Interface Engineering For Both Cathode And Anode Enables Highly Efficient Solution-processed CdTe Nanocrystal Solar Cells

The solution-processed Cadmium telluride?CdTe?nanocrystal solar cells have attracted much attention and made great progress due to its simple manufacturing process,high utilization of raw materials,stable performance,low cost,and compatibility with flexible substrates.At present,the highest power conversion efficiency?PCE?of CdTe nanocrystal solar cells has been more than 10%,but there is a certain gap compared with CdTe thin film solar cells?22.1%?.The main factors limiting the device performance are as follow:there is an energetic barrier between CdTe and the contact electrode;the carrier transport between the electron transport layers is suppressed;a low spectrum response is produced in the short wavelength region due to the low carrier lifetime of the n-type layers?such as CdS?.For these,this paper mainly focuses on the interface engineer of the device.By introducing an electron transport layer and a hole transport layer,the efficiency of carrier separation,transmission and collection is improved,which enables highly efficient CdTe nanocrystal solar cells.The content of this paper are as follows:?1?the CdS/CdSe bilayered electron transport layer is introduced,which not only improves the optical collection efficiency,but also reduces the carrier recombination and electron injection barrier at the cathode interface.After optimization,the solution-processed CdTe nanocrystal solar cell with an inverted structure of ITO/Zn O/CdS/CdSe/CdTe/Au shows an open-circuit voltage of 0.65 V,a short-circuit current density of 23.18 m A cm^-2,and a fill factor of 52.37%,resulting in a PCE of 7.82%.For comparison,the devices with single electron transport layer are 5.60%?device structure:ITO/Zn O/CdS/CdTe/Au?and 5.86%?device structure:ITO/Zn O/CdS/CdSe/CdTe/Au?,respectively.Obviously,the devices with CdS/CdSe bilayered electron transport layer have a higher PCE.It is worth noting that these devices show a good repeatability and stability,and there is no obvious performance degradation in long-term storage in the atmosphere.?2?A new crosslinkable polymer poly?phenylphosphine-co-4-vinyl-triphenylamine??P-TPA?with high work function is used as hole transport material.By forming a dipole layer between CdTe and the electrode,P-TPA layer can reduce the hole injection barrier,improve the hole mobility and carrier lifetime of the device,and achieve efficient hole transmission.The as-optimized CdTe nanocrystal solar cell with a P-TPA layer delivers an open-circuit voltage of 0.72 V,a short-circuit current density of 25.31 m A cm^-2,and a fill factor of 50.49%,leading to a high PCE of9.20%.To the best of our knowledge,the PCE achieved is the highest value ever reported for solution-processed CdTe nanocrystal solar cells without a voltage/light soaking process.Moreover,the PCE value is increased by 18%compared to the device without P-TPA interface modification.In general,we have studied a novel strategy of interface engineering for both cathode and anode to enable highly efficient solution-processed CdTe nanocrystal solar cells,which provides a new route for improving solution-processed CdTe nanocrystal device performance.