Metal oxide vs organic semiconductor charge extraction layers for halide perovskite indoor photovoltaics

Funding: L.K.J. acknowledges funding from UKRI-FLF through MR/T022094/1 and would like to acknowledge (EPSRC): EP/T023449/1. T.K. acknowledges support from the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division under contract no. DE-AC02-05-CH11231 (D2S2 program KCD2S2).Halide perovskite indoor photovoltaics (PVs) are highly promising to autonomously power the billions of microelectronic sensors in the emerging and disruptive technology of the Internet of Things (IoT). However, how the wide range of different types of hole extraction layers (HELs) impacts the indoor light harvesting of perovskite solar cells is still elusive, which hinders the material selection and industrial‐scale fabrication of indoor perovskite photovoltaics. In the present study, new insights are provided regarding the judicial selection of HELs at the buried interface of halide perovskite indoor photovoltaics. This study unravels the detrimental and severe light‐soaking effect of metal oxide transport layer‐based PV devices under the indoor lighting effect for the first time, which then necessitates the interface passivation/engineering for their reliant performance. This is not a stringent criterion under 1 sun illumination. By systematically investigating the charge carrier dynamics and sequence of measurements from dark, light‐soaked, interlayer‐passivated device, the bulk and interface defects are decoupled and reveal the gradual defect passivation from shallow to deep level traps. Thus, the present study puts forward a useful design strategy to overcome the deleterious effect of metal oxide HELs and employ them in halide perovskite indoor PVs.Peer reviewe

Effect of Na and the back contact on Cu2Zn(Sn,Ge)Se4 thin-film solar cells : towards semi-transparent solar cells

Cu2ZnSn1-xGexSe4 (CZTGSe) thin films have been grown onto Mo/SLG and Mo/V2O5/FTO/SLG substrates using thermal co-evaporation followed by a subsequent thermal annealing. A NaF precursor layer was evaporated prior to the deposition of the kesterite absorber layer. In the samples grown on Mo/SLG, it has been found that Na promotes Ge incorporation into the Cu2ZnSnSe4 lattice. The high concentration of incorporated Ge leads to the segregation of Sn-Se secondar y phases as we l l as to an accumulation of Sn next to the Mo layer. The use of 12 and 16 nm NaF thick precursor layers prior to the CZTGSe deposition leads to absorber band gaps of 1.30 and 1.34 eV, and to device performances of 4.7 and 4.0%, respectively. A higher Na content, furthermore, caused the formation of bigger grains, a higher charge carrier concentration and a shorter depletion width. A 12 nm NaF precursor layer was used for the devices grown on FTO-based substrates, producing an optimal back contact that allows achieving efficiencies of 5.6% and transmittance of 30% in the near infrared range. This enhanced performance can be associated with the absence of secondary phases and Ge distribution through the absorber layer. The formation of a MoSe2 layer at the back interface in al l the investigated devices seems to play a crucial role to improve the solar cell efficiency

Wide band gap Cu2ZnGe(S,Se)4 thin films and solar cells: influence of Na content and incorporation method

The influence of the Na content and incorporation procedure into Cu2ZnGe(S,Se)4 (CZGSSe) thin films and solar cells is investigated. The effects of the presence/absence of Se during the deposition of a 15 nm thick NaF layer before and/or after the Cu2ZnGeSe4 (CZGSe) co-evaporation, are compared. Both the Na content, and Na-supply method significantly influence the incorporation of S into the CZGSe lattice and its distribution in the absorber. A [S]/([S] + [Se])-gradient throughout the CZGSSe layers is observed for all the samples and correlated with effects induced by the Na incorporation procedure. For instance, the evaporation of Se together with NaF leads to an increased S concentration in the surface-region of the CZGSSe layer and a modified surface morphology. CZGSSe-based solar cells with band gap energies of about 2 eV are obtained, regardless of the NaF addition method used, while the absence of the NaF layer reduces the S incorporation and the Eg. However, the evaporation of Se together with NaF results in higher Eg and open circuit voltage VOC, probably related to a higher S accumulation near the surface, demonstrating the importance of the [S]/([S] + [Se]) distribution. CZGSSe-based photovoltaic devices with efficiency of 3.2 % and Eg of 2 eV are obtainedThis work was supported by Spanish Ministry of Science, Innovation and Universities Project (WINCOST: ENE2016-80788-C5-2-R), CELL2-WIN: PID2019-104372RB-C32) and European Project INFINITE-CELL (H2020-MSCA-RISE-2017-777968). The authors acknowledge the service from the MiNa Laboratory at IMN-CSIC, and funding from CM (project S2018/ NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E-1794) and European Union (FEDER, FSE

Evaluation of recombination losses in thin film solar cells using an LED sun simulator − the effect of RbF post-deposition on CIGS solar cells

Distinguishing among different electrical loss mechanisms − such as interface and bulk recombination − is a common problem in thin film solar cells. In this work, we report a J–V measurement technique using different illuminating spectra to distinguish between these two recombination losses. The basic idea is to change the relative contribution of bulk recombination to the total losses of photo-generated charge carriers by generating them in different depths within the absorber layer using different spectral regions of the illuminating light. The use of modern LED sun-simulators allows an almost free design of illumination spectra at intensities close to 1 sun. The comparison of two simple J–V measurements, one recorded with illumination near the absorber's band-gap energy and one with light of higher energy, in combination with supporting measurements of the absorber properties, as well as device modeling, enables the extraction of the diffusion length and the interface recombination velocity. Using this technique, we show that in CIGS solar cells, an RbF post-deposition treatment does not only reduce interface recombination losses, as often reported, but also reduces bulk recombination in the CIGS absorber. Furthermore, we find that both cells, with and without RbF treatment, are dominantly affected by interface recombination losses

Evaluation of recombination losses in thin film solar cells using an LED sun simulator − the effect of RbF post-deposition on CIGS solar cells

Distinguishing among different electrical loss mechanisms − such as interface and bulk recombination − is a common problem in thin film solar cells. In this work, we report a J–V measurement technique using different illuminating spectra to distinguish between these two recombination losses. The basic idea is to change the relative contribution of bulk recombination to the total losses of photo-generated charge carriers by generating them in different depths within the absorber layer using different spectral regions of the illuminating light. The use of modern LED sun-simulators allows an almost free design of illumination spectra at intensities close to 1 sun. The comparison of two simple J–V measurements, one recorded with illumination near the absorber's band-gap energy and one with light of higher energy, in combination with supporting measurements of the absorber properties, as well as device modeling, enables the extraction of the diffusion length and the interface recombination velocity. Using this technique, we show that in CIGS solar cells, an RbF post-deposition treatment does not only reduce interface recombination losses, as often reported, but also reduces bulk recombination in the CIGS absorber. Furthermore, we find that both cells, with and without RbF treatment, are dominantly affected by interface recombination losses

The effect of annealing temperature on Cu2ZnGeSe4 thin films and solar cells grown on transparent substrates

9 pags., 7 figs., 2 tabs.Semi-transparent solar cells are the next step for photovoltaics into our daily life. Over the last years, kesterite-type material has attracted a special attention to be used as an absorber in thin-film solar cells because of its low toxicity and earth abundant constituents. Here, Cu2ZnGeSe4 (CZGSe) thin films are grown by co-evaporation and subsequent annealing at a maximum temperature of 480 ◦C or 525 ◦C onto Mo/V2O5/FTO/glass stacks. The goal of this work is to investigate the influence of the annealing temperature on the composition, morphology, vibrational properties, and transmittance of CZGSe layers, the formation of secondary phases, and distribution of elements within the absorber layer as well as on the optoelectronic properties of the corresponding solar cell devices. Raising the annealing temperature to 525 ◦C leads to a more uniform distribution of Cu, Zn, Ge and Se throughout the absorber layer, a reduction of the presence of the GeSe2 secondary phase, which is mainly detected at 480 ◦C, a larger grain size and the formation of a thicker MoSe2 layer at the CZGSe/back contact interface. The strategy of increasing the annealing temperature allows for improved J–V characteristics and higher spectral response resulting in an enhanced device performance of 5.3% compared to 4.2% when using 525 ◦C and 480 ◦C, respectively. Both absorber layers present an optical band gap energy of 1.47 eV. Furthermore, higher annealing temperature has beneficial effect to the CZGSe-based devices without losses in total transmitted light because of the higher diffuse transmittance. This work shows first promising semi-transparent CZGSe-based solar cells possibly open up new routes of applications.This work was supported by Spanish Ministry of Science, Innovation and Universities Project WINCOST (ENE2016-80788-C5-2-R), Project RTI (2018-096498-B-I00, AEI/MICINN/ERDF) and European Project INFINITE CELL (H2020-MSCA-RISE-2017-777968). Authors from IREC belong to the SEMS (Solar EnergyMaterials and Systems) Consolidated Research Group of the ‘Generalitat de Catalunya’ (Ref 2017 SGR 862).MG and MP acknowledge the financial support from Spanish Ministry of Science, Innovation and Universities within the Juan de la Cierva (IJC2018-038199-I) and Ramón y Cajal (RYC-2017-23758) Fellowships respectively. MGP also acknowledges funding from AEI/MICINN (PTA2019-016763-I). The authors acknowledge the service from the MiNa Laboratory at IMN-CSIC, and funding from CM (project S2018/NMT-4291 TEC2SPACE), MINECO (project CSIC13-4E-1794) and European Union (FEDER, FSE).Peer reviewe

19.31% binary organic solar cell and low non-radiative recombination enabled by non-monotonic intermediate state transition

Non-radiative recombination loss suppression is critical for boosting performance of organic solar cells. Here, the authors regulate self-organization of bulk-heterojunction in a non-monotonic manner, and achieve device efficiency over 19% with low non-radiative recombination loss down to 0.168 eV

Semitransparent Wide Bandgap Cu2ZnGe(S,Se)4Thin-FilmSolar Cells: Role of the Sulfurization Process

9 pags., 6 figs., 2 tabs.Semitransparent solar cells are very attractive due to the increasing integration in daily life. Kesterite-type based thin-film solar cells stand out because of its environmentally benign composition and outstanding stability. Herein, the influence of the back contact (Mo/V2O5/FTO or Mo/FTO) and thickness of Cu2ZnGe(S,Se)4 (CZGSSe) absorber layer, grown by sulfurization of coevaporated CZGSe, is investigated. To increase the transparency, thinner absorber layers with higher bandgap energy are produced. A double sulfur gradient through the CZGSSe layer with a considerable S content near the back contact and the formation of Mo(S,Se)2 phase at the back interface is detected for an absorber of only 400 nm thickness. Efficiencies of 3.1% and 2.7% are achieved for 1.2 μm CZGSSe-based devices with Eg of 1.73 and 1.86 eV, respectively, while enabling transmittance values higher than 20% in the near-infrared (NIR). The highest transmittance, 40% in the NIR, is achieved for the 400 nm CZGSSe-based solar cells with Eg of 2.1 eV; however, a significant reduction of these devices’ performance is obtained due to the presence of ZnS secondary phase and a different back-contact interface formation. This work presents the first promising semitransparent CZGSSe solar cells, opening new paths of applications.This work was supported by CELL2WIN (PID2019-104372RB-C32), InnoPV(PID2022-140226OB-C33) funded by MCIN/AEI/ 10.13039/501100011033and by“ERDF A way of making Europe,”ASSESS (TED2021-129666B-C21and TED2021-129666B-C22) funded by MCIN/AEI/10.13039/501100011033 by the“European Union NextGenerationEU/PRTR”andthe European Project INFINITE-CELL (H2020-MSCA-RISE-2017-777968).M.P. and M.G. acknowledge thefinancial support from the SpanishMinistry of Science, Innovation and Universities within the Ramón yCajal (grant no. RYC-2017-23758) and Ramón y Cajal (grant no.RYC2022-035588-I) programs, respectively. A.R.P. also acknowledgesthefinancial support from Community of Madrid within YouthEmployment Program (grant no. PEJD-2017-PRE/IND-4062).Peer reviewe