We precisely investigate sodium (Na)-induced potential-induced degradation (PID) in n-type front-emitter (n-FE) crystalline silicon (c-Si) photovoltaic (PV) modules, in which open-circuit voltage (Voc) and fill factor deteriorate. Secondary ion mass spectrometry shows Na introduction into n-FE cells by a negative-bias PID stress and a reduction in Na density by positive-bias application. Scanning electron microscopy and energy dispersive X-ray analysis reveal the formation of Na-based protrusions on the cell surface. Silicon nitride (SiNx) disappears at the position of protrusions, which is the root cause for the serious and unrecoverable PID of n-FE c-Si PV modules.
We investigated the effect of silicon dioxide (SiO 2 ) film in n-type front-emitter (n-FE) crystalline Si solar cells on the potential-induced degradation (PID) of n-FE photovoltaic modules. After PID tests by applying a bias of −1000 V at 85 °C for a few min, the modules with the cells without SiO 2 did not degrade in the short-circuit current density and the open-circuit voltage (V oc ). Since the degradation is known to be due to positive charge accumulation in SiN x films, the result suggests that such SiO 2 acts as barriers to retain accumulated positive charges. After further PID tests, modules without SiO 2 show faster and more significant degradation by a decreases in the fill factor (FF) and the V oc . It has been proposed that the degradation in the FF and V oc is caused by sodium (Na) introduction into cells. The results therefore suggest that SiO 2 delays Na migration.
We investigate the effect of silicon nitride (SiNx) films in n-type front-emitter (n-FE) crystalline Si (c-Si) solar cells on the potential-induced degradation (PID) of n-FE photovoltaic (PV) modules. A negative-bias PID test for a few min does not degrade the performance of PV modules with n-FE cells without SiNx/Si dioxide (SiO2) stacks, unlike in the case of PV modules with cells with SiNx/SiO2. This is because of the absence of polarization-type PID. After a longer PID test, the PV modules with n-FE cells without SiNx/SiO2 show a slower decrease in fill factor (FF), originating from Na introduction into the depletion layer of a p–n junction, than the modules with cells with SiNx/SiO2. The mitigation of PID by eliminating SiNx is partly consistent with the results of PV modules with p-type conventional cells without SiNx in which no PID occurs. SiNx thus has a function of enhancing Na introduction into c-Si.
Changes in wettability of carbon nanowalls (CNWs) by oxygen plasma treatment were investigated. Detailed analysis suggests that the changes in wettability of CNW from hydrophobicity to hydrophilicity by oxygen plasma treatment were mainly caused by the formation of hydrophilic nature on the CNW surface. An evaluation technique of penetration of an aqueous solution into CNW structure was also introduced in this paper. By using this technique, it was revealed that the aqueous solution penetrated into the gaps between walls for CNW samples treated by oxygen plasma.
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