Passivation agent with dipole moment for surface modification towards efficient and stable perovskite solar cells

Recently,there has been renewed interest in interface engineering as a means to further push the performance of perovskite solar cells closer to the Schockly-Queisser limit.Herein,for the first time we employ a multi-functional 4-chlorobenzoic acid to produce a self-assembled monolayer on a perovskite surface.With this interlayer we observe passivation of perovskite surface defects and a significant suppression of non-radiative charge recombination.Furthermore,at the surface of the interlayer we observe,charge dipoles which tune the energy level alignment,enabling a larger energetic driving force for hole extraction.The perovskite surface becomes more hydrophilic due to the presence of the interlayer.Consequently,we observe an improvement in open-circuit voltage from 1.08 to 1.16 V,a power conversion efficiency improvement from 18%to 21%and an improved stability under ambient conditions.Our work highlights the potential of SAMs to engineer the photo-electronic properties and stability of perovskite interfaces to achieve high-performance light harvesting devices.

Non-Halogenated Solvent-Processed High-Efficiency Polymer Solar Cells:the Role of Diphenyl Ether in Morphology,Light-Trapping,Transport Properties

There is an urgent need to use green non-halogenated solvents to prepare polymer solar cells(PSCs) for industrialization.It is time-consuming but necessary to find a suitable non-halogenated solvent/additive combination for a given donor:acceptor materials system.In this research,we report a non-halogenated binary solvent system toluene/diphenyl ether(DPE) for the PBDTT-DTffBT:PC_(71)BM and PM6:Y6 blending systems that exhibit comparable power conversion efficiency(PCE) to that of devices prepared with halogenated solvents.The nano scale morphology indicates that blending film processed solely with toluene has poor phase segregation and a rough surface,which hinders charge separation and interfacial contact.Besides,the total absorption spectra revealed significant light-trapping losses in the toluene-processed solar cells,resulting in low photocurrent generation.DPE incorporation addresses these issues and significantly improves the short-circuit current density and fill factor.Moreover,non-halogen solvent-processed devices exhibit high hole mobility and low transporting impedance properties.The present study enriches the families of eco-friendly,high-efficiency PSCs fabricated using nonhalogenated solvents.

Morphology and Performance of Poly（2-methoxy-5-（20-ethyl- h exyloxy）-p-p he nyle n evi nylene） （M E H-PPV）： （6,6）-Phenyl-C61 - butyric Acid Methyl Ester （PCBM） Based Polymer Solar Cells

Polymer solar cells were fabricated based on composite fihns of poly（2-methoxy-5-（2＇-ethyl-hexyloxy）-1,4- phenylenevinylene） （MEH-PPV）：fullerene derivative （6,6）-phenyl-C61-butyric acid methyl ester （PCBM） with weight blend ratio of 1 ： 3, 1 ： 4 and 1 ： 5, spin-coated from chloroform （CF）, chlorobenzene （CB）, and o-dichlorobenzene （ODCB） solutions, respectively. Photoinduced current and power conversion efficiency （PCE） of the devices show a dependence on the solvents. The solar cells have the highest PCE at 1 ： 5 blend ratio. Transmis- sion electron microscopy （TEM） morphology reveals that there are some voids in MEH-PPV：PCBM films. The void number decreases with the solvent from CF to CB and ODCB. We found the voids are located at the bottom of the films through electron tomography technique by TEM and film bottom-side morphology study by atomic force microscopy. The charge carrier transport efficiency and collection efficiency should decrease greatly due to the voids, and the more voids the film has, the more degree the efficiencies decrease. PCE of the solar cell prepared from CF is lower than that of the solar cells prepared from CB and ODCB. The void phenomenon of MEH-PPV：PCBM based solar cell and method to investigate the void position provide an experimental evidence and research mentality to fabricate polymer solar cell with high performance.

Effects of BTA2 as the third component on the charge carrier generation and recombination behavior of PTB7:PC71BM photovoltaic system

Effects of a benzotriazole(BTA)-based small molecule,BTA2,as the third component on the charge carrier generation and recombination behavior of poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]](PTB7):[6,6]-phenyl-C71-butyric acid methyl ester(PC71BM)organic solar cells(OSCs)were investigated by optical simulation of a transfer matrix model(TMM),photo-induced charge extraction by linearly increasing voltage(photo-CELIV)technique,atomic force microscope(AFM),and the Onsager–Braun model analysis.BTA2 is an A_(2)-A_(1)-D-A_(1)-A_(2)-type non-fullerene small molecule with thiazolidine-2,4-dione,BTA,and indacenodithiophene as the terminal acceptor(A_(2)),bridge acceptor(A_(1)),and central donor(D),respectively.The short-circuit current density of the OSCs with BTA2 can be enhanced significantly owing to a complementary absorption spectrum.The optical simulation of TMM shows that the ternary OSCs exhibit higher internal absorption than the traditional binary OSCs without BTA2,resulting in more photogenerated excitons in the ternary OSCs.The photo-CELIV investigation indicates that the ternary OSCs suffer higher charge trap-limited bimolecular recombination than the binary OSCs.AFM images show that BTA2 aggravates the phase separation between the donor and the acceptor,which is disadvantageous to charge carrier transport.The Onsager-Braun model analysis confirms that despite the charge collection efficiency of the ternary OSCs being lower than that of the binary OSCs,the optimized photon absorption and exciton generation processes of the ternary OSCs achieve an increase in photogenerated current and thus improve power conversion efficiency.