Reduced Recombination and Improved Performance of CdSe/CdTe Solar Cells due to Cu Migration Induced by Light Soaking

Abstract

The performance of CdTe solar cells has advanced impressively in recent years with the incorporation of Se. Instabilities associated with light soaking and copper reorganization have been extensively examined for the previous generation of CdS/CdTe solar cells, but instabilities in Cu-doped Se-alloyed CdTe devices remain relatively unexplored. In this work, we fabricated a range of CdSe/CdTe solar cells by sputtering CdSe layers with thicknesses of 100, 120, 150, 180, and 200 nm on transparent oxide-coated glass and then depositing CdTe by close-spaced sublimation. After CdCl2 annealing, Cu-doping, and back metal deposition, a variety of analyses were performed both before and after light soaking to understand the changes in device performance. The device efficiency was degraded with light soaking in most cases, but devices fabricated with a CdSe layer thickness of 120 nm showed reasonably good efficiency initially (13.5%) and a dramatic improvement with light soaking (16.5%). The efficiency improvement is examined within the context of Cu ion reorganization that is well known for CdS/CdTe devices. Low-temperature photoluminescence data and V oc versus temperature measurements indicate a reduction in nonradiative recombination due to the passivation of defects and defect complexes in the graded CdSe x Te1–x layer.

Bifacial CdTe Solar Cells with Copper Chromium Oxide Back‐Buffer Layer

“…The increase in V OC was interpreted as a consequence of the change in the concentration of active defects due to the Cu migration. [36] The carrier density of the CdTe device with Cu x Cr y O z back contact estimated from the C-V analysis is %3.2 Â 10 13 cm À3 , which is lower by a factor of %1.7 compared to the reference device (%5.6 Â 10 13 cm À3 ) with our standard Cu doping through CuCl 2 treatment (Figure 1b). However, it should be noted that the carrier profile estimated from C-V data is prone to the influence of deep levels, back diode, and nonuniform distribution of dopants, which may lead to an apparent change from actual values.…”

“…The increase in V OC was interpreted as a consequence of the change in the concentration of active defects due to the Cu migration. [ 36 ]…”

Oxygen Management to Avoid Photo-Inactive Cd(S,Se) for Efficient Cd(Se,Te) Solar Cells

“…Steady-state photoluminescence (PL) measurements were made with 633 nm laser excitation through the glass to investigate the carrier transport properties for devices 2 and 3, corresponding to the devices without and with proper oxygen management (Table ). As shown in Figure a, the emissions of both devices are dominated by a peak at 873 nm (1.42 eV), which can be assigned to the band-to-band emission of Cd­(Se,Te) . Additionally, two shoulder peaks can be observed at 805 nm (1.54 eV) and 954 nm (1.30 eV), respectively.…”

“…As shown in Figure 2a, the emissions of both devices are dominated by a peak at 873 nm (1.42 eV), which can be assigned to the band-to-band emission of Cd(Se,Te). 21 Additionally, two shoulder peaks can be observed at 805 nm (1.54 eV) and 954 nm (1.30 eV), respectively. The 805 nm photoluminescence is the emission from fluorine-doped SnO 2 transparent conductor on the glass substrate.…”

Operando Characterizations of Light-Induced Junction Evolution in Perovskite Solar Cells

“…Light-soaking effects or light-induced cell performance changes have been observed and studied in inorganic photovoltaic semiconductors such as amorphous silicon and CdTe. For instance, in the most pronounced instance of amorphous silicon solar cells, light soaking causes the well-known Staebler–Wronski effect, resulting in the reduction of photoconductance and an increase of non-radiative recombination due to an increase in dangling bonds caused by a light-induced breaking of silicon–hydrogen bonds. − In CdTe solar cells, copper ion migration from the back copper contact was found to be the main cause of photodegradation. , However, in PSCs, light soaking could cause substantial changes of the intrinsic material as well as when incorporated into the device in a variety of ways, and their origins are still debated. The proposed mechanisms are ion migration that reduces defect densities, , local polarization, , change of photoconductance , or light soaking enhanced electric field and charge accumulation when charge transport occurs between the perovskite semiconductor and the electrode interface, and finally reduced non-radiative recombination that can be induced within the perovskite bulk and at their surfaces and interfaces. , Yet, little is known about the changes in the microscopic properties of perovskite heterojunctions and the evolution of these properties has rarely been characterized during device operation.…”