Research On High-Performance Perovskite Photodetectors And Solar Cells

In recent years,halide perovskite materials have attracted much attention due to their excellent physical properties,such as high carrier mobility,high light absorption capacity,and high defect tolerance,and have become one of the most popular research fields.The fabricated optoelectronic devices also exhibit very excellent performance.Nowadays,the detection sensitivity of perovskite photodetectors(PPDs)ranging from near infrared-visible light-ultraviolet to high-energy rays is continuously increasing.The power conversion efficiency(PCE)of perovskite solar cells(PSCs)has also improved much,and device stability has also made considerable progress.These pioneer works have laid a good foundation for the perovskite materials and devices in future applications.However,in terms of photodetectors,the device performance needs to be further boosted,and reliability and long-term stability are also two points which should be draw attention.In terms of solar cells,long-term stability is currently the most important issue,which is now considered as a systematic project.Based on perovskite materials,this paper carried out research works in the direction of PPDs and PSCs.First,we adopted semiconductor heterojunctions to design and fabricate hybrid PPDs with high overall performance.Then,efficient and stable PSCs were fabricated by using CsF-doped perovskite films.Finally,a layer of phenylbutyl ammonium iodide(PBABr)was spin-coated on the surface of(FAMACs)Pb(I1-xBrx)3(MA+:CH3NH3+,FA+:CH(NH2)2+)film to passivate surface defects,and PSCs with both high PCE and open-circuit voltage(Voc)were obtained.The main works and innovations are listed as following:1.photodetector fabricated by a single-layer perovskite thin film(MAPbI3)suffer serious recombination of photo-generated carriers,so the photocurrent of the device is very low.Although the use of two-dimensional materials with high electrical conductivity can obtain a large optical gain,the dark current will also increase greatly.There are some challenges to realize photodetectors with high overall performance.Here we comparatively studied the single MAPbI3 photodetector and TiO2 nanocrystals/MAPbI3 photodetector in which TiO2 nanocrystals layer is as the charge transport layer,and found that the latter exhibited effectively suppressed dark current due to the formation of space charge regions.Under the light,the perovskite layer absorbs light,and the TiO2 nanocrystals layer transports photo-generated carriers.Due to the spatial separation of photo-generated carriers,the photocurrent of the photodetector is greatly improved while maintaining relatively low dark current.The bilayer device achieved a responsivity of 0.12 A W-1,an on/off ratio of>4×103,and a detectivity of 1.85×1012 Jones.In order to further improve the responsivity,a single-crystal Si material with high mobility was used as the charge transport layer.In order to reduce the dark current,a thin layer of TiO2 nanocrystals was spin-coated in the middle to adjust the interface barrier.The Si/TiO2 nanocrystal s/MAPbI3 hybrid photodetector achieved a responsivity of 62.5 A W-1,an on/off ratio of>6×103,and a detectivity of 4.85×1013 Jones.Because Si participates in absorbing near-infrared light,the device's cut-off wavelength of spectral response extends to 1100 nm.2.Cs doping has been widely used to obtain high-quality mixed perovskite films((FAMACs)Pb(I1-xBrx)3).The one-step method is usually adopted.In comparison,the two-step method can easily control the film formation process and is compatible with large-area fabrication processes.However,in the two-step method,it is difficult to incorporate Cs into perovskite film.In this work,we used CsF as the Cs source for the first time,first obtained the CsF-modified PbI2 seed,and then obtained a high-quality(FAMACs)Pb(I1-xBrx)3 film.Compared with the control film,the crystalline quality of the Cs-doped film was greatly enhanced,showing better uniform and monolithic surface morphology,and its PL carrier lifetime increased from 686 ns to 1413 ns.The Cs-doped film showed better stability in tests of temperature(1 hour at 120?)and humidity(1 hour at 80%humidity).Cs-doped PSCs obtained an Voc of 1.145 V,a short-circuit current(Jsc)of 24.55 mA cm-2,a fill factor(FF)of 75.02%,and a PCE of 21.09%;the device kept 96%of its initial PCE after being heated at 60? for 300 hours and remained 95%of its initial PCE after being stored in air for 180 days.3.Surface passivation which has been widely studied in recent years is an effective method to further reduce the Voc loss of PSCs and thus improve PCE.However,it is hard to achieve high Voc(>1.2 V)and PCE(>22%)simultaneously for a well-passivated PSCs.In this work,we used PBABr film to passivate the surface of(FAMACs)Pb(I1-xBrx)3 film to reduce surface defects and suppress non-radiative recombination.After PBABr treatment,the PL carrier lifetime of(FAMACs)Pb(I1-xBrx)3 film increased from 1231 ns to 2475 ns.The champion PSC with surface passivation achieved an Voc of 1.216 V,a Jsc of 24.69 mA cm-2,a FF of 75.52%,and a PCE of 22.67%,and the corresponding Voc loss was only 344 mV.The passivation effects of a series of phenalkylammonium halide salts on the surface of(FAMACs)Pb(I1-xBrx)3 films were compared.It was found that longer alkyl chain was beneficial to enhance the passivation effect,and the Br salts showed better passivation effect than the I salts.