Such a design has its potential competition in the field of water photovoltaic construction.