Studies On Performance Of Polymer And Perovskite Solar Cells

Solar cell is one of the best ways to take advantage of solar radiation.Polymer solar cells and perovskite solar cells have achieved rapid improvement in efficiency.The development of polymer solar cells is benefiting from the synthesis of novel donor/acceptor materials,modification of interface layers and engineering of solvent/thermal annealing.The high performance of perovskite solar cells is attributed to the superior properties of the perovskite materials:high optical absorption coefficient,high carrier mobility and long carrier diffusion distance and bipolar charge transport.However,there are still many scientific problems to be solved,such as the improvement of the efficiency of polymer solar cells and the reduction of materials cost;the improvement of the current-voltage hysteresis behavior,repeatability and stability of perovskite devices.Therefore,this dissertation is dedicated to solving current scientific issues,focusing on the synthesis and modification of inorganic oxides as interface layers for polymer solar cells,optimization of halogen-regulated perovskite film morphology and crystal growth,and the treatment of perovskites with polymer and doping to improve the power conversion efficiency,repeatability and stability of the devices.In chapter ?,the enhanced efficiency of the inverted polymer solar cells by using a conjugated polyelectrolyte to reengineer the surface of sol–gel processed ZnO is reported.It is found that nearly 22%enhancement in efficiency is observed from the inverted polymer solar cells with ZnO reengineered by conjugated polyelectrolyte,as compared with the inverted polymer solar cells with ZnO.The enhanced efficiency is originated from reduced surface roughness and decreased relative work function of ZnO thin layer modified by conjugated polyelectrolyte.In chapter ?,we report solution-processed vanadium oxide?s-VOx?thin film as the hole extraction layer for polymer solar cells.A s-VOx thin film is prepared simply by the spin-coating of ammonium metavanadate ammonal water solution on the surface of indium tin oxide coated glass substrates,followed by thermal annealing at 210?for 5 minutes in air.The scanning Kelvin probe measurement indicates that the relative work function of the s-VOx film is-5.3 eV,which allows the conjugated polymer PTB7 to form an Ohmic contact with the s-VOx,resulting in a high open-circuit voltage for polymer solar cells.It is found that polymer solar cells incorporated with the s-VOx possess a comparable power conversion efficiency but better shelf-stability than that of devices incorporated with the poly?3,4-ethylenedioxythiophene?:poly-?styrenesulfonate?hole extraction layer.In chapter ?,we study the effect of PC₆₁BM dissolved in the chlorobenzene and pyridine blend solvent(PC₆₁BM-Py)as the electron extraction layer on the performance of the perovskite solar cells.The results show that the PC₆₁BM-Py thin film has a higher conductivity and a smoother and denser film surface than the PC₆₁BM thin film.In addition,the measurements of transient photocurrent and transient photovoltage indicate that the device with PC₆₁BM-Py exhibits longer charge carrier lifetime and shorter carrier extraction time,indicating that it has less charge carrier recombination.As a result,more than 21.6%enhanced efficiency is observed for the device with PC₆₁BM-Py.In chapter ?,the effect of the molar ratio of Br:I in CH₃NH₃Pb(I_1-xBr_x)₃ on device performance is investigated.The molar ratio of Br:I in CH₃NH₃Pb(I_1-xBr_x)₃ is adjusted from Br:I=0:1 to Br:I=1:0,and when the molar ratio of Br:I is 0.15:0.85,the corresponding inverted planar heterojunction perovskite solar cells exhibit a maximum efficiency of 18.74%with the average efficiency of 17.96%.In addition,the hysteresis behavior of device has been improved.The improvement in device performance is mainly due to the improvement in the quality of perovskite films with this molar ratio.In chapter?,high-electron-mobility inorganic ternary oxide Zn₂SnO₄ nanoparticles is mixed with CH₃NH₃Pb(I_0.85Br_0.15)₃ as the photoactive layer of perovskite solar cells is investigated.It is found that the electron mobility of the CH₃NH₃Pb(I_0.85Br_0.15)₃:Zn₂SnO₄ thin film is significantly increased.Furthermore,the formation of defect-free perovskite films is promoted by the aggregation of Zn₂SnO₄ nanoparticles at the perovskite grain boundaries and the filling of defects.Compared to the energy level alignment of devices without Zn₂SnO₄nanoparticles doped,the energy level alignment of perovskite solar cell is further matched well because the conduction band of the Zn₂SnO₄ nanoparticles is located at position between the lowest unoccupied molecular orbital of the CH₃NH₃Pb(I_0.85Br_0.15)₃ and the acceptor PC₆₁BM,reducing the energy loss,plus the deep valence band of Zn₂SnO₄ nanoparticles,the hole is transported to the PC₆₁BM from CH₃NH₃Pb(I_0.85Br_0.15)₃ is effectively blocked.By further adjusting the concentration of Zn₂SnO₄ nanoparticles into CH₃NH₃Pb(I_0.85Br_0.15)₃,a reproducibly effective planar inverted perovskite solar cell with an optimal PCE of 21.07%is achieved.In chapter ?,polymer as a template for inducing heterogeneous nucleation of perovskite grains and passivating the defects at the surface of perovskite thin film is investigated.It is found that perovskite thin film treated by polymer possesses smooth surface,large grain size and reduced defect density.Further investigations indicate that such superior features are attributed to the formation of Lewis adduct via the reaction of the unbonded Pb?Lewis acid?in the perovskite and C=O?Lewis base?in the polymer.As a result,a power conversion efficiency was boosted from from 18.80%,which is from pristine perovskite thin film,to 21.05%.In addition,the storage stability and the performance stability of perovskite solar cells under continuous light are enhanced.