Interface Engineering And Optical Management For High-Performance Semitransparent Polymer Solar Cells

Polymer solar cells?PSCs?possess unique properties of low cost,flexible,semitransparent,solution processing,and potential for large-area manufacturing,showing a wide range of research and application value.Remarkable progress in PSCs has been made in recent years with power conversion effciencies?PCEs?reaching 10–14%.Compared with inorganic materials,the absorption spectra of organic materials are discontinuous and variable by changing the chemical structure,making the PSCs in semitransparent appearance in the visible region.On the one hand,semitransparent PSC can be used as the bottom cell in a tandem structure;on the other hand,it can also be applied in buildings,car window,and agricultural greenhouse etc.,and is considered as the most prospective product for market application.However,it is still great challenge for semitransparent PSCs to achieve high PCE yet with good transmittance and color rendering properties,and semitransparent PSCs require specific performance to meet the needs of different applications.In this thesis,we focuse on fabricating high-performance semitransparent PSCs on the basis of the optimazition of the opaque device performance by selecting suitable donor and accepter materials and also with the help of interface engineering and optical simulation,and then exploring the potential applications according to the peculiarity,which can be mainly divided into the following three parts:In chapter 3,we fabricated PSCs using PTB7-Th:PC₇₁BM as the light harvesting layer and PF3N-2TNDI,a thickness-insensitive n-type polymer with enhanced electron transporting capability,as the electron transport layer?ETL?.Optical simulations indicate that PF3N-2TNDI can effectively modulate the optical field and charge generation rate distribution within the active layer,and it will also facilitate to generate addition photocurrent when contacts with the donor and increase the short-circuit current density(J_sc).Therefore,PSCs with optimized PCE of over 9%was achieved when an ultrathin active layer of 50 nm was used.The high PCE based on an ultrathin active layer further triggered us to explore using this device confguration for semitransparent PSCs.The thickness of PF3N-2TNDI film and untrathin silver layer was systematically tuned with the aid of optical modeling,and the PF3N-2TNDI layer promoted the growth of high quality ultrathin silver film as efficient transparent electrode.As a result,a state-of-the-art semitransparent PSC performance with a PCE over 6%together with an average visible transmittance?AVT?of over 30%was achieved.Moreover,these semitransparent PSCs exhibited nice transparency color perception and extraordinary color rendering capacities with color render indexs?CRIs?approaching100%,meeting the critical requirements for using as power-generating windows and paves the way for the application of these semitransparent PSCs for building integrated photovoltaics.In chapter 4,we fabricated ternary nonfullerene PSCs with complementary absorption using the large bandgap polymer J52 as the donor,and the medium bandgap IT-M and low bandgap IEICO as the acceptors,achieving the efficiency over 10%.The addition of the third component IEICO can extend the absorption spectra of the devices to the near infrared region,which is beneficial for enhanced performance of semitransparent PSCs.Optical modeling suggests that single optical layer of Mo O₃ can modulate the optical field within the device,therefore optimizing both the PCE and AVT in semitransparent PSCs.Meanwhile,Mo O₃ can also protect the untrathin silver film electrode,thus improving the stability of the devices.In addition,considering that the human eye is most sensitive to wavelengths at around 550 nm,the transmittance of the devices in this chapter was defined by luminosity in order to satisfy the optical requirements of the human eye vision in practical applications.By optimizing the thickness of the active layer,silver electrode,and Mo O₃ optical layer simultaneously,a superior performance with a PCE of 6.21%together with a luminosity of 29%was achieved for semitransparent PSCs.In chapter 5,taking advantages of the broad and strong absorption of the narrow bandgap nonfullerene acceptor IEICO-4F and high electron mobility of the fullerene acceptor,we constructed J52:IEICO-4F:PC₇₁BM ternary PSCs.The introduction of PC₇₁BM contributed to the suppressed recombination and enhanced charge extraction and transport,all accounted for enhanced the J_sc and fill factor,and higher LUMO energy levels of PC₇₁BM also improved the open circuit voltage,thus,PCE up to 10.68%was achieved for the ternary PSCs.Then,we took one step further to fabricate semitransparent PSCs,and the semitransparent devices show higher transmittance in the range of wavelengths from 400 to500 nm and 600 to 700 nm,matched well with the absorption spectra of the main component of green plants such as chlorophyll,which is prospective for photovoltaic greenhouse.Herein,crop growth factor?G?was selected to define the transmittance of semitransparent devices.By tuning the thickness of silver electrode,an optimized semitransparent PSC performance with a PCE of 7.75%together with crop growth factor of 24.8%was achieved.This study proposes a significant guidance for future applications of semitransparent PSCs in photovoltaic greenhouse.