simple jump-script (2D)

I just started to make my first game with Unity - a simple Jump 'n Run. I used Rigidbody2D.AddForce for the jump mechanic. Right now I can jump out of the window, if I hold the UpArrow down. What I am looking for is an option to maximize the jump height. I tried to build a trigger-box and putting the jumping-script into an OnTriggerStay-function, but this doesn't work. As I can't find an answer in the Manual, Scripting API or the internet I would appreciate some help :)

That's my current code:

 public class Player : MonoBehaviour 
 {
     public float moveSpeed;
     public float jumpPower;
 
     void Update () 
     {
         if (Input.GetKey(KeyCode.RightArrow))
             transform.Translate(Vector3.right * moveSpeed * Time.deltaTime);
         if (Input.GetKey(KeyCode.LeftArrow))
             transform.Translate(-Vector2.right * moveSpeed * Time.deltaTime);
 
         Rigidbody2D rb = GetComponent<Rigidbody2D> ();
         if (Input.GetKey(KeyCode.UpArrow))
             rb.AddForce(Vector2.up * jumpPower);
     }
 }

What I found in the Scripting API was AddForce.impulse. This sounds like what I am looking for. But unfortunately I am not able to implement it.