Photovoltaic devices with InP nanolayers

A.Koval, L.Gorceac, V.Botnariuc, S.Vatavu, P.Ketrush, B.Cinic, S.Raevski, C.Rotaru

Moldova State University, Department of Physics and Engineering, MD-2009 Chisinau, Moldova  E-mail: andrcoval@mail.ru

Indium phosphide (InP) remains as one of promising materials for photovoltaic devices fabrication due to the optimal values of the band gap (1,34 eV) and high optical absorption coefficient (5104 cm-1) at the direct optical transitions and also to the possibility of its combination with other compounds.
This study, being a continuation of the research presented in [1, 2] has the objective to fabricate  photodetectors (PD) and photovoltaic cells (PVC) based on In-n+CdS-po-p+InP-(Ag+5%Zn)  heterojunctions and In-n+CdS-n+po-p+InP-(Ag+ 5%Zn)  homojunctions bu using gaseous phase epitaxy in the In-PCl3-H2 system (for po and n+InP epitaxial layers), the technology of the quasiclosed volume in a H2 ambience (frontal layer n+CdS) and thermal evaporation in vacuum (In, Ag + 5% Zn alloy). The SiO2/ZnO antireflective layers (d=80...110 nm) were deposited by electron beam evaporation (300 K)/pyrolysis spray. InP:Zn single crystal platelets (p=(1…3)1018 cm-3, p=(50…60) cm2V-1s-1) having 100/3 crystallographic direction were used as substrates. The poInP:Zn, nInP:Te and nCdS:In epitaxial layers depending on the technological regime of fabrication, have the charge carriers concentration of (5…50)1016, (0,9…2)1016 and 1018…1019 cm-3  and mobility of (32…97), (1270…1900), (60…100) cm2V-1s-1 (300 K) respectively.
Testing of the hetero- and homojunctions prepared as photodetectors and photovoltaic cells, under standard conditions (AM1), showed that PVC based on HJ of n+CdS-po-p+InP type with SiO2 antireflective coating has the maximum efficiency of 12% for incident light flux of 100 mWcm-2. For PVC, based on homo-junction of n+CdS-n+-po-p+InP type the conversion efficiency reaches a lower value  of 7,31% which is related to the higher series resistance (17,47 Ohmcm2) and, respectively lower fill factor value 72,47%. The heterojunction has the maximum external quantum efficiency of 75… 80% whereas  the  homojunction of 70%.
For HJ of n+CdS-po-p+InP type with SiO2 antireflective layer the photosensitivity covers the wavelength region of  550… 950 nm with the absolute maximum value of 450…500 A/mW for =850 nm. Such heterojunctions can be used as photodetectors in the wavelength region of spectrum (500… 950 nm).

1. A.Koval, L.Gorceac, V.Botnariuc, S.Vatavu, P.Ketrush, B.Cinic, S.Raevski.// Investigation of 
       InP photovoltaic cells with nanolayers. The International Conference «Nanotechnology and 
       nanomaterials» (NANO-2019), Lviv, Ukraine, 2019, -P.435-436.   
2. A.Coval, L.Gorceac, V.Botnariuc, P.Ketrush, B.Cinic, S.Raevski, L.Gagara, C.Rotaru.// InP 
       photovoltaic cells with optimized nanometric layers. The International Conference 
       «Nanotechnology and nanomaterials» (NANO-2018), Kiev, Ukraine, 2018, -P.111-112.