Improved Carrier Collection Research Articles

Photoelectrodes with Enhanced Carrier Generation and Collection Through Optical Simulation and Materials Engineering

AbstractThe efficiency of solar‐fuel conversion in photoelectrochemical (PEC) systems is hindered by significant losses of photons and photocarriers within the photoelectrodes. This study introduces an innovative ITO@In2S3 core‐shell nanowire structure designed to overcome these challenges through cutting‐edge materials engineering and sophisticated simulation techniques. Optical modeling and finite element simulations highlight the conflict between photocarrier generation and collection in planar In2S3 thin films and demonstrate how the core‐shell nanowire geometry can significantly enhance light absorption. The developed ITO@In2S3 nanowire photoanodes achieve a photocurrent of 11.3 mA cm−2 at 1.23 V versus RHE, which is nearly five times greater than that of planar ITO/In2S3 thin films. Characterization techniques, including UV–vis absorption and charge separation efficiency measurements, confirm the enhanced light absorption and improved carrier collection facilitated by broadening the optical absorption range and reducing carrier transport distances. This research not only deepens the understanding of the dynamics within thin‐film photoelectrodes but also paves the way for the development of more efficient technologies for solar fuel conversion.

Improved carrier collection efficiency in CZTS solar cells by Li‐enhanced liquid‐phase‐assisted grain growth

AbstractThe liquid‐phase‐assisted grain growth (LGG) process is a promising strategy to fabricate large‐grain pure sulfide Cu2ZnSnS4 (CZTS) layers that span the absorber thickness and improve the carrier collection efficiency in photovoltaic devices. Li doping is an effective route to promote such LGG process of Cu2ZnSn(S,Se)4 (CZTSSe) as it can provide liquid Li‐Se phase facilitating the growth of large‐grain CZTSSe. However, the detailed function of the added Li in grain growth has rarely been investigated in both CZTS and CZTSSe, as the reported in situ, and pre‐deposition doping strategies usually suffer from substantial Li losses during the spin‐coating process and/or the high‐temperature sulfurization process. Herein, by monitoring the temperature‐dependent Li loss during the sulfurization process, we demonstrate that a small proportion of the added Li can remain at the CZTS film from the early sulfurization stage and provide Li‐S flux to promote the LGG process. An encouraging efficiency of 10.53%, with a remarkably high short‐circuit current density of 22.6 mA/cm2 and open‐circuit voltage of 0.744 V, is achieved by a significantly enlarged grain size of 3 μm with Li addition. This work could enhance the knowledge of employing Li‐S as flux for growing large‐grain chalcogenide absorbers for high performance devices with better carrier transport.

The Fabrication and Characterization of Silicon Surface Grooving Using the CV Etching Technique for Front Deep Metallic Contact Solar Cells

This study experimentally investigated the use of the chemical vapor etching method for silicon surface grooving for regular front deep metallic contact solar cell applications. The thickness of silicon wafers is a crucial parameter in the production of solar cells with front and back buried contacts, because silicon surface grooves result in a larger contact area, which in turn improves carrier collection and increases the collection probability for minority carriers. A simple, low-cost HNO3/HF chemical vapor etching technique was used to create grooves on silicon wafers with the help of a highly effective anti-acid mask. The thick porous layer of powder that was produced was easily dissolved in water, leaving patterned grooved areas on the silicon substrate. A linear dependence was observed between the etched thickness and time, suggesting that the etching process followed a constant etch rate, something that is crucial for ensuring precise and reproducible etching results for the semiconductor and microfabrication industries. Moreover, by creating shorter pathways for charge carriers to travel to their respective contacts, front deep contacts minimize the overall distance they need to traverse and therefore reduce the chance of carrier recombination within the silicon material. As a result, the internal quantum efficiency of solar cells with front deep metallic contacts improved by 35% compared to mc-Si solar cells having planar contacts. The use of front deep contacts therefore represents a forward-looking strategy for improving the performance of silicon solar cells. Indeed, this innovative electrode configuration improves charge carrier collection, mitigates recombination losses, and ultimately leads to more efficient and effective solar energy conversion, which contributes to sustainable energy development in the areas of clean energy resources. Further work needs to be undertaken to develop energy sustainably and consider other clean energy resources.

An ITO-Free Kesterite Solar Cell.

Photovoltaic thin film solar cells based on kesterite Cu2 ZnSn(S, Se)4 (CZTSSe) have reached 13.8% sunlight-to-electricity conversion efficiency. However, this efficiency is still far from the Shockley-Queisser radiative limit and is hindered by the significant deficit in open circuit voltage (VOC ). The presence of high-density interface states between the absorber layer and buffer or window layer leads to the recombination of photogenerated carriers, thereby reducing effective carrier collection. To tackle this issue, a new window structure ZnO/AgNW/ZnO/AgNW (ZAZA) comprising layers of ZnO and silver nanowires (AgNWs) is proposed. This structure offers a simple and low-damage processing method, resulting in improved optoelectronic properties and junction quality. The ZAZA-based devices exhibit enhanced VOC due to the higher built-in voltage (Vbi ) and reduced interface recombination compared to the usual indium tin oxide (ITO) based structures. Additionally, improved carrier collection is demonstrated as a result of the shortened collection paths and the more uniform carrier lifetime distribution. These advances enable the fabrication of the first ITO-free CZTSSe solar cells with over 10% efficiency without an anti-reflectivecoating.

Improved PCE in stable lead-free perovskite solar cells based on band engineering of ETL and absorber

In this paper, a unique structure of graded band gap (GBG) electron transport layer (ETL) based lead-free Perovskite solar cell (PSC) is proposed and numerically investigated. The structure consists of cesium Formamidinium tin iodide (FACsSnI3) with band-gap grading aspect sandwiched between electron and hole transport layers. Various ETLs such as Zn(S,O), ZnO, ZnMgO and C60 have been considered and investigated with and without GBG aspect. It is revealed that the use of band engineering based on band gap grading ETL and absorber films allows the dual-advantages of enhanced photogeneration and carrier extraction mechanisms. The merits of the proposed PSC structure are compared to other published results in terms of improved photovoltaic parameters. The obtained results show improvements in photoconversion properties of the PSCs when GBG-Zn(S,O) is considered as an ETL. The effective conduction band alignment of GBG-Zn(S,O)/GBG-FACsSnI3 heterostructure interface leads to an improved carrier collection efficiency and subsequently improved efficiency. The optimized PSC structure presents power conversion efficiency as high as 21.67 %, with an open circuit voltage of 0.96 V, short-circuit current of 30.75 mA/cm2, and fill factor of 72.88%. The obtained photovoltaic parameters of the proposed GBG-ETL/GBG-FACsSnI3 heterostructure can provide new perspectives for the realization of efficient cost-effective lead-free PSCs.

Perovskite Solar Cells Consisting of PTAA Modified with Monomolecular Layer and Application to All‐Perovskite Tandem Solar Cells with Efficiency over 25%

AbstractThis study is on the enhancement of the efficiency of wide bandgap (FA0.8Cs0.2PbI1.8Br1.2) perovskite solar cells (PSCs) used as the top layer of the perovskite/perovskite tandem solar cell. Poly[bis(4‐phenyl) (2,4,6‐trimethylphenyl) amine] (PTAA) and the monomolecular layer called SAM layer are effective hole collection layers for APbI3 PSCs. However, these hole transport layers (HTL) do not give high efficiencies for the wide bandgap FA0.8Cs0.2PbI1.8Br1.2 PSCs. It is found that the surface‐modified PTAA by monomolecular layer (MNL) improves the efficiency of PSCs. The improved efficiency is explained by the improved FA0.8Cs0.2PbI1.8Br1.2 film quality, decreased film distortion (low lattice disordering) and low density of the charge recombination site, and improves carrier collection by the surface modified PTAA layer. In addition, the relationship between the length of the alkyl group linking the anchor group and the carbazole group is also discussed. Finally, the wide bandgap lead PSCs (Eg = 1.77 eV) fabricated on the PTAA/monomolecular bilayer give a higher power conversion efficiency of 16.57%. Meanwhile, all‐perovskite tandem solar cells with over 25% efficiency are reported by using the PTAA/monomolecular substrate.

Photovoltaic performances of TiO2/Se heterojunction devices with different crystallographic structures of sputter-deposited TiO2 thin films

This study investigates the impact of sputter-deposited TiO2 n-type window layers with varied crystallographic structures on the power conversion of TiO2/Se photovoltaic devices, one of the most promising indoor photovoltaic energy harvesters and wide-gap top cells in tandem solar cells. Since incident light illuminates from TiO2 n-type window layer of TiO2/Se photovoltaic devices, most of photons carriers is absorbed in the Se layer. It is essential for highly efficient photovoltaic conversion of TiO2/Se devices to improve carrier collection by adequate formation of built-in potential in the Se layer and to reduce recombination by optimizing energy band alignment at TiO2/Se interface. In this study, TiO2 window layers with different contents of anatase and rutile crystallographic structures are applied to TiO2/Se heterojunction devices. Impacts of TiO2 n-type window layers with varied crystallographic structures on the power conversion of TiO2/Se photovoltaic devices are investigated in conjunction with different photoconductivity and energy band structures between anatase and rutile TiO2 thin films. In TiO2/Se photovoltaic devices with anatase/rutile mixture window layer, the power conversion efficiency was increased from 3.04% to 4.48% by combining the high open circuit voltage and high short circuit current, owing to the smaller cliff-type conduction band offset at −0.63 eV and smaller series resistance resulting from fitting the current density–voltage curves.

Strategies for reducing the overpotential of one-dimensional Si nanostructured photoelectrodes for solar hydrogen production

Strategies to reduce the overpotential of 1D silicon nanostructured photoelectrodes for solar hydrogen generation: co-catalysts to improve the reaction kinetics, hetero- and homo-junctions to improve carrier collection and enhance photovoltage.

Electricity Generation from Atmospheric Moisture Using a CdS/p‐Si Nanowire Hetero‐Junction Device

AbstractOne‐dimensional heterojunction devices are gaining attention because of improved carrier collection which results in improving the overall efficiency of a device. Herein, we report the synthesis of a CdS/p‐Si nanowire (NW) hetero‐junction device by wet‐chemical methods and their potential application for electricity generation from atmospheric moisture. A single CdS/p‐Si NWs hetero‐junction based moisture enabled electricity generator (MEG) device exhibits a saturated maximum output voltage in the range of 250–300 mV and a saturation current of ∼0.2 μA in presence of humid conditions. This primitive module acts as a promising candidate for future energy generation devices constituting of individual units connected either through simple series or parallel connection to scale up high electrical power.

Enhanced carrier collection efficiency of GeSn single quantum well towards all-group-IV photonics applications

GeSn-based quantum wells (QWs) are of great interests for the development of all-group-IV optoelectronic devices such as lasers. Using a GeSn buffer and SiGeSn barrier has been studied with the aim of obtaining a direct bandgap well and increasing the carrier confinement. However, the carrier collection efficiency with such a configuration remains unsatisfactory. In this work, a single QW with additional GeSn barrier inserted between the GeSn well and the SiGeSn barrier was grown and characterized. Under relatively low carrier injection, the photoluminescence results show dramatically enhanced emission from the QW compared to the reference samples with only SiGeSn barrier, indicating a significantly improved carrier collection efficiency of the well.

Epitaxial Topological Insulator Bi2Te3 for Fast Visible to Mid-Infrared Heterojunction Photodetector by Graphene As Charge Collection Medium.

Three dimensional topological insulators have a thriving application prospect in broadband photodetectors due to the possessed topological quantum states. Herein, a large area and uniform topological insulator bismuth telluride (Bi2Te3) layer with high crystalline quality is directly epitaxial grown on GaAs(111)B wafer using a molecular beam epitaxy process, ensuring efficient out-of-plane carriers transportation due to reduced interface defects influence. By tiling monolayer graphene (Gr) on the as-prepared Bi2Te3 layer, a Gr/Bi2Te3/GaAs heterojunction array prototype was further fabricated, and our photodetector array exhibited the capability of sensing ultrabroad photodetection wavebands from visible (405 nm) to mid-infrared (4.5 μm) with a high specific detectivity (D*) up to 1012 Jones and a fast response speed at about microseconds at room temperature. The enhanced device performance can be attributed to enhanced light-matter interaction at the high-quality heterointerface of Bi2Te3/GaAs and improved carrier collection efficiency through graphene as a charge collection medium, indicating an application prospect of topological insulator Bi2Te3 for fast-speed broadband photodetection up to a mid-infrared waveband. This work demonstrated the potential of integrated topological quantum materials with a conventional functional substrate to fabricate the next generation of broadband photodetection devices for uncooled focal plane array or infrared communication systems in future.

Investigation of SiGeSn/GeSn/SiGeSn single quantum well with enhanced well emission

In this work, a SiGeSn/GeSn/SiGeSn single quantum well was grown and characterized. The sample has a thicker GeSn well of 22nm compared to a previously reported 9nm well configuration. The thicker well leads to: (i) lowered ground energy level in Γ valley offering more bandgap directness; (ii) increased carrier density in the well; and (iii) improved carrier collection due to increased barrier height. As a result, significantly enhanced emission from the quantum well was observed. The strong photoluminescence (PL) signal allows for the estimation of quantum efficiency (QE), which was unattainable in previous studies. Using pumping-power-dependent PL spectra at 20K, the peak spontaneous QE and external QE were measured as 37.9% and 1.45%, respectively.

High-efficiency (>20%) planar carbon-based perovskite solar cells through device configuration engineering

Carbon-based perovskite solar cells (C-PSCs) have attracted widespread research interest because of their excellent stability. However, the power conversion efficiency (PCE) of C-PSCs, especially planar C-PSCs, lags far behind the certified efficiency (25.5%) of metal-based PSCs. The simple architecture of planar C-PSCs imparts stringent requirements for device configuration. In this study, we fabricated high-performance planar C-PSCs through device configuration engineering in terms of the perovskite active layer and carbon electrode. Through the combination of component and additive engineering, the crystallization and absorption profiles of perovskite active layer have been improved, which afforded sufficient photogenerated carriers and decreased nonradiative recombination. Furthermore, the mechanical and physical properties of carbon electrode were evaluated comprehensively to regulate the back-interface contact. Based on the compromise of the flexibility and conductivity of carbon film, an excellent back-interface contact has been formed, which promoted fast interface charge transfer, thereby decreasing interface recombination and improving carrier collection efficiency. Finally, the as-prepared devices achieved a remarkable PCE of up to 20.04%, which is a record-high value for planar C-PSCs. Furthermore, the as-prepared devices exhibited excellent long-term stability. After storage for 1000 h at room temperature and 25% relative humidity without encapsulation, the as-prepared device retained 94% of its initial performance.

Decorrelation of internal quantum efficiency and lasing threshold in AlGaN-based separate confinement heterostructures for UV emission

In this paper, we study the internal quantum efficiency and lasing threshold of AlGaN/GaN separate confinement heterostructures designed for ultraviolet laser emission. We discuss the effect of carrier localization and carrier diffusion on the optical performance. The implementation of graded index separate confinement heterostructures results in an improved carrier collection at the multi-quantum well, which facilitates population inversion and reduces the lasing threshold. However, this improvement is not correlated with the internal quantum efficiency of the spontaneous emission. We show that carrier localization at alloy inhomogeneities results in an enhancement of the radiative efficiency but does not reduce the laser threshold, which is more sensitive to the carrier injection efficiency.

CZTS nanoparticles as an effective hole-transport layer for Sb2Se3 thin-film solar cells

Sb2Se3 is an emerging and promising thin-film photovoltaic absorber material. However, for commonly CdS/Sb2Se3 heterojunction device structure, low carrier concentration and back contact barrier will prevent the further improvement of device efficiency. Here we have successfully applied Cu2ZnSnS4 (CZTS) nanoparticles (NPs) as a hole-transport layer (HTL) to construct a low-cost n-i-p Sb2Se3 solar cell with FTO/CdS/Sb2Se3/CZTS/Carbon configuration. We found that CZTS HTL can effectively suppress the back interface carrier recombination and improve carrier collection efficiency in the Sb2Se3 solar cells. The average Jsc, FF, and efficiency of Sb2Se3 solar cells with an optimum CZTS HTL are increased by 10.64%, 7.91%, and 17.14%, respectively, compared with Sb2Se3 solar cells without a HTL. Consequently, with CZTS NPs as HTL and carbon as electrode, the n-i-p Sb2Se3 solar cells have achieved a champion efficiency of 6.06%.

Sodium doping of solution‐processed amine‐thiol based CIGS solar cells by thermal evaporation of NaCl

AbstractPoor crystallinity, high degree of porosity and rough surfaces are the main drawbacks of solution‐processed CIGS absorbers resulting in lower power conversion efficiencies when compared to vacuum‐based CIGS solar cells. Therefore, promoting absorber grain growth is key to further improve solution‐based solar cell performance. The effect of alkali elements such as Na in CIGS absorbers is generally recognised to have beneficial effects not only on the absorber opto‐electronic properties but also on the grain growth. In this work, thermal evaporation of a thin layer of NaCl prior to selenisation resulted in absorbers with significantly larger CIGS grains than previously seen with Na diffusing directly from the from soda‐lime glass substrate. NaCl is non‐toxic, abundant and readily available compound that has not been typically used as an evaporation source, but rather as an additive into CIGS precursor solution. The effect of Na on these solution‐processed CIGS devices was primarily observed in the spectacular morphological changes leading to improved carrier collection and minority carrier lifetimes, but less on the absorber doping. Transmission electron microscopy (TEM) revealed voids forming around large CIGS grains upon NaCl addition and these had a negative effect on inter‐grain carrier transport. Nonetheless, the resulting device performance doubled from 5% to 10% with addition of Na using this doping approach; however, a compromise between the optimum grain growth and optimum electronic properties had to be made. This study demonstrates a novel, simple and effective Na‐doping strategy for CIGS absorbers and reveals the current limitations of the Na‐doping in solution‐processed atmospherically deposited cells.

Facile Synthesis of Spherical TiO2 Hollow Nanospheres with a Diameter of 150 nm for High-Performance Mesoporous Perovskite Solar Cells

The electron transport layer (ETL) of organic–inorganic perovskite solar cells plays an important role in their power conversion efficiency (PCE). In this study, TiO2 hollow nanospheres with a diameter of 150 nm were prepared by a facile synthesis method. The synthesized TiO2 hollow nanospheres had a highly porous structure with a surface area of 85.23 m2 g−1, which is significantly higher than commercial TiO2 (P25) (54.32 m2 g−1), indicating that they can form an ideal mesoporous layer for Formamidinium iodide-based perovskite solar cells (PSCs). In addition, the nanospheres achieved a remarkable perovskite performance, and the average PCE increased from 12.87% to 14.27% with a short circuit current density of 22.36 mAcm−2, an open voltage of 0.95 V, and a fill factor of 0.65. The scanning electron microscopy images revealed that the enhanced PCE could be due to the improved carrier collection and transport properties of the nanosphere, which enabled efficient filtration of perovskite into the TiO2 mesoporous ETL. The TiO2 hollow nanospheres fabricated in this study show high potential as a high-quality ETL material for efficient (FAPbI3)0.97(MAPbBr3)0.03-based PSCs.

Inverted PTB7-Th:PC71BM organic solar cells with 11.8% PCE via incorporation of gold nanoparticles in ZnO electron transport layer

In bulk hetero-junction organic solar cells (BHJOSCs), light absorption can be improved by employing techniques such as plasmonic effects which can lead to improved device efficiencies. In this manuscript, we demonstrate highly efficient devices obtained upon incorporation of gold nanoparticles (Au NPs) of size 10–20 nm at various concentrations into solution processed ZnO (zinc oxide) electron transport layers (ETLs). The inverted OSC devices of configuration ITO/ZnO:Au NPs/PTB7-Th:PC71BM/MoO3/Ag show the highest power conversion efficiency (PCE) for an optimum concentration of Au NPs (0.05 wt%) in ZnO ETL layer driven by plasmonic effects leading to improved light absorption and improved interface between the active layer and the ETL leading to improved carrier collection. The effects together cause enhancement in the short circuit current density (Jsc) and fill factor (FF) leading to a maximum PCE of 11.8% with an open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF) of 0.80 V, 21.75 mAcm−2, and ~68%, respectively. This PCE is 24% higher than the control device (ZnO ETL without Au NPs) and is among the best observed values for widely explored bulk hetero-junction (BHJ) solar cells based on PTB7-Th:PC71BM.

Eco-Friendly AgBiS2 Nanocrystal / ZnO Nanowire Heterojunction Solar Cells with Enhanced Carrier Collection

Solution-process compatibility and size-dependent bandgap tunability of colloidal quantum dots (CQDs) make them low-cost promising materials for next generation solar cells. Among CQD-based solar cells, heterojunction devices formed with PbS CQDs and ZnO exhibit impressive solar cell performance. However, the hazardous impact of Pb is causing concern. In addition, researches on CQD-based solar cells fabricated using non-toxic and abundant elements are still very limited. Therefore, eco-friendly CQDs for solar cell have drawn much attention. AgBiS2 colloidal nanocrystals with a wide absorption band (0.4-1.2 μm) are one of the alternatives to PbS CQDs. However, the power conversion efficiencies of planar-type heterojunction solar cells using AgBiS2 nanocrystals (NCs) (ITO / ZnO dense layer / AgBiS2 NC layer/ hole transport layers (eg. PTB7:MoOx) / Ag) have been at most approximately 6% mainly due to the short carrier diffusion length of AgBiS2 [2].In this work, thus, we paid our attention to nanowire (NW) structures, with the aim of elongation of carrier diffusion length, and also applied widely-used and less-expensive hole transport materials. We then fabricated NW-type solar cells (ITO / ZnO NW: AgBiS2 mixture / AgBiS2 overlayer / P3HT / Au) by a dip-coating method.We independently tailored ZnO nanowire length and the active device layer thickness to study charge collection in AgBiS2 NW-type solar cell. ZnO NWs were synthesized by a hydrothermal method, and the length of ZnO NW was controlled by the reaction time [3]. As a reference, planar-type solar cells using dense ZnO layers with different thicknesses (NPSC) were also constructed. Jsc values of NPSCs increase as AgBiS2 layer thickness becomes thicker and reach to a maximum value of 12 mA/cm2 at 100 nm. And Jsc then decreases with thickening AgBiS2 layers due to the limited carrier diffusion length of AgBiS2 layer. Whereas in the case of Jsc of NWSCs, the highest Jsc of 20.51 mA / cm2 can be obtained at 200 nm-ZnO NWs. This Jsc value is higher than previously-reported AgBiS2 solar cells (eg. JSC = 15.10 mA/cm2, VOC = 0.46 V, FF = 57%, and PCE = 3.99% [1]), and correspoinding PCE reached 3.97%, approximately doubled the value of planar cell (PCE = 2.06%).Figure 1 shows the EQE spectra obtained with the best performing NWSC and NPSC. It can be seen that NWSC gives high EQE in almost all the spectral region studied. The ZnO NW / AgBiS2 heterojunction enabled achievement of more efficient charge carrier transportation than a planar ZnO NP / AgBiS2 cell. The cell gives a maximum EQE of 80% and shows a wide photocurrent response range of 300-1200 nm. In particular, the EQE is greatly enhanced in the near-infrared region from 35.6% (800 nm) in NPSC to 60.0% in NWSC, indicating improved carrier collection in near-infrared region for NWSC. NWSC also shows higher power conversion efficiency than NPSC because of the higher Jsc of NWSC (inset table in Fig. 1). The length of ZnO NW dependence of NWSC performance was also studied to get a better understanding of diffusion mechanism in NWSC. The structure of NWSCs was optimized by varying nanowire length and active overlayer thickness, carrier transport mechanisms related to the AgBiS2 ZnO-NW blend region and planar AgBiS2 overlayer region were clarified. The solar cell with the 320 nm-thick active layer (200 nm-NW region plus 120 nm-overlayer region) gave the best performance.These results show that ZnO nanowire / AgBiS2 nanocrystal mixtures are useful to achieve more efficient carrier collection. Long-term stability is equally important; at least 3-month air stabilty has been confirmed in NWSCs.[1] M. Bernechea, N. C. Miller, G. Xercavins, et al. Nature Photonics 2016, 10, 521.[2] H. Wang, T. Kubo, J. Nakazaki, T. Kinoshita, H. Segawa. J. Phys. Chem. Lett. 2013, 4, 2455.[3] H. Wang, V. Gonzalez-Pedro, Kubo, T.; F. Fabregat-Santiago, J. Bisquert, Y. Sanehira, J. Nakazaki, H. Segawa. The Journal of Physical Chemistry C 2015, 49, 27265. Figure 1

Tuning the Work Function of the Metal Back Contact toward Efficient Cu2ZnSnSe4 Solar Cells

Carrier collection is crucial for thin film photoelectronic devices. As photoelectronic devices, the undesirable energy band structure between the metal contact and p‐type absorber is a serious limitation to boost the open‐circuit voltage (VOC) of thin film solar cells. Herein, the carrier collection near the back contact of a kesterite solar cell is promoted by tailoring the work function of the back contact. By diffusing P into Mo back contact of the kesterite solar cell, the work function of the Mo back contact is increased from 4.68 to 5.62 eV and the diffused P bonds with Mo as anions, thus resulting in the energy band bending upward at the back interface and enabling the fluent transmission of holes. The efficiency of Cu2ZnSnSe4 solar cells increases from 6.8% to 11.28%. The results expand the path to improving carrier collection in solar cells and electronic devices utilizing metal film contacts.