Regulation Of The Solution And Device Performance In The Active Layer And Interface Layer Of Organic Photovoltaic Cells

As one of the clean renewable energy technologies,organic photovoltaic(OPV)cells have attracted extensive research interests owing to their unique potentials of lightweight,flexibility,transparency and easy large-scale fabrication by low-cost solution processing methods.The design and development of precursor solution for high-performance organic photovoltaic materials functional layer play a prominent role in promoting the OPV cells performance,which is also regarded as one of research hotspot in this filed.For better understanding of the structure-performance relationship and thus achieving high power conversion efficiency(PCE)and controllable morphology for device fabrication technology,we in-depth studied the precursors solution of functional layer of high-performance organic photovoltaic cells,which could provide useful guidances for developing the large-area commercial production of high-performance OPV cells by printing.The main content of this dissertation is divided into the following three parts:1.Molecular ordering,mesoscale morphology and charge recombination were systematically studied the in thick-film non-fullerene OPV cells based on a high-performance PBDB-T:IT-M system.We found that thermal annealing can be very useful method to boost the performance of thick-film PBDB-T:IT-M devices.Based on this treatment method,the prepared PBDB-T:IT-M non-fullerene OPV cells can provide an energy conversion efficiency of up to 9.4%at an active layer thickness of 250 nm.In addition,when the active layer thickness of the device is 400nm,the high efficiency of the device can still maintain close to 9%.UV-vis absorption,SCLC mobility,and morphology studies show that the electron mobility of IT-M becomes higher and the blend films possess more ordered packing and a higher average domain purity after thermal annealing.Consequently,these factors improve charge creation and transport,and thus lead to an improved thickness insensitivity of device performance.This work highlights the importance of controlling molecular ordering and phase separation in achieving high-efficiency thick-film non-fullerene OPV devices,which will be beneficial for commercial roll-to-roll printing technology.2.Three different acceptors(IT-4C1-C6,IT-4C1-C8 and IT-4C1-C10)were designed and synthesized to investigate the influence of alkyl side chain length on device performance.We fabricated the photovoltaic devices with the studied bulk heterojunction(BHJ)layers,exhibiting PCE from 6.67%to 13.54%.In order to obtain the ideal morphology,we made an intensive study on the structure and aggregation relationship of the acceptor with different alkyl side chain length.By reasonable tuning the alkyl side chain length of the acceptor,acceptor materials effectively balanced the aggregation behaviour and particularly achieved good miscibility with conjugated donor polymers in BHJ active layer.As the lengths of alkyl pendant getting longer from IT-4C1-C6 to IT-4C1-C8 and to IT-4C1-C10,the non-radiative and radiative recombination can be effectively depressed,leading to the improved photovoltaic performance.3.An easy method was introduced to the sol gel control of ZnO precursor for high performance ZnO cathode interfacial layer(CIL)in inverted OPV cells.Based on detail study about the composition-structure-activity relationship,we proposed an effective strategy of tracing the balance between cluster size and composition by changing the amines with different pKbs.We addressed the reasonable pKb-dependence of cluster size and composition,as well as the causality between dispersion properties and rheological behaviors based on spectrum and scattering studies.With further treatments on the precursors,great differences in photovoltaic performances were resolved in the devices with various blade coated ZnO CILs.An approaching 18%PCE was achieved in the inverted OPV cells with ZnO CIL fabricated from the best precursor.Encouraged by the higher stability and hence the attractive operation significance,it is important to implement sophisticated methodological modifications on the synthesis or preparation of ZnO layer since it is the only CIL available to the current state of the art in inverted OPV cells.