Polymer Tandem Solar Cells

This thesis aims at exploring methods and mechanisms to enhance the efficiency of polymer tandem solar cells.Firstly,the solution-processed component interfacial buffer layers of the interconnecting layers in tandem solar cells are inveatageted.Secondly,component distribution in the blend active layer are investageted to design single solar cells structure,which further helps to design and prepare the final structure of tandem solar cells.The main contents of this thesis include four aspects:1)Zirconium isopropoxide(Zr[OCH(CH3)2]4,ZrIPO)is a cathode modified layer,which can be prepared by simply spin-coating a solution of ZrIPO onto the photosensitive layer at room temperature without any other post-treatment.ZrIPO is interposed between the A1 cathode and the active layer as a cathode modification layer in conventional polymer solar cells.When ZrIPO/Al is utilized as the cathode in a polymer solar cell instead of the traditional Ca/Al cathode,the short-circuit current can be significantly improved,and the series resistance is also reduced synchronously.When the ZrIPO/Al cathode is used in polymer solar cell with P3HT:PC60BM as active layer,the photoelectric conversion efficiency measured under standard illumination conditions(AM 1.5G,100 mW/cm2)is 4.47%,which is significantly higher than 3.69%of photoelectric conversion efficiency from solar cells with Ca/Al cathode under the same conditions.When solar cells adopting PBDTBDD:PC60BM as active layer and ZrIPO/A1 as cathode electrode,the photoelectric conversion efficiency of up to 8.07%can be achieved.These results indicate that ZrIPO is a promising electron transport layer material for realizing high-performance polymer solar cells in place of traditional low-function alkaline earth metals.2)Solution-processable titanium(diisopropoxide)bis(2,4-pentanedionate)(TIPD)material is employed as a cathode buffer layer in inverted nonfullerene based single polymer solar cell.The inverted single junction solar cells are prepared based on the electron donor and electron acceptor which can form complementary absorption.Surface potential,morphology,water contact angle,time-of flight secondary ion mass spectrometry of blend active film in polymer solar cells are investigated to explore the mechanism and method to improve the power conversion efficiency;In addition,the employment of the inverted structure with high-work function metal as an anode,avoiding the moisture and oxygen sensitive Ca/Al cathode electrode,effectively improves the long stability of polymer solar cells.In PBDTBDD:ITIC-M blend film,PBDTBDD mainly distribute in the top side,while ITIC-M dominates the bottom of the film,which is suitable in solar cells with inverted structure.Inverted solar cells with TIPD and conventional solar cells based on PEDOT:PSS have been prepared,the results show that the inverted solar cells has achieved a power conversion efficiency of 11.69%,which is 20.89%higher than 9.67%of conventional solar cells.Also,the inverted structure device avoids the vapor and oxygen sensitive Ca/Al electrode,which is benefit to the stability of solar cell3)Based on the tentative findings related to electron transport layer and photoactive layer,we further apply it in inverted tandem solar cells.In order to simplify the optimization steps,the same active layer PTB7-Th:PC71BM are used in both front and rear sub-cells.Through exploring the feasibility of TIPD used as both the cathode modification layer and the electron extract layer of interconnecting layer,the effect of tandem structure on the improvement of photoelectric conversion efficiency is explicated.Inverted tandem solar cells are manufactured and it is found that the photoelectric conversion efficiency of the prepared tandem solar cells increased to 8.11%compared with single junction solar cells.And the open circuit voltage of tandem solar cells fulfilled the summation of the two open circuit voltage of the two component subcells.4)In order to improve the photoelectric conversion efficiency of polymer solar cells through making full use of the incident photons,we have designed and fabricated tandem polymer solar cells using photoactive layers with different absorption spectrum ranges.As the fullerene acceptors are endowed with strong absorption in short wavelength region,and some certain nonfullerene acceptors are endowed with wide absorption extended to nearly 1000 nm.Based on both fullerene and nonfullerene acceptors,inverted tandem solar cells are designed and manufacted with complementary absorption to achieve the enhancement in power conversion efficiency.Tandem solar cells with structure of ITO/TIPD/PBDTBDD:PC71BM/MoO3/Ag/PFN-Br/PTB7-Th:IEICO-4F/MoO3/Al have been prepared.And the tandem tandem solar cells can achieve a photoelectric conversion efficiency of 9.74%and an open-circuit voltage of 1.503V equal to the summation of both front single cell and rear single solar.And the results also show that the insertion of ultra-thin Ag between ITO and PFN-Br can improve the fill factor of inverted single-junction devices.This will help deepen the understanding of the physical mechanism of the interconnecting electrode of the polymer tandem solar cell,and will help to deeply understand the interface characteristics of subcell and the material of interconnecting electrode,and help to deeply understand the interconnecting electrode.The relationship between the characteristics of the interface layer and the photovoltaic performance of the device also lays a solid foundation for further improving the performance of the polymer solar cell.